{"collection":"philosophy-ethics","full_text_available":true,"graph_url":"https://unchartedknowledge.5gfusion.net/v2/api/page/gutenberg_44388/graph","html_url":"https://unchartedknowledge.5gfusion.net/v2/page/gutenberg_44388","id":"gutenberg_44388","license":"Public Domain (US)","rights_basis":"gutenberg_metadata_copyright_false","source":"gutenberg","source_url":"https://www.gutenberg.org/ebooks/44388","summary":null,"tags":["Biology -- Philosophy","Category: Philosophy & Ethics","Category: Science - Biology","Organism (Philosophy)","Science -- Philosophy"],"text":"Transcriber\u2019s notes:\n\nIn this transcription, italic text is denoted by *asterisks* and bold\ntext by =equal signs=. Subscripts are indicated by _underscores_ (e.g.\n*a*_1 and *b*_1 in Fig.5 caption) and superscripts by ^ (e.g. *a*^1. in\nFig. 9 caption).\n\nPage footnotes (renumbered in consecutive order) are now located\nimmediately below the relevant paragraphs.\n\nThe rare spelling typos noted in the original text have been corrected\nsilently (e.g. invividual-->individual, hyberbola-->hyperbola) but\ninconsistent use of the ligature \u00e6/ae (e.g. pal\u00e6ontology/palaeontology),\ninconsistent use of alternative spellings (e.g. learned/learnt), and\noccasional inconsistencies of hyphenation have been left as in the\noriginal. Minor punctuation typos have been corrected silently (e.g.\nindex entries with missing commas). The abbreviation viz. appears in\nboth roman and italic font.\n\nFormatting of entries in the Table of Contents does not accurately\nmatch that of the corresponding headings in the text, particularly the\nheading Pt.I-B-3 which contains an extraneous \u03b1.\n\nIn Figure 12 caption, multiple ditto marks have been replaced by the\nrelevant text for greater clarity.\n\n\n\n\n\n                       THE SCIENCE AND PHILOSOPHY\n                            OF THE ORGANISM\n\n\n\n\n          AGENTS\n\n            America        The Macmillan Company\n                             64 & 66 Fifth Avenue, New York\n\n            Australasia    The Oxford University Press, Melbourne\n\n            Canada         The Macmillan Company of Canada, Ltd.\n                             27 Richmond Street West, Toronto\n\n            India          Macmillan & Company, Ltd.\n                             Macmillan Building, Bombay\n                             309 Bow Bazaar Street, Calcutta\n\n\n\n\n                                  THE\n                         SCIENCE AND PHILOSOPHY\n                            OF THE ORGANISM\n\n                 THE GIFFORD LECTURES DELIVERED BEFORE\n                       THE UNIVERSITY OF ABERDEEN\n                            IN THE YEAR 1907\n\n                                   BY\n                          HANS DRIESCH, Ph.D.\n                               HEIDELBERG\n\n\n                                 LONDON\n                         ADAM AND CHARLES BLACK\n                                  1908\n\n                         *All rights reserved*\n\n\n\n\nPREFACE\n\n\nThis work is not a text-book of theoretical biology; it is a systematic\npresentment of those biological topics which bear upon the true\nphilosophy of nature. The book is written in a decidedly subjective\nmanner, and it seems to me that this is just what \u201cGifford Lectures\u201d\nought to be. They ought never to lose, or even try to lose, their\ndecidedly personal character.\n\nMy appointment as Gifford Lecturer, the news of which reached me in\nFebruary 1906, came just at the right moment in the progress of my\ntheoretical studies. I had always tried to improve my previous books by\nadding notes or altering the arrangement; I also had left a good deal of\nthings unpublished, and thus I often hoped that I might have occasion\nto arrange for a new, improved, and enlarged edition of those books.\nThis work then is the realisation of my hopes; it is, in its way, a\ndefinitive statement of all that I have to say about the Organic.\n\nThe first volume of this work, containing the lectures for 1907--though\nthe division into \u201clectures\u201d has not been preserved--consists of Parts\nI. and II. of Section A, \u201cThe Chief Results of Analytical Biology.\u201d\nIt gives in Part I. a shortened, revised, and, as I hope, improved\naccount of what was published in my *Analytische Theorie der organischen\nEntwickelung* (1894), *Die Localisation morphogenetischer Vorg\u00e4nge;\nein Beweis Vitalistischen Geschehens* (1899), and *Die organischen\nRegulationen* (1901), though for the professed biologist the two\nlast-named books are by no means superseded by the new work. Part II.\nhas never been published in any systematic form before, though there are\nmany remarks on Systematics, Darwinism, etc., in my previous papers.\n\nThe second volume--to be published in the autumn, after the delivery of\nthe 1908 lectures--will begin with the third and concluding part of the\nscientific section, which is a very carefully revised and rearranged\nsecond edition of my book, *Die \u201cSeele\u201d als elementarer Naturfactor*\n(1903). The greater part of this volume, however, will be devoted to the\n\u201cPhilosophy of the Organism,\u201d *i.e.* Section B, which, in my opinion,\nincludes the most important parts of the work.\n\nSome apology is needed for my presuming to write in English. I was\nled to do so by the conviction, mistaken perhaps, that the process of\ntranslation would rob the lectures of that individual and personal\ncharacter which, as I said before, seems to me so much to be desired. I\nwished nothing to come between me and my audience. I accordingly wrote\nmy manuscript in English, and then submitted it to linguistic revision\nby such skilled aid as I was able to procure at Heidelberg. My reviser\ntells me that if the result of his labours leaves much to be desired,\nit is not to be wondered at, but that, being neither a biologist nor a\nphilosopher, he has done his best to make me presentable to the English\nreader. If he has failed in his troublesome task, I know that it is not\nfor want of care and attention, and I desire here to record my sense of\nindebtedness to him. He wishes to remain anonymous, but I am permitted\nto say that, though resident in a foreign university, he is of Scottish\nname and English birth.\n\nMy gratitude to my friends at Aberdeen, in particular to Professor and\nMrs. J. A. Thomson, for their hospitality and great kindness towards me\ncannot be expressed here; they all know that they succeeded in making me\nfeel quite at home with them.\n\nI am very much obliged to my publishers, Messrs. A. and C. Black, for\ntheir readiness to fulfil all my wishes with respect to publication.\n\n\nThe lectures contained in this book were written in English by a\nGerman and delivered at a Scottish university. Almost all of the ideas\ndiscussed in it were first conceived during the author\u2019s long residence\nin Southern Italy. Thus this book may be witness to the truth which,\nI hope, will be universally recognised in the near future--that all\nculture, moral and intellectual and aesthetic, is not limited by the\nbounds of nationality.\n\n  HANS DRIESCH.\n\n  Heidelberg, *2nd January 1908*.\n\n\n\n\nCONTENTS OF THE FIRST VOLUME\n\n\n                             THE PROGRAMME\n\n                                                                   PAGE\n  On Lord Gifford\u2019s Conception of \u201cScience\u201d                           1\n  Natural Sciences and \u201cNatural Theology\u201d                             3\n  Our Philosophical Basis                                             5\n  On Certain Characteristics of Biology as a Science                  9\n  The Three Different Types of Knowledge about Nature                13\n  General Plan of these Lectures                                     15\n  General Character of the Organic Form                              19\n\n\n          SECTION A.--THE CHIEF RESULTS OF ANALYTICAL BIOLOGY\n\n  PART I.--THE INDIVIDUAL ORGANISM WITH REGARD TO FORM AND METABOLISM\n\n  *A.* ELEMENTARY MORPHOGENESIS--\n\n    Evolutio and Epigenesis in the old Sense                         25\n    The Cell                                                         27\n    The Egg: its Maturation and Fertilisation                        31\n    The First Developmental Processes of Echinus                     33\n    Comparative Embryology                                           44\n    The First Steps of Analytical Morphogenesis                      45\n    The Limits of Pure Description in Science                        50\n\n  *B.* EXPERIMENTAL AND THEORETICAL MORPHOGENESIS--\n\n  1. THE FOUNDATIONS OF THE PHYSIOLOGY OF DEVELOPMENT.\n    \u201cEVOLUTIO\u201d AND \u201cEPIGENESIS\u201d                                      52\n\n    The Theory of Weismann                                           52\n    Experimental Morphology                                          56\n    The Work of Wilhelm Roux                                         58\n    The Experiments on the Egg of the Sea-urchin                     59\n    On the Intimate Structure of the Protoplasm of the Germ          65\n    On some Specificities of Organisation in Certain Germs           70\n    General Results of the First Period of \u201cEntwickelungsmechanik\u201d   71\n    Some New Results concerning Restitutions                         74\n\n  2. ANALYTICAL THEORY OF MORPHOGENESIS                              76\n\n    \u03b1. THE DISTRIBUTION OF MORPHOGENIC POTENCIES                     76\n\n      Prospective Value and Prospective Potency                      76\n      The Potencies of the Blastomeres                               79\n      The Potencies of Elementary Organs in General                  80\n      Explicit and Implicit Potencies: Primary and Secondary\n        Potencies                                                    83\n      The Morphogenetic Function of Maturation in the Light of\n        Recent Discoveries                                           85\n      The Intimate Structure of Protoplasm: Further Remarks          88\n      The Neutrality of the Concept of \u201cPotency\u201d                     89\n\n    \u03b2. THE \u201cMEANS\u201d OF MORPHOGENESIS                                  89\n\n    \u03b2\u2032. The Internal Elementary Means of Morphogenesis                90\n\n      Some Remarks on the Importance of Surface Tension in\n        Morphogenesis                                                91\n      On Growth                                                      93\n      On Cell-division                                               94\n\n    \u03b2\u2033. The External Means of Morphogenesis                          95\n\n      The Discoveries of Herbst                                      96\n\n    \u03b3. THE FORMATIVE CAUSES OR STIMULI                               99\n\n      The Definition of Cause                                        99\n      Some Instances of Formative and Directive Stimuli             102\n\n    \u03b4. THE MORPHOGENETIC HARMONIES                                  107\n\n    \u03b5. ON RESTITUTIONS                                              110\n\n      A few Remarks on Secondary Potencies and on Secondary\n        Morphogenetic Regulations in General                        110\n      The Stimuli of Restitutions                                   113\n\n  3. THE PROBLEM OF MORPHOGENETIC LOCALISATION: THE\n     THEORY OF THE HARMONIOUS-EQUIPOTENTIAL SYSTEM--FIRST\n     PROOF OF THE AUTONOMY OF LIFE                                  118\n\n    The General Problem                                             118\n    The Morphogenetic \u201cSystem\u201d                                      119\n    The \u201cHarmonious-equipotential System\u201d                           122\n    Instances of \u201cHarmonious-equipotential Systems\u201d                 126\n    The Problem of the Factor *E*                                   132\n    No Explanation offered by \u201cMeans\u201d or \u201cFormative Stimuli\u201d        132\n    No Explanation offered by a Chemical Theory of Morphogenesis    134\n    No Machine Possible Inside the Harmonious Systems               138\n    The Autonomy of Morphogenesis proved                            142\n    \u201cEntelechy\u201d                                                     143\n    Some General Remarks on Vitalism                                145\n    The Logic of our First Proof of Vitalism                        146\n\n  4. ON CERTAIN OTHER FEATURES OF MORPHOGENESIS ADVOCATING\n     ITS AUTONOMY                                                   150\n\n    Harmonious-equipotential Systems formed by Wandering Cells      151\n    On Certain Combined Types of Morphogenetic Systems              153\n    The \u201cMorphaesthesia\u201d of Noll                                    157\n    Restitutions of the Second Order                                158\n    On the \u201cEquifinality\u201d of Restitutions                           159\n    Remarks on \u201cRetro-Differentiation\u201d                              163\n\n  *C.* ADAPTATION--\n\n  INTRODUCTORY REMARKS ON REGULATIONS IN GENERAL                    165\n\n  1. MORPHOLOGICAL ADAPTATION                                       168\n\n    The Limits of the Concept of Adaptation                         168\n    Adaptations to Functional Changes from Without                  172\n    True Functional Adaptation                                      176\n    Theoretical Conclusions                                         179\n\n  2. PHYSIOLOGICAL ADAPTATION                                       184\n\n    Specific Adaptedness *not* \u201cAdaptation\u201d                         186\n    Primary and Secondary Adaptations in Physiology                 188\n    On Certain Pre-requisites of Adaptations in General             189\n    On Certain Groups of Primary Physiological Adaptations          190\n\n    General Remarks on Irritability                                 190\n    The Regulation of Heat Production                               193\n    Primary Regulations in the Transport of Materials and\n      Certain Phenomena of Osmotic Pressure                         194\n    Chromatic Regulations in Algae                                  197\n    Metabolic Regulations                                           198\n\n    Immunity the only Type of a Secondary Physiological\n      Adaptation                                                    204\n    No General Positive Result from this Chapter                    209\n    A few Remarks on the Limits of Regulability                     212\n\n  *D.* INHERITANCE. SECOND PROOF OF THE AUTONOMY OF LIFE--\n\n    The Material Continuity in Inheritance                          214\n    On Certain Theories which Seek to Compare Inheritance to Memory 216\n    The Complex-Equipotential System and its R\u00f4le in Inheritance    219\n    The Second Proof of Life-Autonomy. Entelechy at the Bottom\n      of Inheritance                                                224\n    The Significance of the Material Continuity in Inheritance      227\n    The Experimental Facts about Inheritance                        228\n    The R\u00f4le of the Nucleus in Inheritance                          233\n    Variation and Mutation                                          237\n\n  *CONCLUSIONS FROM THE FIRST MAIN PART OF THESE LECTURES*          240\n\n\n                   PART II.--SYSTEMATICS AND HISTORY\n\n  *A.* THE PRINCIPLES OF SYSTEMATICS--\n\n    Rational Systematics                                            243\n    Biological Systematics                                          246\n\n  *B.* THE THEORY OF DESCENT--\n\n  1. GENERALITIES                                                   250\n\n    The Covert Presumption of all Theories of Descent               253\n    The Small Value of Pure Phylogeny                               255\n    History and Systematics                                         257\n\n  2. THE PRINCIPLES OF DARWINISM                                    260\n\n    Natural Selection                                               261\n    Fluctuating Variation the Alleged Cause of Organic Diversity    264\n    Darwinism Fails all along the Line                              269\n\n  3. THE PRINCIPLES OF LAMARCKISM                                   271\n\n    Adaptation as the Starting-Point                                272\n    The Active Storing of Contingent Variations as a\n      Hypothetic Principle                                          273\n    Criticism of the \u201cInheritance of Acquired Characters\u201d\n      assumed by Lamarckism                                         275\n    Other Principles Wanted                                         281\n    Criticism of the Hypothesis of Storing and Handing Down\n      Contingent Variations                                         282\n\n  4. THE REAL RESULTS AND THE UNSOLVED PROBLEMS OF TRANSFORMISM     290\n\n  5. THE LOGICAL VALUE OF THE ORGANIC FORM ACCORDING TO THE\n     DIFFERENT TRANSFORMISTIC THEORIES                              293\n\n    The Organic Form and Entelechy                                  294\n\n  *C.* THE LOGIC OF HISTORY                                         297\n\n  1. THE POSSIBLE ASPECTS OF HISTORY                                299\n\n  2. PHYLOGENETIC POSSIBILITIES                                     304\n\n  3. THE HISTORY OF MANKIND                                         306\n\n    Cumulations in Human History                                    308\n    Human History not an \u201cEvolution\u201d                                311\n    The Problem of the \u201cSingle\u201d as such                             315\n\n  *CONCLUSIONS ABOUT SYSTEMATICS AND HISTORY IN GENERAL*            322\n\n\n\n\nTHE PROGRAMME\n\n\nON LORD GIFFORD\u2019S CONCEPTION OF \u201cSCIENCE\u201d\n\nThis is the first time that a biologist has occupied this place; the\nfirst time that a biologist is to try to carry out the intentions of the\nnoble and high-minded man to whom this lectureship owes its foundation.\n\nOn such an occasion it seems to be not undesirable to inquire what Lord\nGifford\u2019s own opinions about natural science may have been, what place\nin the whole scheme of human knowledge he may have attributed to those\nbranches of it which have become almost the centre of men\u2019s intellectual\ninterest.\n\nAnd, indeed, on studying Lord Gifford\u2019s bequest with the object of\nfinding in it some reference to the natural sciences, one easily notes\nthat he has assigned to them a very high place compared with the other\nsciences, at least in one respect: with regard to their methods.\n\nThere is a highly interesting passage in his will which leaves no doubt\nabout our question. After having formally declared the foundation of\nthis lectureship \u201cfor Promoting, Advancing, Teaching and Diffusing\nthe study of Natural Theology in the widest sense of that term,\u201d and\nafter having arranged about the special features of the lectures, he\ncontinues: \u201cI wish the lecturers to treat their subject as a strictly\nnatural science, the greatest of all possible sciences, indeed, in one\nsense, the only science, that of Infinite Being.... I wish it considered\njust as astronomy or chemistry is.\u201d\n\nOf course, it is not possible to understand these words of Lord\nGifford\u2019s will in a quite literal sense. If, provisionally, we call\n\u201cnatural theology\u201d the ultimate conclusions which may be drawn from a\nstudy of nature in connection with all other results of human sciences,\nthere cannot be any doubt that these conclusions will be of a rather\ndifferent character from the results obtained in, say, the special field\nof scientific chemistry. But, nevertheless, there are, I think, two\npoints of contact between the wider and the narrower field of knowledge,\nand both of them relate to method. Lord Gifford\u2019s own phrase, \u201cInfinite\nBeing,\u201d shows us one of these meeting-points. In opposition to history\nof any form, natural sciences aim at discovering such truths as are\nindependent of special time and of special space, such truths as are\n\u201cideas\u201d in the sense of Plato; and such eternal results, indeed, always\nstand in close relation to the ultimate results of human knowledge\nin general. But besides that there is still another feature which\nmay be common both to \u201cnatural theology\u201d and to the special natural\nsciences, and which is most fully developed in the latter: freedom from\nprepossessions. This, at least, is an ideal of all natural sciences;\nI may say it is *the* ideal of them. That it was this feature which\nLord Gifford had in view in his comparison becomes clear when we read\nin his will that the lectures on natural theology are to be delivered\n\u201cwithout reference to or reliance upon any supposed special exceptional\nor so-called miraculous revelation.\u201d\n\nSo we might say that both in their logical and their moral methods,\nnatural sciences are to be the prototype of \u201cNatural Theology\u201d in Lord\nGifford\u2019s sense.\n\n\nNATURAL SCIENCES AND \u201cNATURAL THEOLOGY\u201d\n\nBut now let us study in a more systematic manner the possible relations\nof the natural sciences to natural theology as a science.\n\nHow is it possible for a natural scientist to contribute to the science\nof the highest and ultimate subject of human knowledge?\n\nAlmost all natural sciences have a sort of na\u00efvet\u00e9 in their own spheres;\nthey all stand on the ground of what has been called a na\u00efve realism,\nas long as they are, so to say, at home. That in no way prejudices\ntheir own progress, but it seems to stand in the way of establishing\ncontact with any higher form of human knowledge than themselves.\nOne may be a first-rate organic chemist even when looking upon the\natoms as small billiard balls, and one may make brilliant discoveries\nabout the behaviour of animals even when regarding them in the most\nanthropomorphic manner--granted that one is a good observer; but it\ncan hardly be admitted that our chemist would do much to advance the\ntheory of matter, or our biologist to solve the problem of the relations\nbetween body and mind.\n\nIt is only by the aid of philosophy, or I would rather say by keeping\nin constant touch with it, that natural sciences are able to acquire\nany significance for what might be called *the* science of nature in the\nmost simple form. Unhappily the term \u201cnatural philosophy\u201d is restricted\nin English to theoretical physics. This is not without a high degree of\njustification, for theoretical physics has indeed lost its na\u00efvet\u00e9 and\nbecome a philosophy of nature; but it nevertheless is very unfortunate\nthat this use of the term \u201cnatural philosophy\u201d is established in\nthis country, as we now have no proper general term descriptive of a\nnatural science that is in permanent relation to philosophy, a natural\nscience which does not use a single concept without justifying it\nepistemologically, *i.e.* what in German, for instance, would simply be\ncalled \u201cNaturphilosophie.\u201d\n\nLet us call it philosophy of nature; then we may say that only by\nbecoming a true philosophy of nature are natural sciences of all sorts\nable to contribute to the highest questions which man\u2019s spirit of\ninquiry can suggest.\n\nThese highest questions themselves are the outcome of the combination\nof the highest results of all branches of philosophy, just as our\nphilosophy of nature originated in the discussion of the results of\nall the separate natural sciences. Are those highest questions not\nonly to be asked, are they to be also solved? To be solved in a way\nwhich does not exceed the limits of philosophy as the domain of actual\nunderstanding?\n\nThe beginning of a long series of studies is not the right place to\ndecide this important question; and so, for the present certainly,\n\u201cnatural theology\u201d must remain a problem. In other words: it must\nremain an open question at the beginning of our studies, whether after\nall there can be any final general answer, free from contradictions,\napplicable to the totality of questions asked by all the branches of\nphilosophy.\n\nBut let us not be disturbed by this problematic entrance to our studies.\nLet us follow biology on its own path; let us study its transition from\na \u201cna\u00efve\u201d science to a real branch of the philosophy of nature. In this\nway we perhaps shall be able to understand what its part may be in\nsolving what can be solved.\n\nThat is to be our subject.\n\n\nOUR PHILOSOPHICAL BASIS\n\nWe call *nature* what is given to us in space.\n\nOf course we are not obliged in these lectures to discuss the\npsychological and epistemological problems of space with its three\ndimensions, nor are we obliged to develop a general theory of reality\nand its different aspects. A few epistemological points will be\nconsidered later at proper times, and always in connection with results\nof theoretical biology.\n\nAt present it must suffice to say that our general philosophical point\nof view will be idealistic, in the critical meaning of the word. The\nuniverse, and within the universe nature, in the sense just defined,\nis my phenomenon. That is what I know. I know nothing more, either\npositively or negatively; that is to say, I do not know that the world\nis *only my* phenomenon, but, on the other hand, I know nothing about\nits \u201cabsolute reality.\u201d And more, I am not even able to describe in\nintelligible words what \u201cabsolute reality\u201d might mean. I am fully\nentitled to state: the universe *is* as truly as I am--though in\na somewhat different sense of \u201cbeing\u201d--and I *am* as truly as the\nuniverse is; but I am not entitled to state anything beyond these\ntwo corresponding phrases. You know that, in the history of European\nphilosophy at least, Bishop Berkeley was the first clearly to outline\nthe field of idealism.\n\nBut my phenomenon--the world, especially nature--consists of elements\nof two different kinds: some of them are merely passive, some of them\ncontain a peculiar sort of activity in themselves. The first are\ngenerally called sensations, but perhaps would be better called elements\nor presentations; the others are forms of construction, and, indeed,\nthere is an active element embraced in them in this sense, that they\nallow, by their free combination, the discovery of principles which\nare not to be denied, which must be affirmed, whenever their meaning\nis understood. You know that I am speaking here of what are generally\ncalled categories and synthetic judgments *a priori*, and that it was\nKant who, on the foundations laid by Locke, Hume, and Leibnitz, first\ngave the outlines of what may be called the real system of critical\nphilosophy. Indeed, our method will be to a great extent Kantian, though\nwith certain exceptions; it is to be strictly idealistic, and will not\nin the Kantian way operate with things in themselves; and it regards\nthe so-called \u201csynthetic judgment *a priori*\u201d and the problem of the\nrelation between categorical principles and experience in a somewhat\ndifferent manner. We think it best to define the much disputed concept\n\u201c*a priori*\u201d as \u201cindependent of the *amount* of experience\u201d; that is\nto say, all categories and categorical principles are brought to my\nconsciousness by that fundamental event which is called experience, and\ntherefore are not independent of it, but they are not inferences from\nexperience, as are so-called empirical laws. We almost might say that we\nonly have to be reminded of those principles by experience, and, indeed,\nwe should not, I think, go very far wrong in saying that the Socratic\ndoctrine, that all knowledge is recollection, holds good as far as\ncategories and categorical principles are in question.\n\nBut enough at present about our general philosophy.\n\nAs to the philosophy of nature, there can be no doubt that, on the basis\nof principles like those we have shortly sketched, its ultimate aim must\nbe to co-ordinate everything in nature with terms and principles of the\ncategorical style. The philosophy of nature thus becomes a system; a\nsystem of which the general type is afforded by the innate constructive\npower of the Ego. In this sense the Kantian dictum remains true, that\nthe Ego prescribes its own laws to nature, though, of course, \u201cnature,\u201d\nthat is, what is given in space, must be such as to permit that sort of\n\u201cprescription.\u201d\n\nOne often hears that all sciences, including the science of sciences,\nphilosophy, have to find out what is true. What, then, may be called\n\u201ctrue\u201d by an idealistic philosopher, for whom the old realistic formula\nof the conformity between knowledge and the object cannot have any\nmeaning? Besides its ordinary application to simple facts or to simple\njudgments, where the word truth only means absence of illusion or no\nfalse statement, truth can be claimed for a philosophical doctrine or\nfor a system of such doctrines only in the sense that there are no\ncontradictions amongst the parts of the doctrine or of the system\nthemselves, and that there are no features in them which impel our\ncategorical Ego to further analysis.\n\nThose of you who attended Professor Ward\u2019s lectures on \u201cNaturalism and\nAgnosticism,\u201d or who have read his excellent book on that subject, will\nknow what the aims of a theory of matter are. You will also be aware\nthat, at present, there does not exist any theory of matter which can\nclaim to be \u201ctrue\u201d; there are contradictions in every theory of matter,\nand, moreover, there are always some points where we are obliged to ask\nfor further information and receive no answer. Experience here has not\nyet aroused all the categorical functions which are needed in order to\nform one unity out of what seem to be incompatibilities at the present\nday. Why is that? Maybe because experience is not yet complete in this\nfield, but maybe also because the whole subject is so complicated\nthat it takes much time to attach categorical functions to what is\nexperienced.\n\nBut it is not our object here to deal either with epistemology proper\nor with ontology: a full analysis of biological facts is our problem.\nWhy, then, all these introductions? why all these philosophical sketches\nin fields of knowledge which have quite another relation to philosophy\nthan biology has? Biology, I hear some one say, is simply and solely\nan empirical science; in some sense it is nothing but applied physics\nand chemistry, perhaps applied mechanics. There are no fundamental\nprinciples in biology which could bring it in any close contact with\nphilosophy. Even the one and only principle which might seem to be\nan innate principle of our experience about life, the principle of\nevolution, is only a combination of more simple factors of the physical\nand chemical type.\n\nIt will be my essential endeavour to convince you, in the course of\nthese lectures, that such an aspect of the science of biology is wrong;\nthat biology is an elemental natural science in the true sense of the\nword.\n\nBut if biology is an elemental science, then, and only then, it stands\nin close relations to epistemology and ontology--in the same relations\nto them, indeed, as every natural science does which deals with true\nelements of nature, and which is willing to abandon na\u00efve realism and\ncontribute its share to the whole of human knowledge.\n\nAnd, therefore, a philosophical sketch is not out of place at the\nbeginning of lectures on the Philosophy of the Organism. We may be\nforced, we, indeed, shall be forced, to remain for some time on the\nground of realistic empiricism, for biology has to deal with very\ncomplicated experiences; but there will be a moment in our progress when\nwe shall enter the realm of the elemental ontological concepts, and\nin that very moment our study of life will have become a part of real\nphilosophy. It was not without good reasons, therefore, that I shortly\nsketched, as a sort of introduction to my lectures, the general point of\nview which we shall take with regard to philosophical questions, and to\nquestions of the philosophy of nature in particular.\n\n\nON CERTAIN CHARACTERISTICS OF BIOLOGY AS A SCIENCE\n\nBiology is the science of life. Practically, all of you know what a\nliving being is, and therefore it is not necessary to formulate a\ndefinition of life, which, at the beginning of our studies, would be\neither provisional and incomplete, or else dogmatic. In some respects,\nindeed, a definition should rather be the end of a science than its\nopening.\n\nWe shall study the phenomena of living organisms analytically, by the\naid of experiment; our principal object will be to find out laws in\nthese phenomena; such laws will then be further analysed, and precisely\nat that point we shall leave the realm of natural science proper.\n\nOur science is the highest of all natural sciences, for it embraces as\nits final object the actions of man, at least in so far as actions also\nare phenomena observable on living bodies.\n\nBut biology is also the most difficult of all natural sciences, not\nonly from the complexity of the phenomena, which it studies, but in\nparticular for another reason which is seldom properly emphasised, and\ntherefore will well repay us for a few words devoted to it.\n\nExcept so far as the \u201celements\u201d of chemistry come into account, the\nexperimenter in the inorganic fields of nature is not hampered by the\nspecificity of composite objects: he makes all the combinations he\nwants. He is always able to have at his disposal red rays of a desired\nwave length when and where he wants, or to have, at a given time and\nplace, the precise amount of any organic compound which he wishes to\nexamine. And he forces electricity and electromagnetism to obey his\nwill, at least with regard to space, time, and intensity of their\nappearance.\n\nThe biologist is not able to \u201cmake\u201d life, as the physicist has made red\nrays or electromagnetism, or as the chemist has made a certain compound\nof carbon. The biologist is almost always in that strange plight in\nwhich the physicist would be if he always had to go to volcanoes in\norder to study the conductivity of heat, or if he had to wait for\nthunderstorms in order to study electricity. The biologist is dependent\non the specificity of living objects as they occur in nature.\n\nA few instances may show you what great inconveniences may hence arise\nto impede practical biological research. We later on shall have to deal\nwith experiments on very young embryos: parts of the germ will have\nto be destroyed in order to study what will happen with the rest. Now\nalmost all germs are surrounded by a membrane; this membrane has to be\ndetached before any operation is possible. But what are we to do if it\nis not possible to remove the membrane without killing the embryo? Or\nwhat if, as for instance in many marine animals, the membrane may be\nremoved but the germs are killed by contact with sea-water? In both\ncases no experiments at all will be possible on a sort of germ which\notherwise, for some special circumstances of its organisation, might\nhave given results of importance. These results become impossible for\nonly a practical, for a very secondary reason; but enough: they are\nimpossible, and they might have thrown light on problems which now\nmust remain problems. Quite the same thing may occur in experiments\non physiology proper or functional physiology: one kind of animals\nsurvives the operation, the other kind does not, and therefore, for\nmerely extrinsic reasons, the investigations have to be restricted to\nthe first, though the second might have given more important results.\nAnd thus the biological experimenter always finds himself in a sort of\ndependence on his subjects, which can hardly be called pleasant. To a\ngreat extent the comparatively slow advance of biological sciences is\ndue to this very fact: the unalterable specific nature of biological\nmaterial.\n\nBut there is still another feature of biology dependent on the same\nfact. If a science is tied down to specific objects in every path it\ntakes, it first, of course, has to know all about those objects, and\nthat requires nothing else but plain description. We now understand why\npure description, in the most simple sense of the word, takes up such an\nenormous part of every text-book of biological science. It is not only\nmorphology, the science of form, that is most actively concerned with\ndescription; physiology also, in its present state, is pure description\nof what the functions of the different parts of the body of animals and\nplants actually *are*, at least for about nine-tenths of its range. It\nseems to me important to press this point very emphatically, since we\noften hear that physiology is from the very beginning a much higher sort\nof knowledge than morphology, inasmuch as it is rational. That is not at\nall true of the beginning of physiology: what the functions of the liver\nor of the root are has simply to be described just as the organisation\nof the brain or of the leaf, and it makes no difference logically that\none species of description has to use the experimental method, while the\nother has not. The experiment which only discovers what happens here or\nwhat happens there, possesses no kind of logical superiority over pure\ndescription at all.\n\nBut there will be another occasion in our lectures to deal more fully\nwith the logic of experiment and with the differences of descriptive\nknowledge and real rational science.\n\n\nTHE THREE DIFFERENT TYPES OF KNOWLEDGE ABOUT NATURE\n\nNatural sciences cannot originate before the given phenomena of nature\nhave been investigated in at least a superficial and provisional manner,\nby and for the practical needs of man. But as soon as true science\nbegins in any limited field, dealing, let us say, with animals or with\nminerals, or with the properties of bodies, it at once finds itself\nconfronted by two very different kinds of problems, both of them--like\nall \u201cproblems\u201d--created in the last resort by the logical organisation\nof the human mind, or, to speak still more correctly, of the Ego.\n\nIn any branch of knowledge which practical necessities have separated\nfrom others, and which science now tries to study methodically, there\noccur general sequences in phenomena, general orders of events. This\nuniformity is revealed only gradually, but as soon as it has shown\nitself, even in the least degree, the investigator seizes upon it. He\nnow devotes himself chiefly, or even exclusively, to the generalities in\nthe sequences of all changes. He is convinced that there must be a sort\nof most general and at the same time of most universal connection about\nall occurrences. This most universal connection has to be found out; at\nleast it will be the ideal that always will accompany the inquiring mind\nduring its researches. The \u201claw of nature\u201d is the ideal I am speaking\nabout, an ideal which is nothing less than one of the postulates of the\npossibility of science at all.\n\nUsing for our purposes a word which has been already introduced into\nterminology by the philosopher Windelband, though in a somewhat\ndifferent sense, we shall call that part of every branch of natural\nsciences which regards the establishment of a law of nature as its\nideal, \u201cnomothetic,\u201d *i.e.* \u201claw-giving.\u201d\n\nBut while every natural science has its nomothetic side, it also has\nanother half of a very different kind. This second half of every natural\nscience does not care for the same general, the same universal, which\nis shown to us in every event in a different and specified kind: it\nis diversity, it is specification, that constitutes the subject of\nits interest. Its aim is to find a sufficient reason for the types of\ndiversities, for the types of specifications. So in chemistry there\nhas been found a systematic order in the long series of the compounds\nand of the elements; crystallography also has its different systems of\ncrystals, and so on.\n\nWe have already employed the word by which we shall designate this\nsecond half of every natural science: it is the \u201csystematic\u201d side of\nscience.\n\nNomothetic work on the one side and systematics on the other do, in\nfact, appear in every natural science, and besides them there are no\nother main parts. But \u201cscience\u201d as a whole stands apart from another\naspect of reality which is called \u201chistory.\u201d History deals with\nparticulars, with particular events at such and such a place, whilst\nscience always abstracts from the particular, even in its systematic\nhalf.[1]\n\n[1] Windelband (*Geschichte und Naturwissenschaft*, 3 Auflage, 1904)\ngives the name \u201cnomothetic\u201d to the whole of our \u201cscience\u201d and calls the\nmethod of history \u201cidiographic.\u201d We thought it better to establish three\nfundamental types of all possible branches of knowledge.\n\n\nGENERAL PLAN OF THESE LECTURES\n\nTurning now to a sort of short outline of what is to be discussed\nin the whole of our future lectures, this summer and next, it seems\nclear, without further analysis, that biology as a science has its\nnomothetic and its systematic part also; respiration and assimilation,\nfor instance, have proved to be types of natural laws among living\nphenomena, and that there is a \u201csystem\u201d of animals and plants is too\ncommonly known to require further explanation here. Therefore we might\nstudy first biological laws, and after that biological systematics, and\nin the third place perhaps biological history. But that would hardly\ncorrespond to the philosophical aims of our lectures: our chief object\nis not biology as a regular science, as treated in text-books and in\nordinary university lectures; our chief object is the Philosophy of the\nOrganism, as aided and supported by scientific biology. Therefore a\ngeneral acquaintance with biology must be assumed in these lectures, and\nthe biological materials must be arranged according to their bearing on\nfurther, that is on philosophical, analysis.\n\nThat will be done, not, of course, to the extent of my regarding every\none of my audience as a competent biologist; on the contrary, I shall\nexplain most fully all points of biology proper, and even of the most\nsimple and descriptive kind of biology, which serve as bases for\nphilosophical analysis. But I shall do so only if they indeed do serve\nas such bases. All our biology will be not for its own sake, but for the\nsake of philosophy.\n\nWhilst regarding the whole of the biological material with such aims,\nit seems to me best to arrange the properly scientific material which\nis to be the basis of my discussions, not along the lines which biology\nas an independent science would select,[2] but to start from the three\ndifferent kinds of fundamental phenomena which living bodies offer to\ninvestigation, and to attach all systematics exclusively to one of them.\nFor there will not be very much for philosophy to learn from biological\nsystematics at present.\n\n[2] See J. Arth. Thomson, *The Science of Life*, London, 1899.\n\nLife is unknown to us except in association with bodies: we only know\nliving bodies and call them organisms. It is the final object of all\nbiology to tell us what it ultimately means to say that a body is\n\u201cliving,\u201d and in what sorts of relation body and life stand one to the\nother.\n\nBut at present it is enough to understand the terms \u201cbody\u201d and \u201cliving\u201d\nin the ordinary and popular sense.\n\nRegarding living bodies in this unpretentious manner, and recollecting\nwhat the principal characters are of all bodies we know as living ones,\nwe easily find that there are three features which are never wanting\nwherever life in bodies occurs. All living bodies are specific as to\nform--they \u201chave\u201d a specific form, as we are accustomed to say. All\nliving bodies also exhibit metabolism; that is to say, they stand in a\nrelation of interchange of materials with the surrounding medium, they\ntake in and give out materials, but their form can remain unchanged\nduring these processes. And, in the last place, we can say that all\nliving bodies move; though this faculty is more commonly known among\nanimals only, even elementary science teaches the student that it also\nbelongs to plants.\n\nTherefore we may ask for \u201claws of nature\u201d in biology about form, about\nmetabolism, and about movements. In fact, it is according to this scheme\nthat we shall arrange the materials of the biological part of our\nlectures, though, as we cannot regard the three divisions as equally\nimportant in their bearing on our ultimate purposes, we shall not treat\nthem quite on equal terms. It will appear that, at least in the present\nstate of science, the problems of organic form and of organic movement\nhave come into much closer relation to philosophical analysis than have\nmost of the empirical data on metabolism.\n\nIt is *form* particularly which can be said to occupy the very centre\nof biological interest; at least it furnishes the foundation of all\nbiology. Therefore we shall begin our scientific studies with a full and\nthorough analysis of form. The science of living forms, later on, will\nafford us a key to study metabolism proper with the greatest advantage\nfor our philosophical aims, and therefore the physiology of what is\nusually called the vegetative functions will be to us a sort of appendix\nto our chapters on form; only the theory of a problematic \u201cliving\nsubstance\u201d and of assimilation in the most general meaning of the word\nwill be reserved for the philosophical part; for very good reasons,\nas I hope to show. But our chapters on the living forms will have yet\nanother appendix besides the survey of the physiology of metabolism.\nBiological systematics almost wholly rests on form, on \u201cmorphology\u201d; and\nwhat hitherto has been done on the metabolical side of their problems,\nconsists of a few fragments, which are far from being an equivalent to\nthe morphological system; though, of course it must be granted that,\nlogically, systematics, in our general meaning of the word, as the sum\nof problems about the typically different and the specific, may be\nstudied on the basis of each one of the principal characteristics of\nliving bodies, not only on that of their forms. Therefore, systematics\nis to be the second appendix to the chief part of our studies in\nmorphology, and systematics, in its turn, will later on lead us to\na short sketch of the historical side of biology, to the theory of\nevolution in its different forms, and to the logic of history in general.\n\nSo far will our programme be carried out during this summer. Next year\nthe theory of movements will conclude our merely scientific analysis,\nand the remaining part of the course next summer will be devoted to the\nphilosophy of living nature. I hope that nobody will be able to accuse\nour philosophy of resting on unsound foundations. But those of you, on\nthe other hand, who would be apt to regard our scientific chapters as a\nlittle too long compared with their philosophical results, may be asked\nto consider that a small clock-tower of a village church is generally\nless pretentious but more durable than the campanile of San Marco has\nbeen.\n\nIndeed, these lectures will afford more \u201cfacts\u201d to my hearers, than\nGifford Lectures probably have done, as a rule. But how could that\nbe otherwise on the part of a naturalist? Scientific facts are the\nmaterial that the philosophy of nature has to work with, but these\nfacts, unfortunately, are not as commonly known as historical facts,\nfor instance, generally are; and they must be known, in order that a\nphilosophy of the organism may be of any value at all, that it may be\nmore than a mere entertainment.\n\nGoethe once said, that even in so-called facts there is more \u201ctheory\u201d\nthan is usually granted; he apparently was thinking of what might be\ncalled the ultimate or the typical facts in science. It is with such\ntypical or ultimate facts, of course, that we must become acquainted if\nour future philosophy is to be of profit to us.\n\nCertainly, there would be nothing to prevent us from arranging our\nmaterials in a manner exactly the reverse of that which we shall adopt;\nwe could begin with a general principle about the organic, and could\ntry to deduce all its special features from that principle, and such a\nway perhaps would seem to be the more fascinating method of argument.\nBut though logical it would not be psychological, and therefore would\nbe rather unnatural. And thus our *most* general principle about the\norganic will not come on the scene before the eighteenth of these twenty\nlectures, although it is not a mere inference or deduction from the\nformer lectures: it will be a culmination of the whole, and we shall\nappreciate its value the better the more we know what that whole really\nis.\n\n\nGENERAL CHARACTER OF THE ORGANIC FORM\n\nOur programme of this year, it was said, is to be devoted wholly\nto organic forms, though one of its appendixes, dealing with some\ncharacteristics of the physiology of metabolism, will lead us on to a\nfew other phenomena. What then are the essentials of a living form, as\ncommonly understood even without a special study of biology?\n\nLiving bodies are not simple geometrical forms, not, like crystals,\nmerely a typical arrangement of surfaces in space, to be reduced\ntheoretically, perhaps, to an arrangement of molecules. Living bodies\nare typically combined forms; that is to say, they consist of simpler\nparts of different characters, which have a special arrangement with\nregard to one another; these parts have a typical form of their own and\nmay again be combinations of more simple different parts. But besides\nthat, living bodies have not always the same typically combined form\nduring the whole of their life: they become more complicated as they\ngrow older; they all begin from one starting point, which has little\nform at all, viz., the egg. So the living form may be called a \u201cgenetic\nform,\u201d or a form considered as a process, and therefore *morphogenesis*\nis the proper and adequate term for the science which deals with the\nlaws of organic forms in general; or, if you prefer not to use the\nsame word both for a science and for the subjects of that science, the\n*physiology of morphogenesis*.\n\nNow there are different branches of the physiology of morphogenesis or\nphysiology of form. We may study, and indeed we at first shall study,\nwhat are the laws of the morphogenetic processes leading from the egg\nto the adult: that may be properly called physiology of development.\nBut living forms are not only able to originate in one unchangeable\nway: they may restore themselves, if disturbed, and thus we get the\nphysiology of restoration or restitution as a second branch of the\nscience of morphogenesis. We shall draw very important data, some of the\nfoundations indeed of our philosophical discussions, from the study of\nsuch restitutions. Besides that, it is to them that our survey of the\nproblems of the physiology of metabolism is to be appended.\n\nLiving forms not only originate from the egg and are able to restore\nthemselves, they also may give origin to other forms, guaranteeing in\nthis way the continuity of life. The physiology of heredity therefore\nappears as the counterpart to those branches of the physiology of form\nwhich deal with individual form and its restitutions. And our discussion\non heredity may be followed by our second appendix to this chief section\non form, an appendix regarding the outlines of systematics, evolution\nand history.\n\nTheoretical considerations on biology generally start, or at least,\nused to start, from the evolution theory, discussing all other problems\nof the physiology of form by the way only, as things of secondary\nimportance. You see from our programme, that we shall go just the\nopposite way: evolution will come last of all, and will be treated\nshortly; but the morphogenesis of the individual will be treated very\nfully, and very carefully indeed.\n\nWhy then this deviation from what is the common practice? Because we do\nnot know very much about evolution at all, because in this field we are\njust at the very beginning of what deserves the name of exact knowledge.\nBut concerning individual morphogenesis we really know, even at present,\nif not very much, at least something, and that we know in a fairly exact\nform, aided by the results of experiments.\n\nAnd it will not be without its reward, if we restrict our aims in such a\nmanner, if we prefer to deal more fully with a series of problems, which\nmay seem at the first glance to be of less interest than others. After a\nfew lectures we shall find already that we may decide one very important\nquestion about life merely by an analysis of individual form production,\nand without any regard to problematic and doubtful parts of biology:\nthat we may decide the question, whether \u201clife\u201d is only a combination\nof chemical and physical events, or whether it has its elemental laws,\nlaws of its own.\n\nBut to prepare the road that is to lead to such results we first have\nto restrict our aims once more, and therefore the next lecture of this\ncourse, which eventually is to touch almost every concept of philosophy\nproper, will begin with the pure description of the individual\ndevelopment of the common sea-urchin.\n\n\n\n\nSECTION A\n\nTHE CHIEF RESULTS OF ANALYTICAL BIOLOGY\n\n\n\n\nPART I\n\nTHE INDIVIDUAL ORGANISM WITH REGARD TO FORM AND METABOLISM\n\n*A.* ELEMENTARY MORPHOGENESIS\n\n\nEVOLUTIO AND EPIGENESIS IN THE OLD SENSE\n\nThe organism is a specific body, built up by a typical combination\nof specific and different parts. It is implied in the words of this\ndefinition, that the organism is different, not only from crystals, as\nwas mentioned in the last lecture, but also from all combinations of\ncrystals, such as those called dendrites and others, which consist of a\ntypical arrangement of identical units, the nature of their combination\ndepending on the forces of every single one of their parts. For this\nreason dendrites, in spite of the typical features in their combination,\nmust be called aggregates; but the organism is not an aggregate even\nfrom the most superficial point of view.\n\nWe have said before, what must have been familiar to you already, that\nthe organism is not always the same in its individual life, that it\nhas its development, leading from simpler to more complicated forms of\ncombination of parts; there is a \u201cproduction of visible manifoldness\u201d\ncarried out during development, to describe the chief character of that\nprocess in the words of Wilhelm Roux. We leave it an open question in\nour present merely descriptive analysis, whether there was already a\n\u201cmanifoldness,\u201d in an invisible state, before development, or whether\nthe phrase \u201cproduction of manifoldness\u201d is to be understood in an\nabsolute sense.\n\nIt has not always been granted in the history of biology, and of\nembryology especially, that production of visible manifoldness is the\nchief feature of what is called an organism\u2019s embryology or ontogeny:\nthe eighteenth century is full of determined scientific battles over the\nquestion. One school, with Albert von Haller and Bonnet as its leading\nmen, maintained the view that there was no production of different parts\nat all in development, this process being a mere \u201cevolutio,\u201d that is,\na growth of parts already existing from the beginning, yes, from the\nvery beginning of life; whilst the other school, with C. F. Wolff and\nBlumenbach at its head, supported the opposite doctrine of so-called\n\u201cepigenesis,\u201d which has been proved to be the right one.\n\nTo some extent these differences of opinion were only the outcome of the\nrather imperfect state of the optical instruments of that period. But\nthere were also deeper reasons beyond mere difficulties of description;\nthere were theoretical convictions underlying them. It is *impossible*,\nsaid the one party, that there is any real production of new parts;\nthere *must* be such a production, said the other.\n\nWe ourselves shall have to deal with these questions of the theory of\norganic development; but at present our object is narrower, and merely\ndescriptive. It certainly is of great importance to understand most\nclearly that there actually *is* a \u201cproduction of visible manifoldness\u201d\nduring ontogenesis in the descriptive sense; the knowledge of the fact\nof this process must be the very foundation of all studies on the theory\nof development in any case, and therefore we shall devote this whole\nlecture to studies in merely descriptive embryology.\n\nBut descriptive embryology, even if it is to serve merely as an\ninstance of the universality of the fact of epigenesis, can only be\nstudied successfully with reference to a concrete case. We select the\ndevelopment of the common sea-urchin (*Echinus microtuberculatus*) as\nsuch a case, and we are the more entitled to select this organism rather\nthan another, because most of the analytical experimental work, carried\nout in the interests of a real theory of development, has been done\non the germs of this animal. Therefore, to know at least the outlines\nof the individual embryology of the Echinus may indeed be called the\n*conditio sine qua non* for a real understanding of what is to follow.\n\n\nTHE CELL[3]\n\n[3] E. B. Wilson, *The Cell in Development and Inheritance*, New York,\nMacmillan, 1896.\n\nYou are aware that all organisms consist of organs and that each of\ntheir organs has a different function: the brain, the liver, the eyes,\nthe hands are types of organs in animals, as are the leaves and the\npistils in plants.\n\nYou are also aware that, except in the lowest organisms, the so-called\nProtista, all organs are built up of cells. That is a simple fact of\nobservation, and I therefore cannot agree with the common habit of\ngiving to this plain fact the title of cell-\u201ctheory.\u201d There is nothing\ntheoretical in it; and, on the other hand, all attempts to conceive\nthe organism as a mere aggregate of cells have proved to be wrong. It\nis *the whole* that uses the cells, as we shall see later on, or that\nmay not use them: thus there is nothing like a \u201ccell-theory,\u201d even in a\ndeeper meaning of the word.\n\nThe cell may have the most different forms: take a cell of the skin, of\na muscle, of a gland, of the wood in plants as typical examples. But in\nevery case two parts may be distinguished in a cell: an outside part,\nthe protoplasm, and an inside part, the nucleus, to leave out of special\naccount several others, which, by the way, may only be protoplasmatic\nmodifications.\n\nProtoplasm is a mere name for what is not the nucleus; in any case it is\nnot a homogeneous chemical compound; it consists of many such compounds\nand has a sort of architecture; all organic functions are based upon\nits metabolism. The nucleus has a very typical structure, which stands\nin a close relation to its behaviour during the most characteristic\nmorphological period of the cell: during its division. Let us devote a\nfew words to a consideration of this division and the part the nucleus\nplays in it; it will directly bear on future theoretical considerations\nabout development.\n\nThere is a certain substance in every nucleus of a cell which stains\nmost markedly, whenever cells are treated with pigments: the name\nof \u201cchromatin\u201d has been given to it. The chromatin always gives the\nreaction of an acid, while protoplasm is basic; besides that it seems to\nbe a centre of oxidation. Now, when a division of a cell is to occur,\nthe chromatin, which had been diffusely distributed before, in the form\nof small grains, arranges itself into a long and very much twisted\nthread. This thread breaks, as it were by sections, into almost equal\nparts, typical in number for each species, and each of these parts is\nsplit at full length. A certain number of pairs of small threads, the\nso-called \u201cchromosomes,\u201d are the ultimate result of this process, which\nintentionally has been described a little schematically, the breaking\nand the splitting in fact going on simultaneously or occasionally even\nin reverse order. While what we have described is performing in the\nnucleus, there have happened some typical modifications in protoplasm,\nand then, by an interaction of protoplasmatic and nuclear factors, the\nfirst step in the actual division of the cell begins. Of each pair of\nthe small threads of chromatin one constituent is moved to one side of\nthe cell, one to the other; two daughter-nuclei are formed in this way;\nthe protoplasm itself at the same time forms a circular furrow between\nthem; the furrow gets deeper and deeper; at last it cuts the cell in\ntwo, and the division of the cell is accomplished.\n\nNot only is the growth of the already typically formed organism carried\nout by a series of cell-divisions, but also development proper in our\nsense, as a \u201cproduction of visible manifoldness,\u201d is realised to a great\nextent by the aid of such divisions, which therefore may indeed be said\nto be of very fundamental importance (Fig. 1).\n\n[Illustration: Fig. 1.--Diagram of Cell-Division (*after* Boveri).\n\n*a.* Resting cell; the chromatin distributed in the form of small\ngranules inside the nucleus. Outside the nucleus is the \u201ccentrosome,\u201d\nnot mentioned in the text.\n\n*b.* Beginning of division; the chromatin arranged in the form of a long\nthread. Centrosome divided in two.\n\n*c.* The thread of chromatin cut into four parts, the \u201cchromosomes.\u201d\n\n*d.* The four parts of the chromatin arranged symmetrically between the\ncentrosomes and the star-like \u201cspheres.\u201d\n\n*e.* Each of the chromosomes split at full length.\n\n*f.* Beginning of division of protoplasm; the two parts of each\nchromosome separated.\n\n*g.* End of cell-division.]\n\nEach cell-division which promotes growth is followed by the\nenlargement of the two daughter-cells which result from it; these two\ndaughter-elements attain the exact size of the mother-cell before\ndivision, and as soon as this size is reached a new division begins:\nso the growth of the whole is in the main the result of the growth of\nthe elements. Cell-divisions during real organ-formation may behave\ndifferently, as will be described at a proper occasion.\n\n\nTHE EGG: ITS MATURATION AND FERTILISATION\n\nWe know that all the organs of an animal or plant consist of cells, and\nwe know what acts a cell can perform. Now there is one very important\norgan in all living beings, which is devoted to reproduction. This\norgan, the so-called ovary in animals, is also built up of cells,\nand its single cells are called the eggs; the eggs originated by\ncell-division, and cell-division is to lead from them to the new adult.\n\nBut, with a very few exceptions, the egg in the ovary is not able to\naccomplish its functions, unless certain typical events have occurred,\nsome of which are of a merely preparatory kind, whilst the others are\nthe actual stimulus for development.\n\nThe preparatory ones are generally known under the name of \u201cmaturation.\u201d\nThe egg must be \u201cmature,\u201d in order that it may begin development, or\neven that it may be stimulated to it. Maturation consists of a rather\ncomplicated series of phenomena: later on we shall have occasion to\nmention, at least shortly, what happens in the protoplasm during its\ncourse; as to the nuclear changes during maturation it may be enough\nfor our purposes to say, that there occur certain processes among the\nchromosomes, which lead to an extension of half of them in the form\nof two very small cells, the \u201cdirective cells\u201d or \u201cdirective or polar\nbodies,\u201d as they have been somewhat cautiously called.\n\nThe ripe or mature egg is capable of being fertilised.\n\nBefore turning to this important fact, which, by the way, will bring us\nto our specially chosen type, the Echinus, a few words may be devoted to\nthe phenomenon of \u201cparthenogenesis,\u201d that is to say, the possibility\nof development without fertilisation, since owing to the brilliant\ndiscoveries of the American physiologist, Jacques Loeb, this topic forms\none of the centres of biological interest at present. It has long been\nknown that the eggs of certain bees, lice, crayfishes, and other animals\nand also plants, are capable of development without fertilisation at\nall. Now Richard Hertwig and T. H. Morgan already had shown, that at\nleast nuclear division may occur in the eggs of other forms--in the egg\nof the sea-urchin for instance--when these eggs are exposed to some\nchemical injuries. But Loeb[4] succeeded in obtaining a full development\nby treating the eggs of echinoderms with chloride of magnesium; thus\nartificial parthenogenesis had been discovered. Later researches have\nshown that artificial parthenogenesis may occur in all classes of the\nanimal kingdom and may be provoked by all sorts of chemical or physical\nmeans. We do not know at present in what the proper stimulus consists\nthat must be supposed here to take the place of fertilisation; it seems,\nof course, highly probable that it is always the same in the last\nresort.[5]\n\n[4] *Amer. Journ. Physiol.* vols. iii. and iv. 1900.\n\n[5] According to Delage (*Arch. Zool. exp.*, 3 s\u00e9r. 10, 1902), it is\nindifferent for the realisation of artificial parthenogenesis, whether\nbut one, or both, or neither of the \u201cpolar bodies\u201d has been formed. But\nthe egg must be in the first stages of maturation to the extent that the\n\u201cnuclear membrane\u201d must be already dissolved.\n\nBut enough about processes, which at present are of a highly scientific,\nbut hardly of any philosophic interest.\n\nBy fertilisation proper we understand the joining of the male element,\nthe spermatozoon or the spermia, with the female element, the egg. Like\nthe egg, the spermatozoon is but a cell, though the two differ very much\nfrom one another in the relation between their protoplasm and nucleus:\nin all eggs it is the protoplasm which is comparatively very large, if\nheld together with somatic cells, in the spermatozoon it is the nucleus.\nA large amount of reserve material, destined for the growth of the\nfuture being, is the chief cause of the size of the egg-protoplasm. The\negg is quite or almost devoid of the faculty of movement, while on the\ncontrary, movement is the most typical feature of the spermia. Its whole\norganisation is adapted to movement in the most characteristic manner:\nindeed, most spermatozoa resemble a swimming infusorium, of the type\nof Flagellata, a so-called head and a moving tail are their two chief\nconstituents; the head is formed almost entirely of nuclear substance.\n\nIt seems that in most cases the spermatozoa swim around at random and\nthat their union with the eggs is assured only by their enormous number;\nonly in a few cases in plants have there been discovered special stimuli\nof a chemical nature, which attract the spermia to the egg.\n\nBut we cannot enter here more fully into the physiology of\nfertilisation, and shall only remark that its real significance is by no\nmeans clear.[6]\n\n[6] The older theories, attributing to fertilisation (or to\n\u201cconjugation,\u201d *i.e.* its equivalent in Protozoa), some sort of\n\u201crenovation\u201d or \u201crejuvenescence\u201d of the race, have been almost\ncompletely given up. (See Calkins, *Arch. f\u00fcr Entwickelungsmechanik*,\nxv. 1902). R. Hertwig recently has advocated the view, that abnormal\nrelations between the amounts of nuclear and of protoplasmatic material\nare rectified in some way by those processes. Teleologically, sexual\nreproduction has been considered as a means of variability (Weismann),\nbut also as a means of preserving the type!\n\n\nTHE FIRST DEVELOPMENT PROCESS OF ECHINUS\n\nTurning now definitively to the special kind of organism, chosen of our\ntype, the common sea-urchin, we properly begin with a few words about\nthe absolute size of its eggs and spermatozoa. All of you are familiar\nwith the eggs of birds and possibly of frogs; these are abnormally\nlarge eggs, on account of the very high amount of reserve material they\ncontain. The almost spherical egg of our Echinus only measures about a\ntenth of a millimetre in diameter; and the head of the spermatozoon has\na volume which is only the four-hundred-thousandth part of the volume\nof the egg! The egg is about on the extreme limit of what can be seen\nwithout optical instruments; it is visible as a small white point. But\nthe number of eggs produced by a single female is enormous and may\namount to hundreds of thousands; this is one of the properties which\nrender the eggs of Echinus so very suitable for experimental research;\nyou can obtain them whenever and in any quantity you like; and,\nmoreover, they happen to be very clear and transparent, even in later\nstages, and to bear all kinds of operations well.\n\nThe spermia enters the egg, and it does so in the open water--another\nof the experimental advantages of our type. Only one spermia enters\nthe egg in normal cases, and only its head goes in, the tail is left\noutside. The moment that the head has penetrated the protoplasm of the\negg a thin membrane is formed by the latter. This membrane is very soft\nat first, becoming much stronger later on; it is very important for all\nexperimental work, that by shaking the egg in the first minutes of its\nexistence the membrane can easily be destroyed without any damage to the\negg itself.\n\nAnd now occurs the chief phenomenon of fertilisation: the nucleus of\nthe spermatozoon unites with the nucleus of the egg. When speaking of\nmaturation, we mentioned that half of the chromatin was thrown out of\nthe egg by that process: now this half is brought in again, but comes\nfrom another individual.\n\nIt is from this phenomenon of nuclear union as the main character of\nfertilisation that almost all theories of heredity assume their right to\nregard the nuclei of the sexual cells as the true \u201cseat\u201d of inheritance.\nLater on we shall have occasion to discuss this hypothesis from the\npoint of view of logic and fact.\n\nAfter the complete union of what are called the male and the female\n\u201cpronuclei,\u201d the egg begins its development; and this development, in\nits first steps, is simply pure cell-division. We know already the chief\npoints of this process, and need only add to what has been described,\nthat in the whole first series of the cell-divisions of the egg, or,\nto use the technical term, in the whole process of the \u201ccleavage\u201d or\n\u201csegmentation\u201d of it, there is never any growth of the daughter-elements\nafter each division, such as we know to occur after all cell-divisions\nof later embryological stages. So it happens, that during cleavage the\nembryonic cells become smaller and smaller, until a certain limit is\nreached; the sum of the volumes of all the cleavage cells together is\nequal to the volume of the egg.\n\nBut our future studies will require a more thorough knowledge of the\ncleavage of our Echinus; the experimental data we shall have to describe\nlater on could hardly be properly understood without such knowledge.\nThe first division plane, or, as we shall say, the first cleavage\nplane, divides the eggs into equal parts; the second lies at right\nangles to the first and again divides equally: we now have a ring of\nfour cells. The third cleavage plane stands at right angles to the\nfirst two; it may be called an equatorial plane, if we compare the egg\nwith a globe; it also divides equally, and so we now find two rings,\neach consisting of four cells, and one above the other. But now the\ncell-divisions cease to be equal, at least in one part of the egg: the\nnext division, which leads from the eight- to the sixteen-cell stage of\ncleavage, forms four rings, of four cells each, out of the two rings of\nthe eight-cell stage. Only in one half of the germ, in which we shall\ncall the upper one, or which we might call, in comparison with a globe,\nthe northern hemisphere, are cells of equal size to be found; in the\nlower half of the egg four very small cells have been formed at one\n\u201cpole\u201d of the whole germ. We call these cells the \u201cmicromeres,\u201d that\nis, the \u201csmall parts,\u201d on the analogy of the term \u201cblastomeres,\u201d that\nis, parts of the germ, which is applied to all the cleavage cells in\ngeneral. The place occupied by the micromeres is of great importance\nto the germ as a whole: the first formation of real organs will start\nfrom this point later on. It is sufficient thus fully to have studied\nthe cleavage of our Echinus up to this stage: the later cleavage stages\nmay be mentioned more shortly. All the following divisions are into\nequal parts; there are no other micromeres formed, though, of course,\nthe cells derived from the micromeres of the sixteen-cell stage always\nremain smaller than the rest. All the divisions are tangential; radial\ncleavages never occur, and therefore the process of cleavage ends at\nlast in the formation of one layer of cells, which forms the surface\nof a sphere; it is especially by the rounding-up of each blastomere,\nafter its individual appearance, that this real surface layer of cells\nis formed, but, of course, the condition, that no radial divisions\noccur, is the most important one in its formation. When 808 blastomeres\nhave come into existence the process of cleavage is finished; a sphere\nwith a wall of cells and an empty interior is the result. That only 808\ncells are formed, and not, as might be expected, 1024, is due to the\nfact that the micromeres divide less often than the other elements; but\nspeaking roughly, of course, we may say that there are ten steps of\ncleavage-divisions in our form; 1024 being equal to 2^{10}.\n\nWe have learned that the first process of development, the cleavage, is\ncarried out by simple cell-division. A few cases are known, in which\ncell-division during cleavage is accompanied by a specific migration of\nparts of the protoplasm in the interior of the blastomeres, especially\nin the first two or first four; but in almost all instances cleavage\nis as simple a process of mere division as it is in our sea-urchin.\nNow the second step in development, at least in our form, is a typical\nhistological performance: it gives a new histological feature to all\nof the blastomeres: they acquire small cilia on their outer side and\nwith these cilia the young germ is able to swim about after it has left\nits membrane. The germ may be called a \u201cblastula\u201d at this stage, as it\nwas first called by Haeckel, whose useful denominations of the first\nembryonic stages may conveniently be applied, even if one does not agree\nwith most, or perhaps almost all, of his speculations (Fig. 2).\n\n[Illustration: Fig. 2.--Early Development of Echinus, the Common\nSea-urchin.\n\n*a.* Two cells.\n\n*b.* Four cells.\n\n*c.* Eight cells, arranged in two rings of four, above one another.\n\n*d.* Sixteen cells, four \u201cmicromeres\u201d formed at the \u201cvegetative\u201d pole.\n\n*e.* Optical section of the \u201cblastula,\u201d a hollow sphere consisting of\nabout one thousand cells, each of them with a small cilium.]\n\nIt is important to notice that the formation of the \u201cblastula\u201d from the\nlast cleavage stage is certainly a process of organisation, and may also\nbe called a differentiation with regard to that stage. But there is in\nthe blastula no trace of one *part* of the germ becoming different with\nrespect to others of its parts. If development were to go on in this\ndirection alone, high organisatory complications might occur: but there\nwould always be only one sort of cells, arranged in a sphere; there\nwould be only one kind of what is called \u201ctissue.\u201d\n\nBut in fact development very soon loads to true differences of the\nparts of the germ with respect to one another, and the next step of the\nprocess will enable us to apply different denominations to the different\nparts of the embryo.\n\nAt one pole of the swimming blastula, exactly at the point where the\ndescendants of the micromeres are situated, about fifty cells lose\ncontact with their neighbours and leave the surface of the globe, being\ndriven into the interior space of it. Not very much is known about the\nexact manner in which these changes of cellular arrangement are carried\nout, whether the cells are passively pressed by their neighbours, or\nwhether, perhaps, in a more active manner, they change their surface\nconditions; therefore, as in most ontogenetic processes, the description\nhad best be made cautiously in fairly neutral or figurative words.\n\nThe cells which in the above manner have entered the interior of the\nblastula are to be the foundation of important parts of the future\norganism; they are to form its connective tissue, many of its muscles,\nand the skeleton. \u201cMesenchyme,\u201d *i.e.* \u201cwhat has been infused into the\nother parts,\u201d is the technical name usually applied to these cells.\nWe now have to learn their definite arrangement. At first they lie\nas a sort of heap inside the cell wall of the blastula, inside the\n\u201cblastoderm,\u201d *i.e.* skin of the germ. But soon they move from one\nanother, to form a ring round the pole at which they entered, and on\nthis ring a process takes place which has a very important bearing upon\nthe whole type of the organisation of the germ. You will have noticed\nthat hitherto the germ with regard to its symmetry has been a monaxial\nor radial formation; the cleavage stages and the blastula with its\nmesenchyme were forms with two different poles, lying at the ends of one\nsingle line, and round this line everything was arranged concentrically.\nBut now what is called \u201cbilateral symmetry\u201d is established; the\nmesenchyme ring assumes a structure which can be symmetrically divided\nonly by one plane, but divided in such a way, that one-half of it is the\nmirror image of the other. A figure shows best what has occurred, and\nyou will notice (Fig. 3) two masses of cells in this figure, which have\nthe forms of spherical triangles: it is in the midst of these triangles\nthat the skeleton of the larva *originates*. The germ had an upper and\na lower side before: it now has got an upper and lower, front and back,\n*right and left* half; it now has acquired that symmetry of organisation\nwhich our own body has; at least it has got it as far as its mesenchyme\nis concerned.\n\n[Illustration: Fig. 3.--Formation of Mesenchyme in Echinus.\n\n*a.* Outlines of blastula, side-view; mesenchyme forms a heap of cells\nat the \u201cvegetative\u201d pole.\n\n*a*_1. Heap of mesenchyme-cells from above.\n\n*b.* Mesenchyme-cells arranged in a ring round the vegetative pole.\n\n*c.* Mesenchyme-cells arranged in a bilateral-symmetrical figure;\nprimordia of skeleton in the midst of two spherical triangles.]\n\nWe leave the mesenchyme for a while and study another kind of\norganogenesis. At the very same pole of the germ where the mesenchyme\ncells originated there is a long and narrow tube of cell growing in,\nand this tube, getting longer and longer, after a few hours of growth\ntouches the opposite pole of the larva. The growth of this cellular tube\nmarks the beginning of the formation of the intestine, with all that\nis to be derived from it. The larva now is no longer a blastula, but\nreceives the name of \u201cgastrula\u201d in Haeckel\u2019s terminology; it is built\nup of the three \u201cgerm-layers\u201d in this stage. The remaining part of the\nblastoderm is called \u201cectoderm,\u201d or outer layer; the newly-formed tube,\n\u201cendoderm,\u201d or inner layer; while the third layer is the \u201cmesenchyme\u201d\nalready known to us.\n\nThe endoderm itself is a radial structure at first, as was the whole\ngerm in a former stage, but soon its free end bends and moves against\none of the sides of the ectoderm, against that side of it where the two\ntriangles of the mesenchyme are to be found also. Thus the endoderm\nhas acquired bilateral symmetry just as the mesenchyme before, and\nas in this stage the ectoderm also assumes a bilateral symmetry\nin its form, corresponding with the symmetrical relations in the\nendoderm and the mesenchyme, we now may call the whole of our larva a\nbilateral-symmetrical organisation.\n\nIt cannot be our task to follow all the points of organogenesis of\nEchinus in detail. It must suffice to state briefly that ere long a\nsecond portion of the mesenchyme is formed in the larva, starting from\nthe free end of its intestine tube; that the formation of the so-called\n\u201ccoelum\u201d occurs by a sort of splitting off from this same original\norgan; and that the intestine itself is divided into three parts of\ndifferent size and aspect by two circular sections.\n\nBut we must not, I think, dismiss the formation of the skeleton so\nquickly. I told you already that the skeleton has its first origin in\nthe midst of the two triangular cell-masses of the mesenchyme; but what\nare the steps before it attains its typical and complicated structure?\nAt the beginning a very small tetrahedron, consisting of carbonate of\ncalcium, is formed in each of the triangles; the four edges of the\ntetrahedron are produced into thin rods, and by means of a different\norganogenesis along each of these rods the typical formation of the\nskeleton proceeds. But the manner in which it is carried out is very\nstrange and peculiar. About thirty of the mesenchyme cells are occupied\nin the formation of skeleton substance on each side of the larva. They\nwander through the interior space of the gastrula--which at this stage\nis not filled with sea water but with a sort of gelatinous material--and\nwander in such a manner that they always come to the right places, where\na part of the skeleton is to be formed; they form it by a process of\nsecretion, quite unknown in detail; one of them forms one part, one the\nother, but what they form altogether, is one whole.\n\nWhen the formation of the skeleton is accomplished, the typical larva\nof our Echinus is built up; it is called the \u201cpluteus\u201d (Fig. 4). Though\nit is far from being the perfect adult animal, it has an independent\nlife of its own; it feeds and moves about and does not go through any\nimportant changes of form for weeks. But after a certain period of\nthis species of independent life as a \u201clarva,\u201d the changes of form it\nundergoes again are most fundamental: it must be transformed into the\nadult sea-urchin, as all of you know. There are hundreds and hundreds\nof single operations of organogenesis to be accomplished before that\nend is reached; and perhaps the strangest of all these operations is a\ncertain sort of growth, by which the symmetry of the animal, at least\nin certain of its parts--not in all of them--is changed again from\nbilateral to radial, just the opposite of what happened in the very\nearly stages.\n\n[Illustration: Fig. 4.--Larval Development of Echinus.\n\n*A.* The gastrula.\n\n*B.* Later stage, bilateral-symmetrical. Intestine begins to divide\ninto three parts.\n\n*C.* Pluteus larva. S = Skeleton. I = Intestine.]\n\nBut we cannot follow the embryology of our Echinus further here; and\nindeed we are the less obliged to do so, since in all our experimental\nwork we shall have to deal with it only as far as to the pluteus larva.\nIt is impossible under ordinary conditions to rear the germs up to the\nadult stages in captivity.\n\nYou now, I hope, will have a general idea at least of the processes\nof which the individual development of an animal consists. Of course\nthe specific features leading from the egg to the adult are different\nin each specific case, and, in order to make this point as clear as\npossible, I shall now add to our description a few words about what may\nbe called a comparative descriptive embryology.\n\n\nCOMPARATIVE EMBRYOLOGY\n\nEven the cleavage may present rather different aspects. There may be a\ncompact blastula, not one surrounded by only one layer of cells as in\nEchinus; or bilaterality may be established as early as the cleavage\nstage--as in many worms and in ascidians--and not so late as in Echinus.\nThe formation of the germ layers may go on in a different order and\nunder very different conditions: a rather close relative of our Echinus,\nfor instance, the starfish, forms first the endoderm and afterwards\nthe mesenchyme. In many cases there is no tube of cells forming the\n\u201cendoderm,\u201d but a flat layer of cells is the first foundation of all the\nintestinal organs: so it is in all birds and in the cuttlefish. And,\nas all of you know, of course, there are very many animal forms which\nhave no proper \u201clarval\u201d stage: there is one in the frog, the well-known\n\u201ctadpole,\u201d but the birds and mammals have no larvae; that is to say,\nthere is no special stage in the ontogeny of these forms which leads an\nindependent life for a certain time, as if it were a species by itself,\nbut all the ontogenetical stages are properly \u201cembryonic\u201d--the germ is\nalways an \u201cembryo\u201d until it becomes the perfect young organism. And you\nalso know that not all skeletons consist of carbonate of calcium, but,\nthat there are skeletons of silicates, as in Radiolaria, and of horny\nsubstance, as in many sponges. And, indeed, if we were to glance at the\ndevelopment of plants also, the differences would seem to us probably\nso great that all the similarities would seem to disappear.\n\nBut there are similarities, nevertheless, in all development, and we\nshall now proceed to examine what they are. As a matter of fact, it was\nespecially for their sake that we studied the ontogeny of a special\nform in such detail; one always sees generalities better if one knows\nthe specific features of at least one case. What then are the features\nof most general and far-reaching importance, which may be abstracted\nfrom the individual history of our sea-urchin, checked always by the\nteachings of other ontogenies, including those of plants?\n\n\nTHE FIRST STEPS OF ANALYTICAL MORPHOGENESIS\n\nIf we look back upon the long fight of the schools of embryologists in\nthe eighteenth century about the question whether individual development\nwas to be regarded as a real production of visible manifoldness or as\na simple growth of visibly pre-existing manifoldness, whether it was\n\u201cepigenesis\u201d or \u201cevolutio,\u201d there can be no doubt, if we rely on all\nthe investigations of the last hundred and fifty years, that, taken in\nthe descriptive sense, the theory of epigenesis is right. Descriptively\nspeaking there *is* a production of visible manifoldness in the course\nof embryology: that is our first and main result. Any one possessed of\nan average microscope may any day convince himself personally that it is\ntrue.\n\nIn fact, true epigenesis, in the descriptive sense of the term, does\nexist. One thing is formed \u201cafter\u201d the other; there is not a mere\n\u201cunfolding\u201d of what existed already, though in a smaller form; there is\nno \u201cevolutio\u201d in the old meaning of the word.\n\nThe word \u201cevolution\u201d in English usually serves to denote the theory of\ndescent, that is of a real relationship of all organisms. Of course we\nare not thinking here of this modern and specifically English meaning of\nthe Latin word *evolutio*. In its ancient sense it means to a certain\ndegree just the opposite; it says that there is no formation of anything\nnew, no transformation, but simply growth, and this is promoted not for\nthe race but for the individual. Keeping well in mind these historical\ndifferences in the meaning of the word \u201cevolutio,\u201d no mistakes, it seems\nto me, can occur from its use. We now shall try to obtain a few more\nparticular results from our descriptive study of morphogenesis, which\nare nevertheless of a general bearing, being real characteristics of\norganic individual development, and which, though not calculated of\nthemselves to further the problem, will in any case serve to prepare for\na more profound study of it.\n\nThe totality of the line of morphogenetic facts can easily be resolved\ninto a great number of distinct processes. We propose to call these\n\u201celementary morphogenetic processes\u201d; the turning in of the endoderm\nand its division into three typical parts are examples of them. If we\ngive the name \u201celementary organs\u201d to the distinct parts of every stage\nof ontogeny which are uniform in themselves and are each the result of\none elementary process in our sense, we are entitled to say that each\nembryological stage consists of a certain number of elementary organs.\nThe mesenchyme ring, the coelum, the middle-intestine, are instances of\nsuch organs. It is important to notice well that the word elementary is\nalways understood here with regard to visible morphogenesis proper and\ndoes not apply to what may be called elementary in the physiological\nsense. An elementary process in our sense is a very distinct act of\nform-building, and an elementary organ is the result of every one of\nsuch acts.\n\nThe elementary organs are typical with regard to their position and with\nregard to their histological properties. In many cases they are of a\nvery clearly different histological type, as for instance, the cells of\nthe three so-called germ-layers; and in other cases, though apparently\nalmost identical histologically, they can be proved to be different\nby their different power of resisting injuries or by other means. But\nthere are not as many different types of histological structure as there\nare typically placed organs: on the contrary there are many elementary\norgans of the same type in different typical parts of the organism, as\nall of you know to be the case with nerves and muscles. It will not be\nwithout importance for our future theory of development, carefully to\nnotice this fact, that specialisation in the *position* of embryonic\nparts is more strict than in their histology.\n\nBut elementary organs are not only typical in position and histology,\nthey are typical also with regard to their form and their relative size.\nIt agrees with what has been said about histology being independent of\ntypical position, that there may be a number of organs in an embryonic\nstage, all in their most typical positions, which though all possessing\nthe same histology, may have different forms or different sizes or\nboth: the single bones of the skeleton of vertebrates or of adult\nechinoderms are the very best instances of this most important feature\nof organogenesis. If we look back from elementary organs to elementary\nprocesses, the specialisation of the size of those organs may also be\nsaid to be the consequence of a typical duration of the elementary\nmorphogenetic process leading to them.[7]\n\n[7] The phrase \u201c*ceteris paribus*\u201d has to be added of course, as the\nduration of each single elementary morphogenetic process is liable to\nvary with the temperature and many other conditions of the medium.\n\nI hardly need to say, that the histology, form, and size of elementary\norgans are equally an expression of their present or future\nphysiological function. At least they prepare for this function by a\nspecific sort of metabolism which sets in very early.\n\nThe whole sequence of individual morphogenesis has been divided by some\nembryologists into two different periods; there is a first period,\nduring which the foundations of the organisation of the \u201ctype\u201d are\nlaid down, and a second period, during which the histo-physiological\nspecifications are modelled out (von Baer, G\u00f6tte, Roux). Such a\ndiscrimination is certainly justified, if not taken too strictly; but\nits practical application would encounter certain difficulties in many\nlarval forms, and also, of course, in all plants.\n\nOur mention of plants leads us to the last of our analytical results. If\nan animal germ proceeds in its development from a stage *d* to the stage\n*g*, passing through *e* and *f*, we may say that the whole of *d* has\nbecome the whole of *f*, but we cannot say that there is a certain part\nof *f* which is *d*, we cannot say that *f* is *d* + *a*. But in plants\nwe can: the stage *f* is indeed equal to *a* + *b* + *c* + *d* + *e* +\n*a* [Transcriber\u2019s note: probable typo for *f*] in vegetable organisms;\nall earlier stages are actually visible as parts of the last one. The\ngreat embryologist, Carl Ernst von Baer, most clearly appreciated these\nanalytical differences between animal and vegetable morphogenesis. They\nbecome a little less marked if we remember that plants, in a certain\nrespect, are not simple individuals but colonies, and that among the\ncorals, hydroids, bryozoa, and ascidia, we find analogies to plants in\nthe animal kingdom; but nevertheless the differences we have stated are\nnot extinguished by such reasoning. It seems almost wholly due to the\noccurrence of so many foldings and bendings and migrations of cells and\ncomplexes of cells in animal morphogenesis, that an earlier stage of\ntheir development seems *lost* in the later one; those processes are\nalmost entirely wanting in plants, even if we study their very first\nontogenetic stages. If we say that almost all production of surfaces\ngoes on outside in plants, inside in animals, we shall have adequately\ndescribed the difference. And this feature again leads to the further\ndiversity between animals and plants which is best expressed by calling\nthe former \u201cclosed,\u201d the latter \u201copen\u201d forms: animals reach a point\nwhere they are finished, plants never are finished, at least in most\ncases.\n\nI hope you will allow that I have tried to draw from descriptive and\ncomparative embryology as many general analytical results as are\npossibly to be obtained. It is not my fault if there are not any\nmore, nor is it my fault if the results reached are not of the most\nsatisfactory character. You may say that these results perhaps enable\nyou to see a little more clearly and markedly than before a few of the\ncharacters of development, but that you have not really learnt anything\nnew. Your disappointment--my own disappointment--in our analysis is due\nto the use of pure description and comparison as scientific methods.\n\n\nTHE LIMITS OF PURE DESCRIPTION IN SCIENCE\n\nWe have analysed our descriptions as far as we could, and now we must\nconfess that what we have found cannot be the last thing knowable\nabout individual morphogenesis. There must be something deeper to be\ndiscovered: we only have been on the surface of the phenomena, we\nnow want to get to the very bottom of them. Why then occurs all that\nfolding, and bending, and histogenesis, and all the other processes we\nhave described? There must be something that drives them out, so to say.\n\nThere is a very famous dictum in the *Treatise on Mechanics* by the\nlate Gustav Kirchhoff, that it is the task of mechanics to describe\ncompletely and in the most simple manner all the motions that occur in\nnature. These words, which may appear problematic even in mechanics,\nhave had a really pernicious influence on biology. People were extremely\npleased with them. \u201c\u2018Describing\u2019--that is just what we always have\ndone,\u201d they said; \u201cnow we see that we have done just what was right;\na famous physicist has told us so.\u201d They did not see that Kirchhoff\nhad added the words \u201ccompletely and in the most simple manner\u201d; and\nmoreover, they did not consider that Kirchhoff never regarded it as the\nultimate aim of physics to describe thunderstorms or volcanic eruptions\nor denudations; yet it only is with such \u201cdescriptions\u201d that biological\ndescriptions of *given* bodies and processes are to be compared!\n\nPhysicists always have used both experiment and hypothetical\nconstruction--Kirchhoff himself did so in the most gifted manner. With\nthese aids they have gone through the whole of the phenomena, and what\nthey found to be ultimate and truly elemental, that alone may they\nbe said to have \u201cdescribed\u201d; but they have \u201cexplained\u201d by the aid of\nelementalities what proved to be not elemental in itself.[8]\n\n[8] We shall not avoid in these lectures the word \u201cexplain\u201d--so much\nout of fashion nowadays. To \u201cexplain\u201d means to subsume under known\nconcepts, or rules, or laws, or principles, whether the laws or concepts\nthemselves be \u201cexplained\u201d or not. Explaining, therefore, is always\nrelative: what is elemental, of course, is only to be described, or\nrather to be stated.\n\nIt is the *method* of the physicists--not their results--that\nmorphogenesis has to apply in order to make progress; and this method\nwe shall begin to apply in our next lectures. Physiology proper has\nnever been so short-sighted and self-satisfied as not to learn from\nother sciences, from which indeed there was very much to be learned; but\nmorphology has: the bare describing and comparing of descriptions has\nbeen its only aim for about forty years or more, and lines of descent of\na very problematic character were its only general results. It was not\nseen that science had to begin, not with problematic events of the past,\nbut with what actually happens before our eyes.\n\nBut before saying any more about the exact rational and experimental\nmethod in morphology, which indeed may be regarded as a new method,\nsince its prevalence in the eighteenth century had been really\nforgotten, we first shall have to analyse shortly some general attempts\nto understand morphogenesis by means of hypothetic construction\nexclusively. Such attempts have become very important as points of\nissue for really exact research, and, moreover, they deserve attention,\nbecause they prove that their authors at least had not quite forgotten\nthat there were still other problems to be solved in morphology than\nonly phylogenetical ones.\n\n\n\n\n*B.* EXPERIMENTAL AND THEORETICAL MORPHOGENESIS\n\n1. THE FOUNDATIONS OF THE PHYSIOLOGY OF DEVELOPMENT. \u201cEVOLUTIO\u201d AND\n\u201cEPIGENESIS\u201d\n\n\nTHE THEORY OF WEISMANN\n\nOf all the purely hypothetic theories on morphogenesis that of August\nWeismann[9] can claim to have had the greatest influence, and to\nbe at the same time the most logical and the most elaborated. The\n\u201cgerm-plasma\u201d theory of the German author is generally considered as\nbeing a theory of heredity, and that is true inasmuch as problems of\ninheritance proper have been the starting-point of all his hypothetic\nspeculations, and also form in some respect the most valuable part\nof them. But, rightly understood, Weismann\u2019s theory consists of two\nindependent parts, which relate to morphogenesis and to heredity\nseparately, and it is only the first which we shall have to take into\nconsideration at present; what is generally known as the doctrine of the\n\u201ccontinuity of the germ-plasm\u201d will be discussed in a later chapter.\n\n[9] *Das Keimplasma*, Jena, 1892.\n\nWeismann assumes that a very complicated organised structure, below\nthe limits of visibility even with the highest optical powers, is the\nfoundation of all morphogenetic processes, in such a way that, whilst\npart of this structure is handed over from generation to generation as\nthe basis of heredity, another part of it is disintegrated during the\nindividual development, and directs development by being disintegrated.\nThe expression, \u201cpart\u201d of the structure, first calls for some\nexplanation. Weismann supposes several examples, several copies, as it\nwere, of his structure to be present in the germ cells, and it is to\nthese copies that the word \u201cpart\u201d has been applied by us: at least one\ncopy has to be disintegrated during ontogeny.\n\nThe morphogenetic structure is assumed to be present in the nucleus\nof the germ cells, and Weismann supposes the disintegration of his\nhypothetic structure to be accomplished by nuclear division. By the\ncleavage of the egg, the most *fundamental* parts of it are separated\none from the other. The word \u201cfundamental\u201d must be understood as\napplying not to proper elements or complexes of elements of the\norganisation, but to the chief relations of symmetry; the first\ncleavage, for instance, may separate the right and the left part of\nthe structure, the second one its upper and lower parts, and after the\nthird or equatorial cleavage all the principal eighths of our minute\norganisation are divided off: for the minute organisation, it must now\nbe added, had been supposed to be built up differently in the three\ndirections of space, just as the adult organism is. Weismann concedes it\nto be absolutely unknown in what manner the proper relation between the\nparts of the disintegrated fundamental morphogenetic structure and the\nreal processes of morphogenesis is realised; enough that there may be\nimagined such a relation.\n\nAt the end of organogenesis the structure is assumed to have been\nbroken up into its elements, and these elements, which may be chemical\ncompounds, determine the fate of the single cells of the adult organism.\n\nHere let us pause for a moment. There cannot be any doubt that\nWeismann\u2019s theory resembles to a very high degree the old \u201cevolutio\u201d\ndoctrines of the eighteenth century, except that it is a little less\ncrude. The chick itself is not supposed to be present in the hen\u2019s egg\nbefore development, and ontogeny is not regarded as a mere growth of\nthat chick in miniature, but what really is supposed to be present in\nthe egg is nevertheless a something that in all its parts corresponds\nto all the parts of the chick, only under a somewhat different\naspect, while all the relations of the parts of the one correspond\nto the relations of the parts of the other. Indeed, only on such an\nhypothesis of a fairly fixed and rigid relation between the parts of\nthe morphogenetic structure could it be possible for the disintegration\nof the structure to go on, not by parts of organisation, but by parts\nof symmetry; which, indeed, is a very strange, but not an illogical,\nfeature of Weismann\u2019s doctrine.\n\nWeismann is absolutely convinced that there must be a theory of\n\u201cevolutio,\u201d in the old sense of the word, to account for the ontogenetic\nfacts; that \u201cepigenesis\u201d has its place only in descriptive embryology,\nwhere, indeed, as we know, manifoldness in the *visible* sense is\nproduced, but that epigenesis can never form the foundation of a real\nmorphogenetic *theory*: theoretically one pre-existing manifoldness is\ntransformed into the other. An epigenetic theory would lead right beyond\nnatural science, Weismann thinks, as in fact, all such theories, if\nfully worked out, have carried their authors to vitalistic views. But\nvitalism is regarded by him as dethroned for ever.\n\nUnder these circumstances we have a good right, it seems to me, to speak\nof a *dogmatic* basis of Weismann\u2019s theory of development.\n\nBut to complete the outlines of the theory itself: Weismann was\nwell aware that there were some grave difficulties attaching to his\nstatements: all the facts of so-called adventitious morphogenesis in\nplants, of regeneration in animals, proved that the morphogenetic\norganisation could not be fully disintegrated during ontogeny. But these\ndifficulties were not absolute: they could be overcome: indeed, Weismann\nassumes, that in certain specific cases--and he regarded all cases of\nrestoration of a destroyed organisation as due to specific properties\nof the subjects, originated by roundabout variations and natural\nselection--that in specific cases, specific arrangements of minute parts\nwere formed during the process of disintegration, and were surrendered\nto specific cells during development, from which regeneration or\nadventitious budding could originate if required. \u201cPlasma of reserve\u201d\nwas the name bestowed on these hypothetic arrangements.\n\nAlmost independently another German author, Wilhelm Roux,[10] has\nadvocated a theoretical view of morphogenesis which very closely\nresembles the hypothesis of Weismann. According to Roux a minute\nultimate structure is present in the nucleus of the germ and directs\ndevelopment by being divided into its parts during the series of nuclear\ndivisions.\n\n[10] *Die Bedeutung der Kernteilungsfiguren*, Leipzig, 1883.\n\nBut in spite of this similarity of the outset, we enter an altogether\ndifferent field of biological investigation on mentioning Roux\u2019s name:\nwe are leaving hypothetic construction, at least in its absoluteness,\nand are entering the realms of scientific experiment in morphology.\n\n\nEXPERIMENTAL MORPHOLOGY\n\nI have told you already in the last lecture that, while in the\neighteenth century individual morphogenesis had formed the centre of\nbiological interest and been studied experimentally in a thoroughly\nadequate manner, that interest gradually diminished, until at last\nthe physiology of form as an exact separate science was almost wholly\nforgotten. At least that was the state of affairs as regards zoological\nbiology; botanists, it must be granted, have never lost the historical\ncontinuity to such a degree; botany has never ceased to be regarded\nas one science and never was broken up into parts as zoology was.\nZoological physiology and zoological morphology indeed were for many\nyears in a relationship to one another not very much closer than the\nrelation between philology and chemistry.\n\nThere were always a few men, of course, who strove against the current.\nThe late Wilhelm His,[11] instance, described the embryology of the\nchick in an original manner, in order to find out the mechanical\nrelations of embryonic parts, by which passive deformation, as an\nintegrating part of morphogenesis, might be induced. He also most\nclearly stated the ultimate aim of embryology to be the mathematical\nderivation of the adult form from the distribution of growth in the\ngerm. To Alexander Goette[12] we owe another set of analytical\nconsiderations about ontogeny. Newport, as early as 1850, and in\nlater years Pfl\u00fcger and Rauber, carried out experiments on the eggs\nof the frog, which may truly be called anticipatory of what was to\nfollow. But it was Wilhelm Roux,[13] now professor of anatomy at\nHalle, who entered the field with a thoroughly elaborated programme,\nwho knew not only how to state the problem analytically, but also\nhow to attack it, fully convinced of the importance of what he did.\n\u201cEntwickelungsmechanik,\u201d--mechanics of development--he called the \u201cnew\nbranch of anatomical science\u201d of which he tried to lay the foundations.\n\n[11] *Unsere K\u00f6rperform*, Leipzig, 1875.\n\n[12] *Die Entwickelungsgeschichte der Unke*, Leipzig, 1875.\n\n[13] *Gesammelte Abhandlungen*, Leipzig, 1895. Most important\ntheoretical papers:--*Zeitschr. Biolog.* 21, 1885; *Die\nEntwickelungsmechanik der Organismen*, Wien, 1890; *Vortr\u00e4ge und\nAufs\u00e4tze \u00fcber Entwickelungsmechanik*, Heft i., Leipzig, 1905.\n\nI cannot let this occasion pass without emphasising in the most decided\nmanner how highly in my opinion Roux\u2019s services to the systematic\nexploration of morphogenesis must be esteemed. I feel the more obliged\nto do so, because later on I shall have to contradict not only many\nof his positive statements but also most of his theoretical views. He\nhimself has lately given up much of what he most strongly advocated only\nten years ago. But Roux\u2019s place in the history of biological science can\nnever be altered, let science take what path it will.\n\nIt is not the place here to develop the logic of experiment; least of\nall is it necessary in the country of John Stuart Mill. All of you know\nthat experiment, by its method of isolating the single constituents\nof complicated phenomena, is the principal aid in the discovery of\nso-called causal relations. Let us try then to see what causal\nrelations Wilhelm Roux established with the aid of morphogenetic\nexperiment.\n\n\nTHE WORK OF WILHELM ROUX\n\nWe know already that an hypothesis about the foundation of individual\ndevelopment was his starting-point. Like Weismann he supposed that\nthere exists a very complicated structure in the germ, and that nuclear\ndivision leads to the disintegration of that structure. He next tried to\nbring forward what might be called a number of indicia supporting his\nview.\n\nA close relation had been found to exist in many cases between the\ndirection of the first cleavage furrows of the germ and the direction\nof the chief planes of symmetry in the adult: the first cleavage, for\ninstance, very often corresponds to the median plane, or stands at right\nangles to it. And in other instances, such as have been worked out into\nthe doctrine of so-called \u201ccell-lineages,\u201d typical cleavage cells were\nfound to correspond to typical organs. Was not that a strong support\nfor a theory which regarded cellular division as the principal means\nof differentiation? It is true, the close relations between cleavage\nand symmetry did not exist in every case, but then there had always\nhappened some specific experimental disturbances, *e.g.* influences of\nan abnormal direction of gravity on account of a turning over of the\negg, and it was easy to reconcile such cases with the generally accepted\ntheory on the assumption of what was called \u201canachronism\u201d of cleavage.\n\nBut Roux was not satisfied with mere indicia, he wanted a proof, and\nwith this intention he carried out an experiment which has become\nvery celebrated.[14] With a hot needle he killed one of the first two\nblastomeres of the frog\u2019s egg after the full accomplishment of its first\ncleavage, and then watched the development of the surviving cell. A\ntypical half-embryo was seen to emerge--an organism indeed, which was as\nmuch a half as if a fully formed embryo of a certain stage had been cut\nin two by a razor. It was especially in the anterior part of the embryo\nthat its \u201chalfness\u201d could most clearly be demonstrated.\n\n[14] *Virchow\u2019s Archiv.* 114, 1888.\n\nThat seemed to be a proof of Weismann\u2019s and Roux\u2019s theory of\ndevelopment, a proof of the hypothesis that there is a very complicated\nstructure which promotes ontogeny by its disintegration, carried out\nduring the cell divisions of embryology by the aid of the process of\nnuclear division, the so-called \u201ckaryokinesis.\u201d\n\nTo the dispassionate observer it will appear, I suppose, that the\nconclusions drawn by Roux from his experiment go a little beyond their\nlegitimate length. Certainly some sort of \u201cevolutio\u201d is proved by\nrearing half the frog from half the egg. But is anything proved, is\nthere anything discovered at all about the nucleus? It was only on\naccount of the common opinion about the part it played in morphogenesis\nthat the nucleus had been taken into consideration.\n\nThings soon became still more ambiguous.\n\n\nTHE EXPERIMENTS ON THE EGG OF THE SEA-URCHIN\n\nRoux\u2019s results were published for the first time in 1888; three years\nlater I tried to repeat his fundamental experiment on another subject\nand by a somewhat different method. It was known from the cytological\nresearches of the brothers Hertwig and Boveri that the eggs of the\ncommon sea-urchin (*Echinus microtuberculatus*) are able to stand well\nall sorts of rough treatment, and that, in particular, when broken into\npieces by shaking, their fragments will survive and continue to segment.\nI took advantage of these facts for my purposes. I shook the germs\nrather violently during their two-cell stage, and in several instances I\nsucceeded in killing one of the blastomeres, while the other one was not\ndamaged, or in separating the two blastomeres from one another.[15]\n\n[15] *Zeitschr. wiss. Zool.* 53, 1891.\n\nLet us now follow the development of the isolated surviving cell. It\nwent through cleavage just as it would have done in contact with its\nsister-cell, and there occurred cleavage stages which were just half\nof the normal ones. The stage, for instance, which corresponded to the\nnormal sixteen-cell stage, and which, of course, in my subjects was\nbuilt up of eight elements only, showed two micromeres, two macromeres\nand four cells of medium size, exactly as if a normal sixteen-cell stage\nhad been cut in two; and the form of the whole was that of a hemisphere.\nSo far there was no divergence from Roux\u2019s results.\n\nThe development of our Echinus proceeds rather rapidly, the cleavage\nbeing accomplished in about fifteen hours. I now noticed on the evening\nof the first day of the experiment, when the half-germ was composed of\nabout two hundred elements, that the margin of the hemispherical germ\nbent together a little, as if it were about to form a whole sphere\nof smaller size, and, indeed, the next morning a *whole* diminutive\nblastula was swimming about. I was so much convinced that I should get\nRoux\u2019s morphogenetical result in all its features that, even in spite of\nthis whole blastula, I now expected that the next morning would reveal\nto me the half-organisation of my subject once more; the intestine, I\nsupposed, might come out quite on one side of it, as a half-tube, and\nthe mesenchyme ring might be a half one also.\n\nBut things turned out as they were bound to do and not as I had\nexpected; there was a typically *whole* gastrula on my dish the next\nmorning, differing only by its small size from a normal one; and this\n*small but whole* gastrula was followed by a whole and typical small\npluteus-larva (Fig. 5).\n\n[Illustration: Fig. 5.--Illustration of Experiments on Echinus.\n\n*a*_1 and *b*_1. Normal gastrula and normal pluteus.\n\n*a*_2 and *b*_2. \u201cHalf\u201d-gastrula and \u201chalf\u201d-pluteus, that *ought* to result\nfrom one of the first two blastomeres, when isolated, according to the\ntheory of \u201cevolutio.\u201d\n\n*a*_3 and *b*_3. The small *but whole* gastrula and pluteus that actually\n*do* result.]\n\nThat was just the opposite of Roux\u2019s result: one of the first two\nblastomeres had undergone a half-cleavage as in his case, but then it\nhad become a whole organism by a simple process of rearrangement of its\nmaterial, without anything that resembled regeneration, in the sense of\na completion by budding from a wound.\n\nIf one blastomere of the two-cell stage was thus capable of performing\nthe morphogenetical process in its totality, it became, of course,\n*impossible* to allow that nuclear division had separated any sort of\n\u201cgerm-plasm\u201d into two different halves, and not even the protoplasm of\nthe egg could be said to have been divided by the first cleavage furrow\ninto unequal parts, as the postulate of the strict theory of so-called\n\u201cevolutio\u201d had been. This was a very important result, sufficient\nalone to overthrow at once the theory of ontogenetical \u201cevolutio,\u201d\nthe \u201cMosaiktheorie\u201d as it had been called--not by Roux himself, but\naccording to his views--in its exclusiveness.\n\nAfter first widening the circle of my observations by showing that\none of the first four blastomeres is capable of performing a whole\norganogenesis, and that three of the first four blastomeres together\nresult in an absolutely perfect organism, I went on to follow up\nseparately one of the two fundamental problems which had been suggested\nby my first experiment: was there anything more to find out about\nthe importance or unimportance of the single *nuclear* divisions in\nmorphogenesis?[16]\n\n[16] *Zeitschr. wiss. Zool.* 55, 1892.\n\nBy raising the temperature of the medium or by diluting the sea-water to\na certain degree it proved at first to be possible to alter in a rather\nfundamental way the type of the cleavage-stages without any damage to\nthe resulting organism. There may be no micromeres at the sixteen-cell\nstage, or they may appear as early as in the stage of eight cells;\nno matter, the larva is bound to be typical. So it certainly is not\nnecessary for all the cleavages to occur just in their normal order.\n\nBut of greater importance for our purposes was what followed. I\nsucceeded in pressing the eggs of Echinus between two glass plates,\nrather tightly, but without killing them; the eggs became deformed to\ncomparatively flat plates of a large diameter. Now in these eggs all\nnuclear division occurred at right angles to the direction of pressure,\nthat is to say, in the direction of the plates, as long as the pressure\nlasted; but the divisions began to occur at right angles to their former\ndirection, as soon as the pressure ceased. By letting the pressure be\nat work for different times I therefore, of course, had it quite in my\npower to obtain cleavage types just as I wanted to get them. If, for\ninstance, I kept the eggs under pressure until the eight-cell stage was\ncomplete, I got a plate of eight cells one beside the other, instead of\ntwo rings, of four cells each, one above the other, as in the normal\ncase; but the next cell division occurred at right angles to the former\nones, and a sixteen-cell stage, of two plates of eight cells each, one\nabove the other, was the result. If the pressure continued until the\nsixteen-cell stage was reached, sixteen cells lay together in one plate,\nand two plates of sixteen cells each, one above the other, were the\nresult of the next cleavage.\n\nWe are not, however, studying these things for cytological, but for\nmorphogenetical purposes, and for these the cleavage phenomenon itself\nis less important than the organogenetic result of it: all our subjects\nresulted in *absolutely normal* organisms. Now, it is clear, that the\nspatial relations of the different nuclear divisions to each other are\nanything but normal, in the eggs subjected to the pressure experiments;\nthat, so to say, every nucleus has got quite different neighbours if\ncompared with the \u201cnormal\u201d case. If that makes no difference, then\nthere *cannot* exist any close relation between the single nuclear\ndivisions and organogenesis at all, and the conclusion we have drawn\nmore provisionally from the whole development of isolated blastomeres\nhas been extended and proved in the most perfect manner. There ought to\nresult a morphogenetic chaos according to the theory of real \u201cevolutio\u201d\ncarried out by nuclear division, if the positions of the single nuclei\nwere fundamentally changed with regard to one another (Fig. 6). But now\nthere resulted not chaos, but the normal organisation: therefore it was\ndisproved in the strictest way that nuclear divisions have any bearing\non the origin of organisation; at least as far as the divisions during\ncleavage come into account.\n\n[Illustration: Fig. 6.--Pressure-experiments on Echinus.\n\n*a*_1 and *b*_1. Two normal cleavage stages, consisting of eight and\nsixteen cells.\n\n*a*_2 and *b*_2. Corresponding stages modified by exerting pressure\nuntil the eight-cell stage was finished. See text.]\n\nOn the egg of the frog (O. Hertwig), and on the egg of annelids (E. B.\nWilson), my pressure experiments have been carried out with the same\nresult.[17]\n\n[17] In the pressure experiments I had altered the relative position of\nthe nuclei *in origine*. In later years I succeeded in disturbing the\narrangement of the fully formed cells of the eight-cell stage, and in\ngetting normal larv\u00e6 in spite of that in many cases. But as this series\nof experiments is not free from certain complications--which in part\nwill be understood later on (see page 73)--it must suffice here to have\nmentioned them. (For further information see my paper in *Archiv. f.\nEntwickelungsmechanik*, xiv., 1902, page 500.)\n\n\nON THE INTIMATE STRUCTURE OF THE PROTOPLASM OF THE GERM\n\nNuclear division, as we have seen, cannot be the basis of organogenesis,\nand all we know about the whole development of isolated blastomeres\nseems to show that there exists nothing responsible for differentiation\nin the protoplasm either.\n\nBut would that be possible? It cannot appear possible on a more profound\nconsideration of the nature of morphogenesis, it seems to me: as the\nuntypical agents of the medium cannot be responsible in any way for\nthe origin of a form combination which is most typical and specific,\nthere must be somewhere in the egg itself a certain factor which is\nresponsible at least for the general orientation and symmetry of it.\nConsiderations of this kind led me, as early as 1893,[18] to urge the\nhypothesis that there existed, that there *must* exist, a sort of\nintimate structure in the egg, including polarity and bilaterality as\nthe chief features of its symmetry, a structure which belongs to every\nsmallest element of the egg, and which might be imagined by analogy\nunder the form of elementary magnets.[19] This hypothetic structure\ncould have its seat in the protoplasm only. In the egg of echinoderms it\nwould be capable of such a quick rearrangement after being disturbed,\nthat it could not be observed but only inferred logically; there might,\nhowever, be cases in which its real discovery would be possible. Indeed\nRoux\u2019s frog-experiment seems to be a case where it is found to be at\nwork: at least it seems very probable to assume that Roux obtained half\nof a frog\u2019s embryo because the protoplasm of the isolated blastomere had\npreserved the \u201chalfness\u201d of its intimate structure, and had not been\nable to form a small whole out of it.\n\n[18] *Mitteil. Neapel. 11, 1893.*\n\n[19] But the elementary magnets would have to be bilateral!\n\nOf course it was my principal object to verify this hypothesis, and\nsuch verification became possible in a set of experiments which my\nfriend T. H. Morgan and myself carried out together,[20] in 1895, on\nthe eggs of ctenophores, a sort of pelagic animals, somewhat resembling\nthe jelly-fish, but of a rather different inner organisation. The\nzoologist Chun had found even before Roux\u2019s analytical studies, that\nisolated blastomeres of the ctenophore egg behave like parts of the\nwhole and result in a half-organisation like the frog\u2019s germ does. Chun\nhad not laid much stress on his discovery, which now, of course, from\nthe new points of view, became a very important one. We first repeated\nChun\u2019s experiment and obtained his results, with the sole exception\nthat there was a tendency of the endoderm of the half-larva of Bero\u00eb\nto become more than \u201chalf.\u201d But that was not what we chiefly wanted to\nstudy. We succeeded in cutting away a certain mass of the protoplasm\nof the ctenophore egg just before it began to cleave, without damaging\nits nuclear material in any way: in all cases, where the cut was\nperformed at the side, there resulted a certain type of larvae from\nour experiments which showed exactly the same sort of defects as were\npresent in larvae developed from one of the first two blastomeres alone.\n\n[20] *Arch. Entw. Mech.* 2, 1895.\n\nThe hypothesis of the morphogenetic importance of *protoplasm* had thus\nbeen proved. In our experiments there was all of the nuclear material,\nbut there were defects on one side of the protoplasm of the egg; and the\ndefects in the adult were found to correspond to these defects in the\nprotoplasm.\n\nAnd now O. Schultze and Morgan succeeded in performing some experiments\nwhich directly proved the hypothesis of the part played by protoplasm\nin the subject employed by Roux, *viz.*, the frog\u2019s egg. The first of\nthese investigators managed to rear two whole frog embryos of small\nsize, if he slightly pressed the two-cell stage of that form between\ntwo plates of glass and turned it over; and Morgan,[21] after having\nkilled one of the first two blastomeres, as was done in the original\nexperiment of Roux, was able to bring the surviving one to a half or\nto a whole development according as it was undisturbed or turned.\nThere cannot be any doubt that in both of these cases, it is the\npossibility of a rearrangement of protoplasm, offered by the turning\nover, which allows the isolated blastomere to develop as a whole. The\nregulation of the frog\u2019s egg, with regard to its becoming whole, may be\ncalled facultative, whilst the same regulation of the egg of Echinus\nis obligatory. It is not without interest to note that the first two\nblastomeres of the common newt, *i.e.* of a form which belongs to the\nother class of Amphibia, after a separation of *any* kind, *always*\ndevelop as wholes, their faculty of regulation being obligatory, like\nthat of Echinus.\n\n[21] *Anat. Anz.* 10, 1895.\n\nWhole or partial development may thus be dependent on the power of\nregulation contained in the intimate polar-bilateral structure of the\nprotoplasm. Where this is so, the regulation and the differences in\ndevelopment are both connected with the chief relations of symmetry.\nThe development becomes a half or a quarter of the normal because\nthere is only one-half or one-quarter of a certain structure present,\none-half or one-quarter with regard to the very wholeness of this\nstructure; the development is whole, in spite of disturbances, if\nthe intimate structure became whole first. We may describe the\n\u201cwholeness,\u201d \u201chalfness,\u201d or \u201cquarterness\u201d of our hypothetic structure\nin a mathematical way, by using three axes, at right angles to one\nanother, as the base of orientation. To each of these, *x*, *y*, and\n*z*, a certain specific state with regard to the symmetrical relations\ncorresponds; thence it follows that, if there are wanting all those\nparts of the intimate structure which are determined, say, by a negative\nvalue of *y*, by minus *y*, then there is wanting half of the intimate\nstructure; and this halfness of the intimate structure is followed by\nthe halfness of organogenesis, the dependence of the latter on the\nintimate structure being established. But if regulation has restored,\non a smaller scale, the whole of the arrangement according to all values\nof *x*, *y* and *z*, development also can take place completely (Fig. 7).\n\n[Illustration: Fig. 7.--Diagram illustrating the intimate Regulation of\nProtoplasm from \u201cHalf\u201d to \u201cWhole.\u201d\n\nThe large circle represents the original structure of the egg. In all\ncases where cleavage-cells of the two-cell stage are isolated this\noriginal structure is only present as \u201chalf\u201d in the beginning, say\nonly on the right (+*y*) side. Development then becomes \u201chalf,\u201d if the\nintimate structure remains half; but it becomes \u201cwhole\u201d (on a smaller\nscale) if a new whole-structure (small circle!) is formed by regulatory\nprocesses.]\n\nI am quite aware that such a discussion is rather empty and purely\nformal, nevertheless it is by no means without value, for it shows\nmost clearly the differences between what we have called the intimate\nstructure of germs, responsible only for the general symmetry of\nthemselves and of their isolated parts, and another sort of possible\nstructure of the egg-protoplasm which we now shall have to consider, and\nwhich, at the first glance, seems to form a serious difficulty to our\nstatements, as far at least as they claim to be of general importance.\nThe study of this other sort of germinal structure at the same time will\nlead us a step farther in our historical sketch of the first years of\n\u201cEntwickelungsmechanik\u201d and will bring this sketch to its end.\n\n\nON SOME SPECIFICITIES OF ORGANISATION IN CERTAIN GERMS\n\nIt was known already about 1890, from the careful study of what has\nbeen called \u201ccell-lineage,\u201d that in the eggs of several families of\nthe animal kingdom the origin of certain organs may be traced back to\nindividual cells of cleavage, having a typical histological character\nof their own. In America especially such researches have been carried\nout with the utmost minuteness, E. B. Wilson\u2019s study of the cell-lineage\nof the Annelid *Nereis* being the first of them. If it were true that\nnuclear division is of no determining influence upon the ontogenetic\nfate of the blastomeres, only peculiarities of the different parts of\nthe protoplasm could account for such relations of special cleavage\ncells to special organs. I advocated this view as early as in 1894,\nand it was proved two years later by Crampton, a pupil of Wilson\u2019s,\nin some very fine experiments performed on the germ of a certain\nmollusc.[22] The egg of this form contains a special sort of protoplasm\nnear its vegetative pole, and this part of it is separated at each\nof the first two segmentations by a sort of pseudo-cleavage, leading\nto stages of three and five separated masses instead of two and four,\nthe supernumerary mass being the so-called \u201cyolk-sac\u201d and possessing\nno nuclear elements (Fig. 8). Crampton removed this yolk-sac at the\ntwo-cell stage, and he found that the cleavage of the germs thus\noperated upon was normal except with regard to the size and histological\nappearance of one cell, and that the larvae originating from these\ngerms were complete in every respect except in their mesenchyme, which\nwas wanting. A special part of the protoplasm of the egg had thus been\nbrought into relation with quite a special part of organisation, *and\nthat special part of the protoplasm contained no nucleus*.\n\n[22] *Arch. Entw. Mech.* 3, 1896.\n\n[Illustration: Fig. 8.--The Mollusc Dentalium (*after* E. B. Wilson).\n\n*a.* The egg, consisting of three different kinds of protoplasmatic\nmaterial.\n\n*b.* First cleavage-stage. There are two cells and one \u201cpseudo-cell,\u201d\nthe yolk-sac, which contains no nucleus. This was removed in Crampton\u2019s\nexperiment.]\n\n\nGENERAL RESULTS OF THE FIRST PERIOD OF \u201cENTWICKELUNGSMECHANIK\u201d\n\nThis experiment of Crampton\u2019s, afterwards confirmed by Wilson himself,\nmay be said to have closed the first period of the new science of\nphysiology of form, a period devoted almost exclusively to the problem\nwhether the theory of nuclear division or, in a wider sense, whether the\ntheory of a strict \u201cevolutio\u201d as the basis of organogenesis was true or\nnot.\n\nIt was shown, as we have seen, that the theory of the \u201cqualitatively\nunequal nuclear division\u201d (\u201cqualitativ-ungleiche Kernteilung\u201d in German)\ncertainly was not true, and that there also was no strict \u201cevolutio\u201d\nin protoplasm. Hence Weismann\u2019s theory was clearly disproved. There\ncertainly is a good deal of real \u201cepigenesis\u201d in ontogeny, a good deal\nof \u201cproduction of manifoldness,\u201d not only with regard to visibility but\nin a more profound meaning. But some sort of pre-formation had also\nbeen proved to exist, and this pre-formation, or, if you like, this\nrestricted evolution, was found to be of two different kinds. First an\nintimate organisation of the protoplasm, spoken of as its polarity and\nbilaterality, was discovered, and this had to be postulated for every\nkind of germs, even when it was overshadowed by immediate obligatory\nregulation after disturbances. Besides that there were cases in which\na real specificity of special parts of the germ existed, a relation of\nthese special parts to special organs: but this sort of specification\nalso was shown to belong to the protoplasm.\n\nIt follows from all we have mentioned about the organisation of\nprotoplasm and its bearing on morphogenesis, that the eggs of different\nanimals may behave rather differently, in this respect, and that\nthe eggs indeed may be classified according to the degree of their\norganisation. Though we must leave a detailed discussion of these\ntopics to morphology proper, we yet shall try shortly to summarise\nwhat has been ascertained about them in the different classes of the\nanimal kingdom. A full regulation of the *intimate* structure of\nisolated blastomeres to a new whole, has been proved to exist in the\nhighest degree in the eggs of all echinoderms, medusae, nemertines,\nAmphioxus, fishes, and in one class of the Amphibia (the *Urodela*);\nit is facultative only among the other class of Amphibia, the *Anura*,\nand seems to be only partly developed or to be wanting altogether among\nctenophora, ascidia, annelids, and mollusca. Peculiarities in the\norganisation of *specific parts* of protoplasm have been proved to occur\nin more cases than at first had been assumed; they exist even in the\nechinoderm egg, as experiments of the last few years have shown; even\nhere a sort of specification exists at the vegetative pole of the egg,\nthough it is liable to a certain kind of regulation; the same is true in\nmedusae, nemertines, etc.; but among molluscs, ascidians, and annelids\nno regulation about the specific organisation of the germ in cleavage\nhas been found in any case.\n\nThe differences in the degree of regulability of the intimate germinal\nstructure may easily be reduced to simple differences in the physical\nconsistency of their protoplasm.[23] But all differences in specific\norganisation must remain as they are for the present; it will be one of\nthe aims of the future theory of development to trace these differences\nalso to a common source.\n\n[23] It deserves notice in this connection, that in some cases the\nprotoplasm of parts of a germ has been found to be more regulable in\nthe earliest stages, when it is very fluid, than later, when it is more\nstiff.\n\nThat such an endeavour will probably be not without success, is clear,\nI should think, from the mere fact that differences with regard to\ngerminal specific pre-formation do not agree in any way with the\nsystematic position of the animals exhibiting them; for, strange as it\nwould be if there were two utterly different kinds of morphogenesis, it\nwould be still more strange if there were differences in morphogenesis\nwhich were totally unconnected with systematic relationship: the\nctenophores behaving differently from the medusae, and Amphioxus\ndifferently from ascidians.\n\n\nSOME NEW RESULTS CONCERNING RESTITUTIONS\n\nWe now might close this chapter, which has chiefly dealt with the\ndisproof of a certain sort of ontogenetic theories, and therefore\nhas been almost negative in its character, did it not seem desirable\nto add at least a few words about the later discoveries relating to\nmorphogenetic restorations of the adult. We have learnt that Weismann\ncreated his concept of \u201creserve plasma\u201d to account for what little\nhe knew about \u201crestitutions\u201d: that is, about the restoration of lost\nparts: he only knew regeneration proper in animals and the formation of\nadventitious buds in plants. It is common to both of these phenomena\nthat they take their origin from typically localised points of the body\nin every case; each time they occur a certain well-defined part of the\nbody is charged with the restoration of the lost parts. To explain\nsuch cases Weismann\u2019s hypothesis was quite adequate, at least in a\nlogical sense. But at present, as we shall discuss more fully in another\nchapter, we know of some very widespread forms of restitution, in which\nwhat is to be done for a replacement of the lost is not entrusted to\n*one* typical part of the body in every case, but in which the whole\nof the morphogenetic action to be performed is transferred in its\n*single* parts to the *single* parts of the body which is accomplishing\nrestoration: each of its parts has to take an individual share in the\nprocess of restoration, effecting what is properly called a certain kind\nof \u201cre-differentiation\u201d (\u201cUmdifferenzierung\u201d), and this share varies\naccording to the relative position of the part in each case. Later on\nthese statements will appear in more correct form than at present, and\nthen it will become clear that we are fully entitled to emphasise at the\nend of our criticism of Weismann\u2019s theory, that his hypothesis relating\nto restorations can be no more true than his theory of development\nproper was found to be.\n\nAnd now we shall pass on to our positive work.\n\nWe shall try to sketch the outlines of what might properly be called an\n*analytical theory of morphogenesis*; that is, to explain the sum of our\nknowledge about organic form-production, gained by experiment and by\nlogical analysis, in the form of a real system, in which each part will\nbe, or at least will try to be, in its proper place and in relation with\nevery other part. Our analytical work will give us ample opportunity of\nmentioning many important topics of so-called general physiology also,\nirrespective of morphogenesis as such. But morphogenesis is always to\nbe the centre and starting-point of our analysis. As I myself approach\nthe subject as a zoologist, animal morphogenesis, as before, will be the\nprincipal subject of what is to follow.\n\n\n2. ANALYTICAL THEORY OF MORPHOGENESIS[24]\n\n[24] Compare my *Analytische Theorie der organischen Entwickelung*,\nLeipzig, 1894, and my reviews in *Ergebnisse der Anatomie und\nEntwickelungsgeschichte*, vols. viii. xi. xiv., 1899-1905. A shorter\nreview is given in *Ergebnisse der Physiologie*, vol. v., 1906. The full\nliterature will be found in these reviews.\n\n\u03b1. THE DISTRIBUTION OF MORPHOGENETIC POTENCIES\n\n*Prospective Value and Prospective Potency*\n\nWilhelm Roux did not fail to see that the questions of the locality and\nthe time of all morphogenetic differentiations had to be solved first,\nbefore any problem of causality proper could be attacked. From this\npoint of view he carried out his fundamental experiments.\n\nIt is only in terminology that we differ from his views, if we prefer\nto call our introductory chapter an analysis of the distribution of\nmorphogenetic potencies. The result will be of course rather different\nfrom what Roux expected it would be.\n\nLet us begin by laying down two fundamental concepts. Suppose we have\nhere a definite embryo in a definite state of development, say a\nblastula, or a gastrula, or some sort of larva, then we are entitled\nto study any special element of any special elementary organ of this\ngerm with respect to what is actually to develop out of this very\nelement in the future actual course of this development, whether it be\nundisturbed or disturbed in any way; it is, so to say, the actual, *the\nreal fate* of our element, that we take in account. I have proposed to\ncall this real fate of each embryonic part in this very definite line\nof morphogenesis its *prospective value* (\u201cprospective Bedeutung\u201d in\nGerman). The fundamental question of the first chapter of our analytical\ntheory of development may now be stated as follows: Is the prospective\nvalue of each part of any state of the morphogenetic line constant,\n*i.e.* is it unchangeable, can it be nothing but one; or is it variable,\nmay it change according to different circumstances?\n\nWe first introduce a second concept: the term *prospective potency*\n(\u201cprospective Potenz\u201d in German) of each embryonic element. The term\n\u201cprospective morphogenetic potency\u201d is to signify the *possible\nfate* of each of those elements. With the aid of our two artificial\nconcepts we are now able to formulate our introductory question thus:\nIs the prospective potency of each embryonic part fully given by\nits prospective value in a certain definite case; is it, so to say,\nidentical with it, or does the prospective potency contain more than the\nprospective value of an element in a certain case reveals?\n\nWe know already from our historical sketch that the latter is true: that\nthe actual fate of a part need not be identical with its possible fate,\nat least in many cases; that the potency of the first four blastomeres\nof the egg of the sea-urchin, for instance, has a far wider range than\nis shown by what each of them actually performs in even this ontogeny.\nThere are more morphogenetic possibilities contained in each embryonic\npart than are actually realised in a special morphogenetic case.\n\nAs the most important special morphogenetic case is, of course, the\nso-called \u201cnormal\u201d one, we can also express our formula in terms of\nspecial reference to it: there are more morphogenetic possibilities in\neach part than the observation of the normal development can reveal.\nThus we have at once justified the application of analytical experiment\nto morphogenesis, and have stated its most important results.\n\nAs the introductory experiments about \u201cEntwickelungsmechanik\u201d have shown\nalready that the prospective potency of embryonic parts, at least in\ncertain cases, *can* exceed their prospective value--that, at least in\ncertain cases, it can be different from it--the concept of prospective\npotency at the very beginning of our studies puts itself in the centre\nof analytical interest, leaving to the concept of prospective value the\nsecond place only. For that each embryonic part actually has a certain\nprospective value, a specified actual fate in every single case of\nontogeny, is clear from itself and does not affirm more than the reality\nof morphogenetic cases in general; but that the prospective value of the\nelements may change, that there is a morphogenetic power in them, which\ncontains more than actuality; in other words, that the term \u201cprospective\npotency\u201d has not only a logical but a factual interest: all these points\namount to a statement not only of the most fundamental introductory\nresults but also of the actual *problems* of the physiology of form.\n\nIf at each point of the germ something else *can* be formed than\nactually is formed, why then does there happen in each case just what\nhappens and nothing else? In these words indeed we may state the chief\nproblem of our science, at least after the fundamental relation of\nthe superiority of prospective potency to prospective value has been\ngenerally shown.\n\nWe consequently may shortly formulate our first problem as the question\nof the distribution of the prospective morphogenetic potencies in the\ngerm. Now this general question involves a number of particular ones.\nUp to what stage, if at all, is there an absolutely equal distribution\nof the potencies over all the elements of the germ? When such an equal\ndistribution has ceased to exist at a certain stage, what are then the\nrelations between the parts of different potency? How, on the other\nhand, does a newly arisen, more specialised sort of potency behave with\nregard to the original general potency, and what about the distribution\nof the more restricted potency?\n\nI know very well that all such questions will seem to you a little\nformal, and, so to say, academical at the outset. We shall not fail to\nattach to them very concrete meanings.\n\n*The Potencies of the Blastomeres*\n\nAt first we turn back to our experiments on the egg of the sea-urchin\nas a type of the germ in the very earliest stages. We know already that\neach of the first two, or each of the first four, or three of the first\nfour blastomeres together may produce a whole organism. We may add that\nthe swimming blastula, consisting of about one thousand cells, when cut\nin two quite at random, in a plane coincident with, or at least passing\nnear, its polar axis, may form two fully developed organisms out of its\nhalves.[25] We may formulate this result in the words: the prospective\npotency of the single cells of a blastula of Echinus is the same for\nall of them; their prospective value is as far as possible from being\nconstant.\n\n[25] If the plane of section passes near the equator of the germ, two\nwhole larvae may be formed also, but in the majority of cases the\n\u201canimal\u201d half does not go beyond the blastula. The specific features of\nthe organisation of the protoplasm come into account here. See also page\n65, note 1.\n\nBut we may say even a little more: what actually will happen in each of\nthe blastula cells in any special case of development experimentally\ndetermined depends on the position of that cell in the whole, if the\n\u201cwhole\u201d is put into relation with any fixed system of co-ordinates; or\nmore shortly, \u201cthe prospective value of any blastula cell is a function\nof its position in the whole.\u201d\n\nI know from former experience that this statement wants a few words of\nexplanation. The word \u201cfunction\u201d is employed here in the most general,\nmathematical sense, simply to express that the prospective value,\nthe actual fate of a cell, will change, whenever its position in the\nwhole is different.[26] The \u201cwhole\u201d may be related to any three axes\ndrawn through the normal undisturbed egg, on the hypothesis that there\nexists a primary polarity and bilaterality of the germ; the axes which\ndetermine this sort of symmetry may, of course, conveniently be taken as\nco-ordinates; but that is not necessary.\n\n[26] A change of the position of the cell is of course effected by each\nvariation of the direction of the cut, which is purely a matter of\nchance.\n\n*The Potencies of Elementary Organs in General*\n\nBefore dealing with other very young germs, I think it advisable to\ndescribe first an experiment which is carried out at a later stage of\nour well-known form. This experiment will easily lead to a few new\nconcepts, which we shall want later on, and will serve, on the other\nhand, as a basis of explanation for some results, obtained from the\nyoungest germs of some other animal species, which otherwise would seem\nto be rather irreconcilable with what our Echinus teaches us.\n\nYou know, from the second lecture, what a gastrula of our sea-urchin\nis. If you bisect this gastrula, when it is completely formed, or\nstill better, if you bisect the gastrula of the starfish, either along\nthe axis or at right angles to it, you get complete little organisms\ndeveloped from the parts: the ectoderm is formed in the typical manner\nin the parts, and so is the endoderm; everything is proportionate and\nonly smaller than in the normal case. So we have at once the important\nresults, that, as in the blastula, so in the ectoderm and in the\nendoderm of our Echinus or of the starfish, the prospective potencies\nare the same for every single element: both in the ectoderm and in\nthe endoderm the prospective value of each cell is a \u201cfunction of its\nposition\u201d (Fig. 9).\n\n[Illustration: Fig. 9.--The Starfish, *Asterias*.\n\n*a*^1. Normal gastrula; may be bisected along the main axis or at right\nangles to it (see dotted lines).\n\n*a*^2. Normal larva, \u201c*Bipinnaria*.\u201d\n\n*b*^1. Small but whole gastrula that results by a process of regulation\nfrom the parts of a bisected gastrula.\n\n*b*^2. Small *but whole* \u201c*Bipinnaria*,\u201d developed out of *b*^1.]\n\nBut a further experiment has been made on our gastrula. If at the moment\nwhen the material of the future intestine is most distinctly marked in\nthe blastoderm, but not yet grown into a tube, if at this moment the\nupper half of the larva is separated from the lower by an equatorial\nsection, you will get a complete larva only from that part which bears\nthe \u201cAnlage\u201d of the endoderm, while the other half will proceed in\nmorphogenesis very well but will form only ectodermal organs. By another\nsort of experiment, which we cannot fully explain here, it has been\nshown that the endoderm if isolated is also only able to form such\norgans as are normally derived from it.\n\nAnd so we may summarise both our last results by saying: though\nectoderm and endoderm have their potencies equally distributed amongst\ntheir respective cells, they possess different potencies compared one\nwith the other. And the same relation is found to hold for all cases of\nwhat we call elementary organs: they are \u201cequipotential,\u201d as we may say,\nin themselves, but of different potencies compared with each other.\n\n*Explicit and Implicit Potencies: Primary and Secondary Potencies*\n\nWe shall first give to our concept of \u201cprospective potency\u201d a few words\nof further analytical explanation with the help of our newly obtained\nknowledge.\n\nIt is clear from what we have stated that the prospective potencies of\nthe ectoderm and of the endoderm, and we may add, of every elementary\norgan in relation to every other, differ between themselves and also in\ncomparison with the blastoderm, from which they have originated. But the\ndiversity of the endoderm with respect to the ectoderm is not of the\nsame kind as its diversity in respect to the blastoderm. The potency\nof the endoderm and that of the ectoderm are both specialised in their\ntypical manner, but compared with the potency of the blastoderm they\nmay be said not only to be specialised but also to be *restricted*: the\npotency of the blastoderm embraces the whole, that of the so-called\ngerm-layer embraces only part of the whole; and this species of\nrestriction becomes clearer and clearer the further ontogeny advances:\nat the end of it in the \u201cultimate elementary organs\u201d there is no\nprospective potency whatever.\n\nA few new terms will serve to state a little more accurately what\nhappens. Of course, with regard to all morphogenesis which goes on\n*immediately* from the blastoderm, the potency of the blastoderm is\nrestricted as much as are the potencies of the germ layers. We shall\ncall this sort of immediate potency *explicit*, and then we see at\nonce that, with regard to their explicit potencies, there are only\ndifferences among the prospective potencies of the elementary organs;\nbut with respect to the *implicit* potency of any of these organs, that\nis with respect to their potency as embracing the faculties of all their\nderivations, there are also not only differences but true morphogenetic\nrestrictions lying at the very foundations of all embryology.\n\nBut now those of you who are familiar with morphogenetic facts will\nobject to me, that what we have stated about all sorts of restrictions\nin ontogeny is not true, and you will censure me for having overlooked\nregeneration, adventitious budding, and so on. To some extent the\ncriticism would be right, but I am not going to recant; I shall only\nintroduce another new concept. We are dealing only with *primary*\npotencies in our present considerations, *i.e.* with potencies which\nlie at the root of true embryology, not with those serving to regulate\ndisturbances of the organisation. It is true, we have in some way\ndisturbed the development of our sea-urchin\u2019s egg in order to study\nit; more than that, it would have been impossible to study it at all\nwithout some sort of disturbance, without some sort of operation.\nBut, nevertheless, no potencies of what may properly be called the\n*secondary* or restitutive type have been aroused by our operations;\nnothing happened except on the usual lines of organogenesis. It is\ntrue, some sort of regulation occurred, but that is included among the\nfactors of ontogeny proper.\n\nWe shall afterwards study more fully and from a more general point of\nview this very important feature of \u201cprimary regulation\u201d in its contrast\nto \u201csecondary regulation\u201d phenomena. At present it must be enough to\nsay that in speaking of the restriction of the implicit potencies in\nform-building we refer only to potencies of the primary type, which\ncontain within themselves some properties of a (primary) regulative\ncharacter.\n\n*The Morphogenetic Function of Maturation in the Light of Recent\nDiscoveries*\n\nTurning again to more concrete matters, we shall first try, with the\nknowledge acquired of the potencies of the blastoderm and the so-called\ngerm layers of Echinus, to understand certain rather complicated\nresults which the experimental morphogenetic study of other animal\nforms has taught us. We know from our historical sketch that there are\nsome very important aberrations from the type, to which the Echinus\ngerm belongs,[27] *i.e.* the type with an equal distribution of the\npotencies over all the blastomeres. We know not only that in cases where\na regulation of the intimate structure of the protoplasm fails to occur\na partial development of isolated cells will take place, but that there\nmay even be a typical disposition of typical cells for the formation of\ntypical organs only, without any regulability.\n\n[27] The reader will remember (see page 65, note 1), that even the germ\nof Echinus is not quite equipotential along its main axis, but it is\nequipotential in the strictest sense around this axis. The germs of\ncertain medusae seem to be equipotential in every respect, even in their\ncleavage stages.\n\nLet us first consider the last case, of which the egg of mollusca is a\ngood type: here there is no equal distribution of potencies whatever,\nthe cleavage-cells of this germ are a sort of real \u201cmosaic\u201d with regard\nto their morphogenetic potentialities. Is this difference between the\ngerm of the echinoderms and the molluscs to remain where it is, and\nnot to be elucidated any further? Then there would be rather important\ndifferences among the germs of different animals, at least with regard\nto the degree of the specification of their cleavage cells, or if we\nascribe differences among the blastomeres to the organisation of the\nfertilised egg ready for cleavage, there would be differences in the\nmorphogenetic organisation of the egg-protoplasm: some eggs would be\nmore typically specialised at the very beginning of morphogenesis than\nothers.\n\nIn the first years of the study of \u201cEntwickelungsmechanik\u201d I pointed out\nthat it must never be forgotten that the egg itself is the result of\norganogenesis. If, therefore, there are real mosaic-like specifications\nin some eggs at the beginning of cleavage, or during it, there may\nperhaps have been an *earlier* stage in the individual history of\nthe egg which did not show such specifications of the morphogenetic\nstructure. Two American authors share the merit of having proved\nthis hypothesis. Conklin showed, several years ago, that certain\nintracellular migrations and rearrangements of material do happen in\nthe first stages of ovogenesis in certain cases, but it is to E. B.\nWilson[28] that science owes a proper and definitive elucidation of the\nwhole subject. Wilson\u2019s researches, pursued not only by descriptive\nmethods,[29] but also by means of analytical experiment, led him to the\nhighly important discovery that the eggs of several forms (nemertines,\nmolluscs), which after maturation show the mosaic type of specification\nin their protoplasm to a more or less high degree, fail to show any\nkind of specification in the distribution of their potencies before\nmaturation has occurred. In the mollusc egg a certain degree of\nspecification is shown already before maturation, but nothing to be\ncompared with what happens afterwards; in the egg of nemertines there is\nno specification at all in the unripe egg.\n\n[28] *Journ. Exp. Zool.* 1, 1904.\n\n[29] Great caution must be taken in attributing any specific\nmorphogenetic part to differently coloured or constructed materials,\nwhich may be observed in the egg-protoplasm in certain cases. They may\nplay such a part, but in other cases they certainly do not (see Lyon,\n*Arch. Entw. Mech.* 23, 1907). The final decision always depends on\nexperiment.\n\nMaturation thus becomes a part of ontogeny itself; it is not with\nfertilisation that morphogenesis begins, there is a sort of ontogeny\nanterior to fertilisation.\n\nThese words constitute a summary of Wilson\u2019s researches. Taken together\nwith the general results obtained about the potencies of the blastula\nand the gastrula of Echinus, they reduce what appeared to be differences\nof degree or even of kind in the specification of the egg-protoplasm *to\nmere differences in the time of the beginning of real morphogenesis*.\nWhat occurs in some eggs, as in those of Echinus, at the time of the\ndefinite formation of the germ layers, leading to a specification and\nrestriction of their prospective potencies, may happen very much earlier\nin other eggs. But there exists in *every* sort of egg an *earliest*\nstage, in which all parts of its protoplasm are equal as to their\nprospectivity, and in which there are no potential diversities or\nrestrictions of any kind.\n\nSo much for differences in the *real material* organisation of the germ\nand their bearing on inequipotentialities of the cleavage cells.\n\n*The Intimate Structure of Protoplasm: Further Remarks*\n\nWhere a typical half- or quarter-development from isolated blastomeres\nhappens to occur, we know already that the impossibility of a regulation\nof the *intimate polar-bilateral* structure may account for it. As this\nimpossibility of regulation probably rests on rather simple physical\nconditions[30] it may properly be stated that equal distribution of\npotencies is not wanting but is only overshadowed here. In this respect\nthere exists a logical difference of fundamental importance between\nthose cases of so-called \u201cpartial\u201d or better, \u201cfragmental\u201d development\nof isolated blastomeres in which a certain embryonic organ is wanting\non account of its specific morphogenetic material being absent, and\nthose cases in which the \u201cfragmental\u201d embryo lacks complete \u201chalves\u201d or\n\u201cquarters\u201d with regard to general symmetry on account of the symmetry\nof its intimate structure being irregularly disturbed. This logical\ndifference has not always received the attention which it undoubtedly\ndeserves. Our hypothetical intimate structure in itself is, of course,\nalso a result of factors concerned in ovogenesis. Only in one case do\nwe actually know anything about its origin: Roux has shown that in the\nfrog it is the accidental path of the fertilising spermatozoon in the\negg which, together with the polar axis, normally determines the plane\nof bilateral symmetry; but this symmetry may be overcome and replaced\nby another, if gravity is forced to act in an abnormal manner upon the\nprotoplasm; the latter showing parts of different specific gravity in\nthe eggs of all Amphibia.\n\n[30] It seems that these physical conditions also--besides the real\nspecifications in the organisation of the egg--may be different before\nand after maturation or (in other cases) fertilisation. (See Driesch,\n*Archiv f. Entwickelungsmechanik*, 7, p. 98; and Brachet, *ibid.* 22, p.\n325.)\n\n*The Neutrality of the Concept of \u201cPotency\u201d*\n\nNow we may close our rather long chapter on the distribution of\npotencies in the germ; it has been made long, because it will prove to\nbe very important for further analytical discussion; and its importance,\nin great measure, is due to its freedom from prepossessions. Indeed,\nthe concept of prospective potency does not prejudice anything; we\nhave said, it is true, that limitations of potencies may be due to\nthe presence of specific parts of organisation in some cases; that,\nat least, they may be connected therewith; but we have not determined\nat all what a prospective potency really is, what the term really is\nto signify. It may seem that such a state of things gives an air of\nemptiness to our discussions, that it leaves uncertain what is the most\nimportant. But, I think, our way of argument, which tries to reach the\nproblems of greatest importance by degrees, though it may be slow, could\nhardly be called wrong and misleading.\n\n\n\u03b2. THE \u201cMEANS\u201d OF MORPHOGENESIS\n\nWe now proceed to an analysis of what may properly be called the *means*\nof morphogenesis, the word \u201cmeans\u201d being preferable to the more usual\none \u201cconditions\u201d in this connection, as the latter would not cover the\nwhole field. It is in quite an unpretentious and merely descriptive\nsense that the expression \u201cmeans\u201d should be understood at present; what\nis usually called \u201cconditions\u201d is part of the morphogenetic means in our\nsense.\n\n\u03b2\u2032. *The Internal Elementary Means of Morphogenesis*\n\nWe know that all morphogenesis, typical or atypical, primary or\nsecondary, goes on by one morphogenetic elementary process following the\nother. Now the very foundation of these elementary processes themselves\nlies in the elementary functions of the organism as far as they result\nin the formation of stable visible products. Therefore the elementary\nfunctions of the organism may properly be called the internal \u201cmeans\u201d of\nmorphogenesis.\n\nSecretion and migration are among such functions; the former happening\nby the aid of chemical change or by physical separation, the latter by\nthe aid of changes in surface tension. But hardly anything more concrete\nhas been made out about these or similar points at present.\n\nWe therefore make no claim to offer a complete system of the internal\nelementary means of morphogenesis. We shall only select from the whole\na few topics of remarkable morphogenetic interest, and say a few words\nabout each.\n\nBut, first of all, let us observe that the elementary means of\nmorphogenesis are far from being morphogenesis themselves. The word\n\u201cmeans\u201d itself implies as much. It would be possible to understand each\nof these single acts in morphogenesis as well as anything, and yet to be\nas far from understanding the whole as ever. All means of morphogenesis\nare only to be considered as the most general frame of events within\nwhich morphogenesis occurs.\n\n*Some Remarks on the Importance of Surface Tension in\nMorphogenesis.*--There are a few purely physical phenomena which have\na special importance in organic morphology, all of them connected\nwith capillarity or surface tension. Soap-lather is a very familiar\nthing to all of you: you know that the soap-solution is arranged here\nin very thin planes separated by spaces containing air: it was first\nproved by Berthold[31] that the arrangement of cells in organic tissues\nfollows the same type as does the arrangement of the single bubbles of\na soap-lather, and B\u00fctschli[32] added to this the discovery that the\nminute structure of the protoplasm itself is that of a foam also. Of\ncourse it is not one fluid and one gas which make up the constituents\nof the structure in the organisms, as is the case in the well-known\ninorganic foams, but two fluids, which do not mix with one another. One\ngeneral law holds for all arrangements of this kind: the so-called law\nof least surfaces, expressed by the words that the sum of all surfaces\nexisting is a minimum; and it again is a consequence of this law, if\ndiscussed mathematically, that four lines will always meet in one point\nand three planes in one line. This feature, together with a certain law\nabout the relation of the angles meeting in one line to the size of the\nbubbles, is realised most clearly in many structures of organic tissues,\nand makes it highly probable, at least in some cases, that capillarity\nis at work here. In other cases, as for instance in many plants, a kind\nof outside pressure, the so-called tissue tension, may account for the\narrangement in surfaces *minimae areae*. Cleavage stages are perhaps\nthe very best type in which our physical law is expressed: and here\nit may be said to have quite a simple application whenever all of the\nblastomeres are of the same physical kind, whilst some complications\nappear in germs with a specialised organisation and, therefore,\nwith differences in the protoplasm of their single blastomeres. In\nsuch instances we may say that the physical law holds as far as the\nconditions of the system permit, these conditions ordinarily consisting\nin a sort of non-homogeneity of the surfaces.\n\n[31] *Studien \u00fcber Protoplasmamechanik*, Leipzig, 1886.\n\n[32] *Unters. \u00fcb. mikroskopische Sch\u00e4ume und das Protoplasma*, Leipzig,\n1892.\n\nIt seems, from the researches of Dreyer,[33] that the formation of\norganic skeletons may also be governed by the physically conditioned\narrangement of protoplasmatic or cellular elements, and some phenomena\nof migration and rearrangement among cleavage cells, as described by\nRoux, probably also belong here.\n\n[33] *Jena. Zeitschr.* 26, 1892.\n\nBut let us never forget that the laws of surface tension only give\nus the most general type of an arrangement of elements in all these\ncases, nothing else. A physical law never accounts for the Specific!\nCapillarity gives us not the least clue to it. As the organic substance,\nat least in many cases, is a fluid, it must of course follow the general\nlaws of hydrostatics and hydrodynamics, but life itself is as little\ntouched by its fluid-like or foam-like properties as it is by the fact\nthat living bodies have a certain weight and mass.\n\nAll indeed that has been described may be said to belong, in the\nbroadest meaning of the word, to what is called by Roux \u201ccorrelation of\nmasses,\u201d though this author originally intended to express by this term\nonly some sorts of passive pressure and deformation amongst embryonic\nparts as discovered especially by His.\n\nWe must be cautious in admitting that any organic feature has been\nexplained, even in the most general way, by the action of physical\nforces. What at first seems to be the result of mechanical pressure may\nafterwards be found to be an active process of growth, and what at first\nseems to be a full effect of capillarity among homogeneous elements may\nafterwards be shown to depend on specialised metabolic conditions of the\nsurfaces as its principal cause.[34]\n\n[34] According to Zur Strassen\u2019s results the early embryology of\n*Ascaris* proceeds almost exclusively by cellular surface-changes: the\nmost typical morphogenetic processes are carried out by the aid of this\n\u201cmeans.\u201d As a whole, the embryology of *Ascaris* stands quite apart and\npresents a great number of unsolved problems; unfortunately, the germ of\nthis form has not been accessible to experiment hitherto.\n\nThere are other physical phenomena too, which assist morphogenesis;\nosmotic pressure for instance, which is also well known to operate in\nmany purely physiological processes. But all these processes are only\nmeans of the organism, and can never do more than furnish the general\ntype of events. They do not constitute life; they are *used* by life;\nlet it remain an open question, for the present, how the phenomenon of\n\u201clife\u201d is to be regarded in general.[35]\n\n[35] Rhumbler has recently published a general survey of all attempts to\n\u201cexplain\u201d life, and morphogenesis in particular, in a physico-chemical\nway (\u201cAus dem L\u00fcckengebiet zwischen organismischer und anorganismischer\nNatur,\u201d *Ergeb. Anat. u. Entw.-gesch.* 15, 1906). This *very\npessimistic* survey is the more valuable as it is written by a convinced\n\u201cmechanist.\u201d\n\n*On Growth*.--Among the internal morphogenetical means which are of\na so-called physiological character, that is, which nobody claims to\nunderstand physically at present, there is in the first place *growth*,\nwhich must be regarded as a very essential one.\n\nAnalytically we must carefully discriminate between the increase in the\nsize of the cavities of an organism by a passive extension of their\nsurfaces and the proper growth of the individual cells, which again\nmay be due either to mere extension or to real assimilation. Osmotic\npressure, of course, plays an important part both in the growth of the\nbody-cavities and in simple cellular extension. We repeat the caution\nagainst believing too much to be explained by this phenomenon: it is the\norganism which by the secretion of osmotic substances in the cavities or\nthe protoplasm of the cells prepares the ground for growth even of this\nosmotic sort. The real cellular growth which proceeds on the basis of\nassimilation cannot, of course, be accounted for by osmotic events, not\neven in its most general type.\n\nOntogenetical growth generally sets in, both in animals and in plants,\nafter the chief lines of organisation are laid out; it is only the\nformation of the definite histological structures which usually runs\nparallel to it.\n\n*On Cell-division.*--We have already said a good deal about the\nimportance of cell-division in ontogeny: it accompanies very many of the\nprocesses of organisation in all living beings. But even then, there are\nthe Protozoa, in the morphogenesis of which it does not occur at all,\nand there have also become known many cases of morphogenesis in higher\nanimals, mostly of the type of regulation, in which cellular division\nis almost or wholly wanting. Therefore, cellular division cannot be\nthe true reason of differentiation, but is only a process, which\nthough necessary in some cases, cannot be essential to it. It must be\nconceded, I believe, that the same conclusion can be drawn from all our\nexperiments on very young stages of the germ.\n\nThe investigations of the last few years have made it quite clear that\neven in organisms with a high power of morphogenetic regulation it is\nalways the form of the whole, but not the individual cell, which is\nsubjected to the regulation processes. Starting from certain results\nobtained by T. H. Morgan, I was able to show that in all the small but\nwhole larvae, reared from isolated blastomeres, the size of the cells\nremains normal, only their number being reduced; and Boveri has shown\nmost clearly that it is always the size of the nucleus--more correctly,\nthe mass of the chromatin--which determines how large a cell of a\ncertain histological kind is to be. In this view, the cell appears even\nmore as a sort of material used by the organism as supplied, just as\nworkmen can build the most different buildings with stones of a given\nsize.\n\n\n\u03b2\u2033. *The External Means of Morphogenesis*\n\nWe now know what internal means of morphogenesis are, and so we may\nglance at some of the most important \u201couter means\u201d or \u201cconditions\u201d of\norganisation.\n\nLike the adult, the germ also requires a certain amount of heat, oxygen,\nand, when it grows up in the sea, salinity in the medium. For the germ,\nas for the adult, there exists not only a minimum but also a maximum\nlimit of all the necessary factors of the medium; the same factor which\nat a certain intensity promotes development, disturbs it from a certain\nother intensity upwards.\n\nWithin the limits of this minimum and this maximum of every outside\nagent there generally is an increase in the rate of development\ncorresponding to the increase of intensity of the agent. The\nacceleration of development by heat has been shown to follow the law of\nthe acceleration of chemical processes by a rise of temperature; that\nseems to prove that certain chemical processes go on during the course\nof morphogenesis.\n\nAlmost all that has been investigated of the part played by the external\nconditions of development has little bearing on specific morphogenesis\nproper, and therefore may be left out of account here: we must, however,\nlay great stress on the general fact that there *is* a very close\ndependence of morphogenesis on the outside factors, lest we should be\naccused afterwards of having overlooked it.\n\nOf course all \u201cexternal\u201d means or conditions of morphogenesis can\nactually relate to morphogenetic processes only by becoming in some way\n\u201cinternal,\u201d but we unfortunately have no knowledge whatever how this\nhappens. We at present are only able to ascertain what must necessarily\nbe accomplished in the medium, in order that normal morphogenesis may go\non, and we can only suppose that there exist certain specific internal\ngeneral states, indispensable for organogenesis but inaccessible to\npresent modes of investigation.[36]\n\n[36] Compare the analytical discussions of Klebs, to whom we owe a great\nseries of important discoveries in the field of morphogenetic \u201cmeans\u201d\nin botany. (*Willk\u00fcrliche Entwickelungs\u00e4nderungen bei Pflanzen*, Jena,\n1903; see also *Biol. Centralblatt*, vol. xxiv., 1904, and my reply to\nKlebs, *ibid.* 23, 1903.)\n\n*The Discoveries of Herbst.*--There are but few points in the doctrine\nof the external means or conditions of organogenesis which have a\nmore special bearing on the specification of proper form, and which\ntherefore require to be described here a little more fully. All\nthese researches, which have been carried out almost exclusively by\nHerbst,[37] relate to the effect of the chemical components of sea-water\nupon the development of the sea-urchin. If we select the most important\nof Herbst\u2019s results, we must in the first place say a few words on\nthe part taken by lime or calcium, not only in establishing specific\nfeatures of form, but in rendering individual morphogenesis possible at\nall. Herbst has found that in sea-water which is deprived of calcium the\ncleavage cells and many tissue cells also completely lose contact with\neach other: cleavage goes on quite well, but after each single division\nthe elements are separated; at the end of the process you find the 808\ncells of the germ together at the bottom of the dish, all swimming about\nlike infusoria. There seems to be some influence of the calcium salts\nupon the physical state of the surfaces of the blastomeres.\n\n[37] *Arch. Entw. Mech.* 17, 1904.\n\nIt is not without interest to note that this discovery has an important\nbearing on the technical side of all experiments dealing with the\nisolation of blastomeres. Since the separation of the single cleavage\nelements ceases as soon as the germs are brought back from the mixture\nwithout lime into normal sea-water, it of course is possible to separate\nthem up to any stage which it is desired to study, and to keep them\ntogether afterwards. Thus, if for instance you want to study the\ndevelopment of isolated cells of the eight-cell stage, you will leave\nthe egg in the artificial mixture containing no calcium until the\nthird cleavage, which leads from the four- to the eight-cell stage, is\nfinished. The single eight cells brought back to normal sea-water at\nthis point will give you the eight embryos you want. All researches\nupon the development of isolated blastomeres since the time of Herbst\u2019s\ndiscovery have been carried out by this method, and it would have been\nquite impossible by the old method of shaking to pursue the study into\nsuch minute detail as actually has been done. It may be added that\ncalcium, besides its cell-uniting action, is also of primary importance\nin the formation of the skeleton.\n\nAmong all the other very numerous studies of Herbst we need only mention\nthat potassium is necessary for the typical growth of the intestine,\njust as this element has been found necessary for normal growth in\nplants, and that there must be the ion SO_4, or in other terms,\nsulphur salts present in the water, in order that the germs may acquire\ntheir pigments and their bilateral symmetry. This is indeed a very\nimportant result, though it cannot be said to be properly understood. It\nis a fact that in water without sulphates the larvae of Echinus retain\nthe radial symmetry they have had in the very earliest stages, and may\neven preserve that symmetry on being brought back to normal sea-water if\nthey have spent about twenty-four hours in the artificial mixture.\n\nWe may now leave the subject of Herbst\u2019s attempts to discover the\nmorphogenetic function of the single constituents of normal sea-water,\nand may devote a few words to the other branch of his investigations,\nthose dealing with the morphogenetic effects of substances which are not\npresent in the water of the sea, but have been added to it artificially.\nHere, among many other achievements, Herbst has made the most\nimportant discovery that all salts of lithium effect radical changes\nin development.[38] I cannot describe fully here how the so-called\n\u201clithium larva\u201d originates; let me only mention that its endoderm is\nformed outside instead of inside, that it is far too large, that there\nis a spherical mass between the ectodermal and the endodermal part of\nthe germ, that a radial symmetry is established in place of the normal\nbilateralism, that no skeleton exists, and that the mesenchyme cells\nare placed in a quite abnormal position. All these features, though\nabnormal, are typical of the development in lithium. The larvae present\nno really pathological appearance at all, and, therefore, it may indeed\nbe said that lithium salts are able to change fundamentally the whole\ncourse of morphogenesis. It detracts nothing from the importance of\nthese discoveries that, at present, they stand quite isolated: only with\nlithium salts has Herbst obtained such strange results, and only upon\nthe eggs of echinids, not even upon those of asterids, do lithium salts\nact in this way.\n\n[38] *Zeitschr. wiss. Zool.* 55, 1902; and *Mitt. Neapel.* 11, 1903.\n\n\n\u03b3. THE FORMATIVE CAUSES OR STIMULI\n\n*The Definition of Cause*\n\nWe cannot begin the study of the \u201ccauses\u201d of the differentiation of\nform without a few words of explanation about the terminology which we\nshall apply. Causality is the most disputed of all categories; many\nmodern scientists, particularly in physics, try to avoid the concept of\ncause altogether, and to replace it by mere functional dependence in\nthe mathematical meaning of the term. They claim to express completely\nby an equation all that is discoverable about any sort of phenomena\nconstantly connected.\n\nI cannot convince myself that such a very restricted view is the right\none: it is very cautious, no doubt, but it is incomplete, for we *have*\nthe concept of the acting \u201ccause\u201d in our Ego and are *forced* to search\nfor applications of it in Nature. On the other hand, it does not at all\nescape me that there are many difficulties, or rather ambiguities, in\napplying it.\n\nWe may call the \u201ccause\u201d of any event, the sum total of all the\nconstellations of facts which must be completed in order that the event\nmay occur; it is in this meaning, for instance, that the first principle\nof energetics applies the term in the words *causa aequat effectum*.\nBut, by using the word only in this very general sense, we deprive\nourselves of many conveniences in the further and more particular study\nof Nature. Would it be better to say that the \u201ccause\u201d of any event is\nthe very last change which, after all the constellations necessary for\nits start are accomplished, must still take place in order that the\nevent may actually occur? Let us see what would follow from such a use\nof the word causality. We here have an animal germ in a certain stage,\nsay a larva of Echinus, which is just about to form the intestine; all\nthe internal conditions are fulfilled, and there is also a certain\ntemperature, a certain salinity, and so on, but there is no oxygen in\nthe water: the intestine; of course, will not grow in such a state of\nthings, but it soon will when oxygen is allowed to enter the dish.\nIs, therefore, oxygen the cause of the formation of the intestine of\nechinus? Nobody, I think, would care to say so. By such reasoning,\nindeed, the temperature, or sodium, might be called the \u201ccause\u201d of\nany special process of morphogenesis. It, therefore, seems to be of\nlittle use to give the name of cause to that factor of any necessary\nconstellation of events which accidentally happens to be the last that\nis realised. But what is to be done then?\n\nMight we not say that the cause of any morphogenetic process is that\ntypical property, or quality, or change, on which its specific character\ndepends, on which depends for example, the fact that now it is the\nintestine which appears, while at another time it is the lens of the\neye? We might very well, but we already have our term for this sort\nof cause, which is nothing else than our prospective potency applied\nto that elementary organ from which the new process takes its origin.\nThe prospective potency indeed is the truly immanent cause of every\nspecification affecting single organogenetic processes. But we want\nsomething more than this.\n\nWe may find what we want by considering that each single elementary\nprocess or development not only has its specification, but also has\nits specific and typical place in the whole--its locality. Therefore\nwe shall call the \u201ccause\u201d of a single morphogenetic process, that\noccurrence on which depends its *localisation*, whether its specific\ncharacter also partly depends on this \u201ccause\u201d or not.[39]\n\n[39] In certain cases part of the specific feature of the process in\nquestion may also depend on the \u201ccause\u201d which is localising it, *e.g.*\nin the galls of plants.\n\nThis definition of \u201ccause\u201d in morphology may be artificial; in any\ncase it is clear. And at the same time the concepts of the prospective\npotency and of the \u201cmeans\u201d of organogenesis now acquire a clear and\ndefinite meaning: potency is the real basis of the specific character\nof every act in morphogenesis, and \u201cmeans,\u201d including conditions, are\nthe sum of all external and internal general circumstances which must be\npresent in order that morphogenetic processes may go on, without being\nresponsible for their specificity or localisation.\n\nIt is implied in these definitions of cause and potency, that the former\nalmost always will be of that general type which usually is called a\nstimulus or \u201cAusl\u00f6sung,\u201d to use the untranslatable German word. There is\nno quantitative correspondence between our \u201ccause\u201d and the morphogenetic\neffect.\n\n*Some Instances of Formative and Directive Stimuli*\n\nAgain it is to Herbst that we owe not only a very thorough logical\nanalysis of what he calls \u201cformative and directive stimuli\u201d[40] but also\nsome important discoveries on this subject. We cannot do more here than\nbarely mention some of the most characteristic facts.\n\n[40] Herbst, \u201cUeber die Bedeutung die Reizphysiologie f\u00fcr die kausale\nAuffassung von Vorg\u00e4ngen in der tierischen Ontogenese\u201d (*Biol.\nCentralblatt*, vols. xiv., 1894, and xv., 1895); *Formative Reize in der\ntierischen Ontogenese*, Leipzig, 1901. These important papers must be\nstudied by every one who wishes to become familiar with the subject. The\npresent state of science is reviewed in my articles in the *Ergebnisse\nder Anatomie und Entwickelungsgeschichte*, vols. xi. and xiv., 1902 and\n1905.\n\nAmongst plants it has long been known that the direction of light or of\ngravity may determine where roots or branches or other morphogenetic\nformations are to arise; in hydroids also we know that these factors\nof the medium may be at work[41] as morphogenetic causes, though most\nof the typical architecture of hydroid colonies certainly is due to\ninternal causes, as is also much of the organisation in plants.\n\n[41] Compare the important papers by J. Loeb, *Untersuchungen zur\nphysiologischen Morphologie der Tiere*, W\u00fcrzburg, 1891-2.\n\nLight and gravity are external formative causes; beside that they are\nmerely \u201clocalisers.\u201d But there also are some external formative stimuli,\non which depends not only the place of the effect, but also part of its\nspecification. The galls of plants are the most typical organogenetic\nresults of such stimuli. The potencies of the plant and the specific\nkind of the stimulus equally contribute to their specification; for\nseveral kinds of galls may originate on one sort of leaves.\n\nScarcely any exterior formative stimuli are responsible for animal\norganisation; and one would hardly be wrong in saying that this\nmorphogenetic independence in animals is due to their comparatively\nfar-reaching functional independence of those external agents which\nhave any sort of direction. But many organogenetic relations are known\nto exist between the single parts of animal germs, each of these parts\nbeing in some respect external to every other; and, indeed, it might\nhave been expected already *a priori*, that such formative relations\nbetween the parts of an animal embryo must exist, after all we have\nlearned about the chief lines of early embryology. If differentiation\ndoes not go on after the scheme of Weismann, that is, if it is not\ncarried out by true \u201cevolutio\u201d from within, how could it be effected\nexcept from without? Indeed, every embryonic part may in some respect be\na possible cause for morphogenetic events, which are to occur on every\nother part: it is here that the very roots of epigenesis are to be found.\n\nHeliotropism and geotropism are among the well-known physiological\nfunctions of plants: the roots are seen to bend away from the light and\ntowards the ground; the branches behave just in the opposite way. It now\nhas been supposed by Herbst that such \u201cdirective stimuli\u201d may also be\nat work among the growing or wandering parts of the embryo, that their\ngrowth or their migration may be determined by the typical character of\nother parts, and that real morphogenetic characters can be the result of\nsome such relation; a sort of \u201cchemotropism\u201d or \u201cchemotaxis\u201d may be at\nwork here. Herbst himself has discussed theoretically several cases of\norganogenesis in which the action of directive stimuli is very probable.\nWhat has become actually known by experiment is not very much at\npresent: the mesenchyme cells of Echinus are directed in their migration\nby specified places in the ectoderm, the pigment cells of the yolk-sac\nof the fish fundulus are attracted by its blood vessels, and nerves\nmay be forced to turn into little tubes containing brain substance;\nbut of course only the first two instances have any bearing on typical\nmorphogenesis.\n\nThe first case of an \u201cinternal formative stimulus\u201d in the proper sense,\nthat is, of one embryonic part causing another to appear, was discovered\nby Herbst himself. The arms of the so-called pluteus of the sea-urchin\nare in formative dependence on the skeleton--no skeleton, no arms; so\nmany skeleton primordia,[42] in abnormal cases, so many arms; abnormal\nposition of the skeleton, abnormal position of the arms: these three\nexperimental observations form the proof of this morphogenetic relation.\n\n[42] I use the word \u201cprimordia\u201d for the German \u201cAnlage\u201d; it is better\nthan the word \u201crudiment,\u201d as the latter may also serve to signify\nthe very last stage of a certain formation that is disappearing\n(phylogenetically).\n\nIt may be simple mechanical contact, or it may be some chemical\ninfluence that really constitutes the \u201cstimulus\u201d in this case;\ncertainly, there exists a close and very specific relation of the\nlocalisation of one part of the embryo to another. Things are much the\nsame in another case, which, after having been hypothetically stated\nby Herbst on the basis of pathological data, was proved experimentally\nby Spemann. The lens of the eye of certain Amphibia is formed of their\nskin in response to a formative stimulus proceeding from the so-called\nprimary optic vesicle. If this vesicle fails to touch the skin, no lens\nappears; and, on the other hand, the lens may appear in quite abnormal\nparts of the skin if they come into contact with the optic vesicle after\ntransplantation.\n\nBut formative dependence of parts may also be of different types.\n\nWe owe to Herbst the important discovery that the eyes of crayfishes,\nafter being cut off, will be regenerated in the proper way, if the optic\nganglion is present, but that an antenna will arise in their place\nif this ganglion has also been removed. There must in this case be\nsome unknown influence of the formative kind on which depends, if not\nregeneration itself, at least its special character.\n\nIn other cases there seems to be an influence of the central nervous\nsystem on the regenerative power in general. Amphibia, for instance,\nare said to regenerate neither their legs (Wolff), nor their tail\n(Godlewski), if the nervous communications have been disturbed. But\nin other animals there is no such influence; and in yet others, as\nfor instance, in Planarians, it must seem doubtful at present whether\nthe morphogenetic influence of the nervous system upon processes of\nrestoration is more than indirect; the movements of the animal, which\nbecome very much reduced by the extirpation of the ganglia, being one of\nthe main conditions of a good regeneration.\n\nOf course, all we have said about the importance of special materials\nin the ripe germ, as bearing on specifically localised organisations,\nmight be discussed again in our present chapter, and our intimate\npolar-bilateral structure of germs may also be regarded as embracing\nformative stimuli, at any rate as far as the actual poles of this\nstructure are concerned. This again would bring us to the problem of\nso-called \u201cpolarity\u201d in general, and to the \u201cinversion\u201d of polarity,\nthat is to a phenomenon well known in plants and in many hydroids and\nworms, viz., that morphogenetic processes, especially of the type of\nrestitutions, occur differently, according as their point of origin\nrepresents, so to speak, the positive or the negative, the terminal or\nthe basal end of an axis, but that under certain conditions the reverse\nmay also be the case. But a fuller discussion of these important facts\nwould lead us deeper and deeper into the science of morphogenesis\nproper, without being of much use for our future considerations.\n\nAnd so we may close this section[43] on formative stimuli or \u201ccauses\u201d\nof morphogenesis by shortly adding, more on account of its factual\nthan of its logical interest, that the phenomenon of the determination\nof sex,[44] according to the latest researches, seems to depend on\ncytological events occurring in the very earliest embryonic stages,\nsay even before ontogeny, and not on formative stimuli proper[45]: it\nseems, indeed, as if the sexual products themselves would account for\nthe sex of the individual produced by them, particularly if there were\ndifferences in their chromatin.[46]\n\n[43] A full analysis of the subject would not only have to deal with\nformative stimuli as inaugurating morphogenetic processes, but also with\nthose stimuli which terminate or stop the single acts of morphogenesis.\nBut little is actually known about this topic, and therefore the reader\nmust refer to my other publications. I will only say here, that the end\nof each single morphogenetic act may either be determined at the very\nbeginning or occur as an actual stopping of a process which otherwise\nwould go on for ever and ever; in the first case some terminating\nfactors are included in the very nature of the morphogenetic act itself.\n\n[44] A full account of the present state of the subject will be found in\nMorgan\u2019s *Experimental Zoology*, New York, 1907.\n\n[45] But there certainly exist many formative relations between the real\nsexual organs and the so-called secondary sexual characters. Herbst has\ngiven a full analytical discussion of all that is known on this subject;\nbut the facts are much more complicated than is generally supposed, and\ndo not lend themselves therefore to short description. See also Foges,\n*Pfl\u00fcger\u2019s Arch.* 93, 1902.\n\n[46] It seems that in some cases (*Dinophilus*, certain Arthropods)\nthe sexual products are invariably determined as \u201carrenogennetic\u201d\nor as \u201cthelygennetic\u201d (Wilson, *Journ. Exp. Zool.* ii. and iii.\n1905-6), whilst in others (Amphibia) the state of maturation or\n\u201csuper\u201d-maturation determines the sex of the future organism (R.\nHertwig, *Verh. D. Zool. Ges.* 1905-7).\n\n\n\u03b4. THE MORPHOGENETIC HARMONIES\n\nLet us now turn again to considerations of a more abstract kind: we have\nbecome acquainted with some morphogenetic interactions among the parts\nof a developing embryo; and, indeed, we can be sure that there exist far\nmore of such interactions than we know at present.\n\nBut it is far from being true that the development of each embryonic\npart depends on the existence or development of every other one.\n\nOn the contrary, it is a very important and fundamental feature\nof organogenesis that it occurs in separate lines, that is to\nsay, in lines of processes which may start from a common root, but\nwhich are absolutely independent of one another in their manner of\ndifferentiation. Roux has coined the term \u201cself-differentiation\u201d to\ndenote this phenomenon, and we admit that this term may be conveniently\nused for the purpose, if only it can be kept in mind that its sense is\nalways relative, and that it is also negative. Suppose a part, *A*,\nshows the phenomenon of self-differentiation: this means that the\nfurther development of *A* is not dependent on certain other parts,\n*B*, *C*, and *D*; it does *not* mean at all that *A* has not been\nformatively dependent on some other parts, *E* or *F* at the time of\nits first appearance, nor does it imply that there might not be many\nformative actions among the constituents of *A* itself.\n\nWe indeed are entitled to say that the ectoderm of Echinus shows\n\u201cself-differentiation\u201d with regard to the endoderm; it acquires its\nmouth, for instance, as has been shown by experiment, even in cases\nwhere no intestine is present at all (Fig. 10); but ectoderm and\nendoderm both are formatively dependent on the intimate and the material\norganisation of the blastoderm. It further seems from the most recent\nexperiments that the nerves and the muscles of the vertebrates are\nindependent of each other in their differentiation, but that their fate\nis probably determined by formative processes in the very earliest\nstages of ontogeny.\n\n[Illustration: Fig. 10.--Pluteus-larva of Sphaerechinus.\n\nThe Intestine (i) is developed outside instead of inside (by means of\nraising the temperature); but the mouth (r) is formed in its normal\nplace. S = Skeleton.]\n\nThe phenomenon of self-differentiation, properly understood, now may\nhelp to the discovery of one most general character of all development.\nIf the phenomenon of self-differentiation really occurs in ontogeny\nin its most different aspects, and if, on the other hand, in spite\nof this relative morphogenetic independence of embryonic parts, the\nresulting organism is one whole in organisation and in function, some\nsort of *harmony of constellation*, as it may properly be styled, must\nbe said to be one of the most fundamental characters of all production\nof individual form. In establishing this harmony we do nothing more\nthan describe exactly what happens: the harmony is shown by the fact\nthat there is a whole organism at the end, in spite of the relative\nindependence of the single events leading to it.\n\nBut still another sort of harmony is revealed in morphogenesis, by an\nanalysis of the general conditions of the formative actions themselves.\nIn order that these actions may go on properly the possibility must be\nguaranteed that the formative causes may always find something upon\nwhich to act, and that those parts which contain the potencies for the\nnext ontogenetic stage may properly receive the stimuli awaking these\npotencies: otherwise there would be no typical production of form at\nall. This, the second species of harmonious relations to be described in\nontogeny, may be called *causal harmony*; the term simply expresses the\nunfailing relative condition of formative causes and cause-recipients.\n\nFinally, in *functional harmony* we have an expression descriptive\nof the unity of organic function, and so we may state, as the latest\nresult of our analytical theory of development up to this point, that\nindividual morphogenesis is marked by a *threefold harmony* among its\nparts.\n\n\n\u03b5. ON RESTITUTIONS[47]\n\n[47] Driesch, *Die organischen Regulationen*, Leipzig, 1901; Morgan,\n*Regeneration*, New York, 1901.\n\nAt this stage we leave for a while our analytical studies of ontogeny\nproper. We must not forget that typical ontogenesis is not the only form\nin which morphogenesis can occur: the organic form is able to restore\ndisturbances of its organisation, and it certainly is to be regarded as\none of the chief problems of analytical morphogenesis to discover the\nspecific and real stimulus which calls forth the restoring processes.\nFor simply to say that the disturbance is the cause of the restoration\nwould be to evade the problem instead of attacking it. But there are\nstill some other problems peculiar to the doctrine of restitutions.\n\n*A few Remarks on Secondary Potencies and on Secondary Morphogenetic\nRegulations in General*\n\nWe have only briefly mentioned in a previous chapter that there\nexist many kinds of potencies of what we call the secondary or truly\nrestitutive type, and that their distribution may be most various and\nquite independent of all the potencies for the primary processes\nof ontogeny proper. Let us first add a few words about the concept\nof \u201csecondary restitution\u201d and about the distribution of secondary\npotencies in general.\n\nPrimary ontogenetic processes founded upon primary potencies may *imply*\nregulation, or more correctly, restitution in many cases: so it is,\nwhen fragments of the blastula form the whole organism, or when the\nmesenchyme cells of Echinus reach their normal final position by an\nattraction on the part of specific localities of the ectoderm in spite\nof a very abnormal original position enforced upon them by experiment.\nIn these cases we speak of primary regulations or restitutions;\ndisturbances are neutralised by the very nature of the process in\nquestion. We speak of secondary restitution whenever a disturbance\nof organisation is rectified by processes foreign to the realm of\nnormality; and these abnormal lines of events are revealed to us in the\nfirst place by the activity of potencies which remain latent in ontogeny\nproper.\n\nWe know already that a certain kind of secondary restitution has\nbeen discovered lately, very contradictory to the theoretical views\nof Weismann; the process of restoration being carried out not by any\ndefinite part of the disturbed organisation, but by all the single\nelements of it. The problem of the distribution of secondary potencies\nin these cases of so-called \u201cre-differentiation\u201d is to form our special\nstudy in the next chapter. In all other cases restoration processes\nstart from specific localities; if they occur on the site of the\nwound which caused the disturbance, we speak of regeneration; if they\noccur at some distance from the wound, we call them adventitious\nprocesses. Besides these three types of processes of restitution there\nmay be mentioned a fourth one, consisting in what is generally called\ncompensatory hypertrophy; the most simple case of such a compensatory\nprocess is when one of a pair of organs, say a kidney, becomes larger\nafter the other has been removed.[48] Finally, at least in plants, a\nchange of the directive irritability, of so-called \u201cgeotropism\u201d for\ninstance, in certain parts may serve to restore other more important\nparts.\n\n[48] But real compensatory differentiation occurs in the cases of\nso-called \u201chypertypy\u201d as first discovered by Przibram and afterwards\nstudied by Zeleny: here the two organs of a pair show a different degree\nof differentiation. Whenever the more specialised organ is removed the\nless developed one assumes its form. Similar cases, which might simply\nbe called \u201ccompensatory heterotypy,\u201d are known in plants, though only\nrelating to the actual fate of undifferentiated \u201cAnlagen\u201d in these\norganisms. A leaf may be formed out of the Anlage of a scale, if all the\nleaves are cut off, and so on.\n\nIn two of these general types of restitution, in regeneration proper and\nin the production of adventitious organs, the potencies which underlie\nthese processes may be said to be \u201ccomplex.\u201d It is a complicated series\nof events, a proper morphogenesis in itself, for which the potency\nhas to account, if, for instance, a worm newly forms its head by\nregeneration, or if a plant restores a whole branch in the form of an\nadventitious bud.\n\nSuch generalisations as are possible about the distribution of complex\npotencies are reserved for a special part of our future discussion.\n\nSecondary restitution is always, like ontogeny, a process of\nmorphogenesis, and therefore all the questions about single formative\nstimuli, and about internal and external conditions or means, occur\nagain. But of course we cannot enter into these problems a second time,\nand may only say that, especially in regeneration proper, the specific\ntype of the regenerative formation of any part may differ very much from\nthe ontogenetic type of its origin: the end of both is the same, but the\nway can be even fundamentally different in every respect.\n\n*The Stimuli of Restitutions*[49]\n\n[49] For a fuller analysis compare my opening address delivered before\nthe section of \u201cExperimental Zoology\u201d at the Seventh Zoological\nCongress, Boston, 1907: \u201cThe Stimuli of Restitutions\u201d (see Proceedings\nof that Congress).\n\nBut now we turn to the important question: what is the precise\nstimulus[50] that calls forth processes of restitution; or, in other\nwords, what must have happened in order that restitution may occur?\n\n[50] The problem of the stimulus of a secondary restitution as a\nwhole must not be confused with the very different question, what the\nsingle \u201cformative stimuli\u201d concerned in the performance of a certain\nrestitutive act may be. With regard to restitution as a *whole* these\nsingle \u201cformative stimuli\u201d might properly be said to belong to its\n\u201cinternal means\u201d--in the widest sense of the word.\n\nThat the operation in itself, by its removing of mechanical obstacles,\ncannot be the true stimulus of any restitutions, is simply shown by all\nthose restitutions that do not happen at the place of the wound. If we\ntook a narrower point of view, and if we only considered regeneration\nproper from the wound itself, we might probably at first be inclined to\nadvocate the doctrine that the removing of some obstacles might in fact\nbe the stimulus to the process of restoration; but, even then, why is\nit that just what is wanted grows out? Why is there not only growth,\nbut specific growth, growth followed by specification? The removing\nof an obstacle could hardly account for that. But, of course, taking\naccount of all the adventitious restitutions--that is, all restorations\nnot beginning at the wound itself--the theory that the removing of\nobstacles is the stimulus to restoration becomes, as we have said, quite\nimpossible.[51]\n\n[51] T. H. Morgan is very right in stating that, in regeneration, the\n\u201cobstacle\u201d itself is newly formed by the mere process of healing,\nprevious to all restitution, and that true restitution happens all the\nsame.\n\nBut where then is the stimulus to be found? There is another rather\nsimple theory of the \u201cAusl\u00f6sung\u201d of restitutions,[52] which starts\nfrom the phenomena of compensatory hypertrophy and some occurrences\namong plants. The removal of some parts of the organism, it is said,\nwill bring its other parts into better conditions of nutrition, and\ntherefore these parts, particularly if they are of the same kind, will\nbecome larger. Granted for the moment that such a view may hold in cases\nwhen one of a pair of glands becomes larger after the other has been\nremoved, or when pruning of almost all the leaves of a tree leads to the\nrest becoming larger, it certainly must fail to explain the fact that\nin other cases true *new* formations may arise in order to restore a\ndamaged part, or that the latter may be regenerated in its proper way.\nFor *merely quantitative* differences in the mixture of the blood or of\nthe nourishing sap in plants can never be a sufficient reason for the\nhighly typical and *qualitative* structure of newly-formed restitutions.\nAnd even in the most simple cases of a mere increase in the size of\nsome parts, that is, in the simplest cases of so-called compensatory\nhypertrophy,[53] it is at least doubtful, if not very improbable, that\nthe compensation is accomplished in such a purely passive way, because\nwe know that in other cases it is usually the growth of the young parts\nthat actively attracts the nourishment: there is first differentiation\nand growth, and *afterwards* there is a change in the direction of the\nnourishing fluids.\n\n[52] I merely mention here the still \u201csimpler\u201d one--applicable of course\nto regeneration proper exclusively--that for the simple reason of being\n\u201cwounded,\u201d *i.e.* being a surface open to the medium, the \u201cwound\u201d brings\nforth all that is necessary to complete the organism.\n\n[53] That compensatory hypertrophy cannot be due to \u201cfunctional\nadaptation\u201d--to be analysed later on--was proved by an experiment of\nRibbert\u2019s. Compensation may occur before the function has made its\nappearance, as was shown to be the case in the testicles and mammae of\nrabbits. (*Arch. Entw. Mech.* 1, 1894, p. 69.)\n\nThe process of true regeneration, beginning at the locality of the wound\nitself, has been shown by Morgan, even as regards its rate, to occur\nquite irrespectively of the animal being fed or not.[54] There could\nhardly be a better demonstration of the fundamental fact that food\nassists restitution, but does not \u201ccause\u201d it in any way.\n\n[54] At any given time only the absolute size of the regenerated part is\ngreater in animals which are well fed; the degree of differentiation is\nthe same in all. Zeleny has found that, if all five arms of a starfish\nare removed, each one of them will regenerate more material in a given\ntime than it would have done if it alone had been removed. But these\ndifferences also only relate to absolute size and not to the degree\nof differentiation. They possibly may be due in fact to conditions of\nnourishment, but even here other explanations seems possible (Zeleny,\n*Journ. exp. Zool.* 2, 1905).\n\nBut in spite of all we have said, there seems to be some truth in\nregarding the nutritive juices of animals and plants as somehow\nconnected with the stimulus of restitutions: only in this very cautious\nform, however, may we make the hypothesis. It has been shown for both\nanimals and plants, that morphogenesis of the restitutive type may be\ncalled forth even if the parts, now to be \u201cregenerated\u201d have not been\nactually removed; *e.g.* in the so-called super-regeneration of legs\nand tails in Amphibia, of the head in Planarians, of the root-tip in\nplants and in some other cases. Here it has always been a disturbance\nof the normal connection of some parts with the rest of the organism\nwhich proved to be the reason of the new formation. This shows that\nsomething to do with the communication among parts is at least connected\nwith restitution, and this communication may go on either by the unknown\naction of specific tissues or by the aid of the blood or sap.[55] But\nin what this change or break of specific communication consists, is\nabsolutely unknown. One might suppose that each part of the organisation\nconstantly adds some sort of ferment to the body fluids outside or\ninside the cells, that the removing of any part will change the\ncomposition of these fluids in this particular respect, and that this\nchange acts as a sort of communication to summon the restituting parts\nof the whole to do their duty.[56]\n\n[55] For a good discussion of \u201csuper-regeneration\u201d in the roots of\nplants see N\u011bmec, *Studien \u00fcber die Regeneration*, Berlin, 1905. Goebel\nand Winkler have succeeded in provoking the \u201crestitution\u201d of parts which\nwere not removed at all by simply stopping their functions (leaves of\ncertain plants were covered with plaster, etc.). (*Biol. Centralbl.* 22,\n1902, p. 385; *Ber. Bot. Ges.* 20, 1902, p. 81.) A fine experiment is\ndue to Miehe. The alga *Cladophora* was subjected to \u201cplasmolysis,\u201d each\ncell then formed a new membrane of its own around the smaller volume of\nits protoplasm; after that the plants were brought back to a medium of\nnormal osmotic pressure, and then each single cell grew up into a little\nplant (all of them being of the same polarity!). Two questions seem\nto be answered by this fact: loss of communication is of fundamental\nimportance to restitution, and the removal of mechanical obstacles plays\nno part in it, for the mechanical resistances were the same at the end\nof the experiment as they had been at the beginning. (*Ber. Bot. Ges.*\n23, 1905, p. 257.) For fuller analysis of all the problems of this\nchapter see my Organische Regulationen, my reviews in the *Ergebnisse\nder Anatomie und Entwickelungsgeschichte*, vols. viii. xi. xiv., and\nmy Boston address mentioned above. Compare also Fitting, *Ergebn. d.\nPhysiol.* vols. iv. and v.\n\n[56] The so-called \u201cinner secretion\u201d in physiology proper would offer a\ncertain analogy to the facts assumed by such an hypothesis. Compare the\nexcellent summary given by E. Starling at the seventy-eighth meeting of\nthe German \u201cNaturforscherversammlung,\u201d Stuttgart, 1906.\n\nBut I see quite well that such a theory is very little satisfactory;\nfor what has to be done in restitution in each case is not a simple\nhomogeneous act, for which one special material might account, but is\na very complicated work in itself. It was the defect of the theory of\n\u201corgan-forming substances\u201d as advocated by Sachs, that it overlooked\nthis point.\n\nSo all we know about the proper stimuli of restitutions is far from\nresting on any valid grounds at all; let us not forget that we are\nhere on the uncertain ground of what may be called the newest and\nmost up-to-date branch of the physiology of form. No doubt, there\nwill be something discovered some day, and the idea of the \u201cwhole\u201d in\norganisation will probably play some part in it. But in what manner that\nwill happen we are quite unable to predict.\n\nThis is the first time that, hypothetically at least, the idea of the\nwhole has entered into our discussion. The same idea may be said to\nhave entered it already in a more implicit form in the statement of the\nthreefold harmony in ontogeny.\n\nLet us now see whether we can find the same problem of the \u201cwhole\u201d\nelsewhere, and perhaps in more explicit and less hypothetical form.\nLet us see whether our analytical theory of development is in fact as\ncomplete as it seemed to be, whether there are no gaps left in it which\nwill have to be filled up.\n\n\n3. THE PROBLEM OF MORPHOGENETIC LOCALISATION\n\n\u03b1. THE THEORY OF THE HARMONIOUS-EQUIPOTENTIAL SYSTEM\n\nFIRST PROOF OF THE AUTONOMY OF LIFE\n\nWe have come to the central point of the first part of these lectures;\nwe shall try in this chapter to decide a question which is to give life\nits place in Nature, and biology its place in the system of sciences.\nOne of the foundation stones is to be laid upon which our future\nphilosophy of the organism will rest.\n\n\n*The General Problem*\n\nOur analytical theory of morphogenesis has been founded upon three\nelementary concepts: the prospective potency, the means, and the\nformative stimulus. Its principal object has been to show that all\nmorphogenesis may be resolved into the three phenomena expressed by\nthose concepts; in other terms, that morphogenesis may be proved to\nconsist simply and solely of what is expressed by them. Have we indeed\nsucceeded in attaining this object? Has nothing been left out? Is it\nreally possible to explain every morphogenetic event, at least in the\nmost general way, by the aid of the terms potency, means, and stimulus?\n\nAll of these questions are apt to lead us to further considerations.\nPerhaps these considerations will give us a very clear and simple result\nby convincing us that it is indeed possible to analyse morphogenesis in\nour schematic way.\n\nBut if the answer were a negative one? What would that suggest?\n\nThe full analysis of morphogenesis into a series of single formative\noccurrences, brought about by the use of given means and on the basis of\ngiven potencies, might assure us, perhaps, that, though not yet, still\nat some future time, a further sort of analysis will be possible: the\nanalysis into the elemental facts studied by the sciences of inorganic\nnature. The organism might prove to be a machine, not only in its\nfunctions but also in its very origin.\n\nBut what are we to say if even the preliminary analysis, which possibly\nmight lead to such an ultimate result, fails?\n\nLet us then set to work. Let us try to consider most carefully the topic\nin which our concept of the formative cause or stimulus may be said\nto be centred, the *localisation* of all morphogenetic effects. Is it\nalways possible in fact to account for the typical localisation of every\nmorphogenetic effect by the discovery of a single specific formative\nstimulus? You will answer me, that such an analysis certainly is not\npossible at present. But I ask you again, are there any criteria that it\nis possible, at least in principle; or are there any criteria which will\nrender such an aim of science impossible for all future time?\n\n\n*The Morphogenetic \u201cSystem\u201d*\n\nWe know from our experimental work that many, if not all, of the\nelementary organs in ontogeny show one and the same prospective\npotency distributed equally over their elements. If we now borrow a\nvery convenient term from mechanics, and call any part of the organism\nwhich is considered as a unit from any morphogenetic point of view, a\nmorphogenetic \u201c*system*,\u201d we may sum up what we have learnt by saying\nthat both the blastoderm of the echinoderms, at least around its\npolar axis, and also the germ-layers of these animals, are \u201csystems\u201d\npossessing an equal potentiality in all of their elements, or, in short,\nthat they are *equipotential systems*.\n\nBut such a term would not altogether indicate the real character of\nthese systems.\n\nLater on we shall analyse more carefully than before the distribution\nof potencies which are the foundation both of regeneration proper and\nof adventitious growth, and then we shall see that, in higher plants\nfor instance, there is a certain \u201csystem\u201d which may be called the\norgan proper of restitutions, and which also in each of its elements\npossesses the same restoring potency; I refer to the well-known cambium.\nThis cambium, therefore, also deserves the name of an \u201cequipotential\nsystem.\u201d But we know already that its potencies are of the complex\ntype, that they consist in the faculty of producing the *whole*, of\nsuch a complicated organisation as a branch or a root, that the term\n\u201cequipotential system\u201d is here only to signify that such a complicated\nunit may arise out of each of the cells of the cambium.\n\nThe potencies we have been studying in the blastula or gastrula of\nechinoderms are not of the complex type: our systems are equipotential\nto the extent that each of their elements may play every *single* part\nin the totality of what will occur in the whole system; it is to\nthis *single* part that the term \u201cfunction of the position\u201d relates.\nWe therefore might call our systems equipotential systems with single\npotencies; or, more shortly, singular-equipotential systems.\n\nBut even this terminology would fail to touch precisely the very\ncentre of facts: it is not only the simplicity or singularity of\ntheir potencies which characterises the r\u00f4le of our systems in\nmorphogenesis,[57] but far more important with respect to the production\nof form are two other leading results of the experimental researches.\nThe proper act to be performed by every element in each actual case is\nin fact a single one, but the potency of any element as such consists\nin the possibility of many, nay of indefinitely many, single acts:\nthat then might justify us in speaking of our systems as \u201cindefinite\nequipotential,\u201d were it not that another reason makes another title seem\nstill more preferable. There are indeed indefinite singular potencies at\nwork in all of our systems during ontogeny: but the sum of what happens\nto arise in every case out of the sum of the single acts performed by\nall of the single equipotential cells is not merely a sum but a unit;\nthat is to say, there exists a sort of harmony in every case among the\n*real products* of our systems. The term *harmonious-equipotential\nsystem* therefore seems to be the right one to denote them.\n\n[57] The name of singular-equipotential systems might also be applied\nto elementary organs, the single potencies of which are awaked to\norganogenesis by specific formative stimuli from without; but that is\nnot the case in the systems studied in this chapter.\n\nWe now shall try first to analyse to its very extremes the meaning of\nthe statement that a morphogenetic system is harmonious-equipotential.\n\n\n*The \u201cHarmonious-Equipotential System\u201d*\n\nWe have an ectoderm of the gastrula of a starfish here before us; we\nknow that we may cut off any part of it in any direction, and that\nnevertheless the differentiation of the ectoderm may go on perfectly\nwell and result in a typical little embryo, which is only smaller in\nits size than it would normally be. It is by studying the formation of\nthe highly complicated ciliary band, that these phenomena can be most\nclearly understood.\n\nNow let us imagine our ectoderm to be a cylinder instead of being\napproximately a sphere, and let us imagine the surface of this cylinder\nunrolled. It will give us a plane of two definite dimensions, *a* and\n*b*. And now we have all the means necessary for the analytical study of\nthe differentiation of an harmonious-equipotential system.\n\nOur plane of the dimensions *a* and *b* is the basis of the normal,\nundisturbed development; taking the sides of the plane as fixed\nlocalities for orientation, we can say that the actual fate, the\n\u201cprospective value\u201d of every element of the plane stands in a fixed and\ndefinite correlation to the length of two lines, drawn at right angles\nto the bordering lines of the plane; or, to speak analytically, there\nis a definite actual fate corresponding to each possible value of *x*\nand of *y*. Now, we have been able to state by our experimental work,\nthat the prospective value of the elements of our embryonic organ is not\nidentical with their \u201cprospective potency,\u201d or their possible fate, this\npotency being very much richer in content than is shown by a single case\nof ontogeny. What will be the analytical expression of such a relation?\n\nLet us put the question in the following way: on what factors does\nthe fate of any element of our system depend in all possible cases\nof development obtainable by means of operations? We may express our\nresults in the form of an equation:--\n\n    *p.v. (X) = f( ... )*\n\n*i.e.* \u201cthe prospective value of the element *X* is a function of\n...\u201d--of what?\n\nWe know that we may take off any part of the whole, as to quantity, and\nthat a proportionate embryo will result, unless the part removed is of\na very large size. This means that the prospective value of any element\ncertainly depends on, certainly is a function of, the *absolute size*\nof the actually existing part of our system in the particular case. Let\n*s* be the absolute size of the system in any actual experimental case\nof morphogenesis: then we may write *p.v. (X) = f(s ... )*. But we\nshall have to add still some other letter to this *s*.\n\nThe operation of section was without restriction either as to the\namount of the material removed from the germ, or as to the direction of\nthe cut. Of course, in almost every actual case there will be both a\ndefinite size of the actual system and a definite direction of the cut\ngoing hand-in-hand. But in order to study independently the importance\nof the variable direction alone, let us imagine that we have isolated\nat one time that part of our system which is bounded by the lines *a_1\nb_1*, and at another time an equal amount of it which has the lines\n*a_2 b_2* as its boundaries. Now since in both cases a typical small\norganism may result on development, we see that, in spite of their equal\nsize the prospective value of every element of the two pieces cut\nout of the germ may vary even in relation to the direction of the cut\nitself. Our element, *X*, may belong to both of these pieces of the same\nsize: its actual fate nevertheless will be different. Analytically, it\nmay be said to change in correspondence to the actual position of the\nactual boundary lines of the piece itself with regard to the fundamental\nlines of orientation, *a* and *b*; let this actual position be expressed\nby the letter *l*, *l* marking the distance of one[58] of the actual\nboundary lines of our piece from *a* or *b*: then we are entitled to\nimprove our formula by writing *p.v. (X) = f(s, l ... )* (Fig.\n11).\n\n[58] The distance of the other boundary line from *a* or *b* would be\ngiven by the value of *s*.\n\n[Illustration: Fig. 11.--Diagram to show the Characteristics of an\n\u201cHarmonious-equipotential System.\u201d\n\nThe element *X* forms part of the systems *a b* or *a_1 b_1* or\n*a_2 b_2*; its prospective value is different in each case.]\n\nBut the formula is not yet complete: *s* and *l* are what the\nmathematicians call variables: they may have any actual value and there\nwill always be a definite value of *p.v.*, *i.e.* of the actual fate\nwhich is being considered; to every value of *s* and *l*, which as\nwe know are independent of each other, there corresponds a definite\nvalue of the actual prospectivity. Now, of course, there is also a\ncertain factor at work in every actual case of experimental or normal\ndevelopment, which is *not* a variable, but which is the same in all\ncases. This factor is a something embraced in the prospective potency\nof our system, though not properly identical with it.\n\nThe prospective potency of our system, that is to say of each of its\nelements, is the sum total of what can be done by all; but the fact\nthat a typically proportionate development occurs in every possible\ncase, proves that this sum comes into account, not merely as a sum,\nbut as a sort of order: we may call this order the \u201crelation of\nlocalities in the absolutely normal case.\u201d If we keep in mind that the\nterm \u201cprospective potency\u201d is always to contain this order, or, as we\nmay also call it, this \u201crelative proportionality,\u201d which, indeed, was\nthe reason for calling our systems \u201charmonious,\u201d then we may apply it\nwithout further explanation in order to signify the *non-variable*\nfactor on which the prospective value of any element of our systems\ndepends, and, if we denote the prospective potency, embracing order,\nby the letter *E*, we are now able to complete our formula by saying\n*p.v. (X) = f(s, l, E)*. So far the merely analytical study of the\ndifferentiation of harmonious-equipotential systems.[59]\n\n[59] A far more thorough analysis of this differentiation has been\nattempted in my paper, \u201cDie Localisation morphogenetischer Vorg\u00e4nge. Ein\nBeweis vitalistischen Geschehens,\u201d Leipzig, 1899.\n\n\n*Instances of \u201cHarmonious-Equipotential Systems\u201d*\n\nWe must try at first to learn a few more positive facts about our\nsystems, in order that we may know how important is the part which they\nplay in the whole animal kingdom, and in order that our rather abstract\nanalysis may become a little more familiar to us. We know already that\nmany of the elementary morphogenetic organs have been really proved to\nbe harmonious-equipotential systems, and that the same probably is true\nof many others; we also know that the immature egg of almost all animals\nbelongs to this type, even if a fixed determination of its parts may\nbe established just after maturation. Moreover, we said, when speaking\nabout some new discoveries on form-restitution, that there are many\ncases in which the processes of restitution do not proceed from single\nlocalities, the seat of complex potencies in the organism, but in which\neach *single* part of the truncated organism left by the operation has\nto perform one *single* act of restoration, the full restitution being\nthe result of the totality of all. These cases must now be submitted to\na full analysis.\n\nAll of you have seen common sea-anemones or sea-roses, and many of you\nwill also be familiar with the so-called hydroid polyps. *Tubularia*\nis one genus of them: it looks like a sea-anemone in miniature placed\non the top of a stem like a flower. It was known already to Allman\nthat *Tubularia* is able to restore its flower-like head when that\nis lost, but this process was taken to be an ordinary regeneration,\nuntil an American zoologist, Miss Bickford, succeeded in showing that\nthere was no regeneration process at all, in the proper sense of the\nword, no budding of the missing part from the wound, but that the new\ntubularian head was restored by the combined work of many parts of the\nstem. Further analysis then taught us that *Tubularia* indeed is to be\nregarded as the perfect type of an harmonious-equipotential system: you\nmay cut the stem at whatever level you like: a certain length of the\nstem will always restore the new head by the co-operation of its parts.\nAs the point of section is of course absolutely at our choice, it is\nclear, without any further discussion, that the prospective value of\neach part of the restoring stem is a \u201cfunction of its position,\u201d that\nit varies with its distance from the end of the stem; and so at once\nwe discover one of the chief characteristics of our systems. But also\nthe second point which enters into our formula can be demonstrated in\n*Tubularia*: the dependence of the fate of every element on the actual\nsize of the system. You would not be able to demonstrate this on very\nlong stems, but if you cut out of a *Tubularia* stem pieces which are\nless than ten millimetres in length, you will find the absolute size\nof the head restored to be in close relation to the length of the stem\npiece, and this dependence, of course, includes the second sort of\ndependence expressed in our formula.\n\nThe figures will serve to show you a little more concretely what has\nbeen described. The head of *Tubularia* consists of a sort of broad base\nwith a thin proboscis upon it, both bearing a large number of tentacles;\nthese tentacles are the first things to be seen as primordia (\u201cAnlagen\u201d)\nin the process of restitution. You notice two rings of longitudinal\nlines inside the stem; the lines will become walls and then will\nseparate from the stem until they are only connected with it at their\nbasal ends; the new tentacles are ready as soon as that has happened,\nand a process of growth at the end will serve to drive the new head out\nof the so-called perisarc or horny skeleton, which surrounds the stem.\nBy comparing the two figures, 12 *e*, and *g*, you easily find out that\nthe absolute lengths of the two tentacle rings are very different, and\nthat both are in proportion[60] to the actual size of the stem (Fig. 12).\n\n[60] This statement is *not strictly* correct for *Tubularia*. I found\n(*Archiv f. Entwickelungsmechanik*, ix. 1899), that a reduction of the\nlength of the stem is always followed by a reduction of the size of the\nhydranth-primordium, but there is no real proportionality between them.\nIt is only for theoretical simplification that a strict proportionality\nis assumed here, both in the text and the diagram. But there is an\nalmost strict proportionality in all cases of \u201cclosed forms.\u201d\n\n[Illustration: Fig. 12.--Tubularia.\n\n*a.* Diagram of the \u201cHydranth,\u201d with its short and long tentacles.\n\n*b.* Restitution of a new hydranth inside the perisarc (*p*).\n\n*c.* The same--later stage; the tentacles are complete; the whole\nhydranth will be driven out of the perisarc by a process of growth that\noccurs at the locality marked \u2b06.\n\n*d.* A stem of *Tubularia* cut either at *a_1 b_1* or at *a_2 b_2*,\nor at *a_1 c*.\n\n*e.* Position of tentacles in the piece cut at *a_1 b_1*.\n\n*f.* Position of tentacles in the piece cut at *a_2 b_2*,\nwhich is equal in length to *a_1 b_1*.\n\n*g.* Position of tentacles in the piece cut at *a_1 c*,\nwhich is half as long as *a_1 b_1*.]\n\nSo we find our formula *p.v. (X) = f(s, l, E)* very well\nillustrated in *Tubularia*. The formula indeed may help us to predict,\nin any case, where a certain part of the polyp\u2019s organisation is\nto originate, at least if we know all that is included under our\nletter *E*, *i.e.* the normal proportion of our form. Of course such\nprediction would not have much practical importance in all our cases of\nmorphogenesis, but nevertheless I should like to state here that it is\npossible; for many scientific authors of recent times have urged the\nopinion that prediction of, and domination over, what will happen, can\nbe the only true aims of sciences at all. I myself judge these aims to\nbe of second or third-rate importance only, but, if they may be reached\nby what our purely theoretical study teaches, so much the better.\n\nAnother very typical case of a morphogenetic system of the harmonious\ntype is supplied by the phenomena of restoration in the ascidian\n*Clavellina*. I cannot fully describe the organisation of this form\n(Fig. 13a), and it must suffice to say that it is very complicated,\nconsisting of two very different chief parts, the branchial apparatus\nand the so-called intestinal sac; if these two parts of the body of\n*Clavellina* are separated one from the other, each may regenerate the\nother in the typical way, by budding processes from the wound. But, as\nto the branchial apparatus, there may happen something very different:\nit may lose almost all of its organisation and become a small white\nsphere, consisting only of epithelia corresponding to the germ-layers,\nand of mesenchyme between them, and then, after a certain period of\nrest, a new organisation will appear. Now this new organisation is\nnot that of a branchial apparatus but represents a very small but\ncomplete ascidian (Fig. 13). Such a fact certainly seems to be very\nimportant, not to say very surprising; but still another phenomena may\nbe demonstrated on the animal which seems to be even more important. You\nfirst isolate the branchial apparatus from the other part of the body,\nand then you cut it in two, in whatever direction you please. Provided\nthey survive and do not die, as indeed many of them do, the pieces\nobtained by this operation will each lose their organisation, as did the\nwhole branchial apparatus, and then will each acquire another one, and\nthis new organisation is also that of a *complete* little *Clavellina*.\nSo we see that not only is the branchial apparatus of our animal capable\nof being transformed into a whole animal by the co-operative work of\nall its parts, but even each part of it may be transformed into a small\n*whole*, and it is quite at our disposal how large this part shall be,\nand what sort of a fragment of the original branchial apparatus it shall\nrepresent.\n\n[Illustration: Fig. 13.--Clavellina.\n\n*a.* Diagram of the normal animal: *E* and *J* = openings; *K* =\nbranchial apparatus; *D* = intestine; *M* = stomach; *H* = heart.\n\n*b.* The isolated branchial apparatus.\n\n*c-e.* Different stages of reduction of the branchial apparatus.\n\n*f.* The new *whole* little ascidian.]\n\nWe could hardly imagine a better instance of an harmonious-equipotential\nsystem.\n\nI cannot give you a description of all the other types of our systems\nsubservient to restitution, and I can only mention here that the common\nhydra and the flatworm *Planaria* are very fine examples of them. But\nto one special case of harmonious equipotentiality you must allow me to\ndirect your further attention.\n\nIt has been known for many years that the Protozoa are also capable of\na restoration of their form and organisation after disturbances, if at\nleast they contain a certain amount of their nuclear substance. This\nprocess of restoration used to be regarded as belonging to the common\ntype of regeneration proper, until T. H. Morgan succeeded in showing\nthat in the genus *Stentor* it follows just the very lines which we know\nalready from our study of embryonic organs or from *Tubularia*; that\nan harmonious-equipotential system is at the basis of what goes on.\nNow, you know that all Protozoa are but one highly organised cell: we\nhave therefore here an instance where the so-called \u201celements\u201d of our\nharmonious-morphogenetic system are not cells, but something inside of\ncells; and this feature must appear to be of very great moment, for it\nfirst shows, as we have already pointed out on another occasion, that\nmorphogenesis is not dependent on cell-division, and it states at the\nsame time that our concept of the harmonious-equipotential system may\ncover a very great area--that, in fact, it is a scheme of a very wide\nextent.\n\n\n*The Problem of the Factor* E\n\nWe turn back again to considerations of a more abstract form. We left\nour analysis of the differentiation of the harmonious-equipotential\nsystems, and particularly of the phenomena of localisation during this\ndifferentiation, at the point where we had succeeded in obtaining an\nequation as the expression of all those factors on which the prospective\nvalue, the actual fate, of any element of our systems depends, *p.v. (X)\n= f(s, l, E)* was the short expression of all the relations involved;\n*s* and *l*, the absolute size of the system and the relative position\nof the element with respect to some fixed points, were independent\nvariables; *E* was a constant, namely, the prospective potency, with\nspecial regard to the proportions embraced by it.\n\nWe shall now study the significance of the factor *E*.\n\nWhat does this *E* mean? Is it a short expression merely for an actual\nsum of elemental agents having a common resultant? And, if so, of what\nkind are these agents? Or what may *E* mean, if it can be shown *not* to\nbe a short sign for a mere sum?\n\n\n*No Explanation Offered by \u201cMeans\u201d or \u201cFormative Stimuli\u201d*\n\nFor practical purposes it seems better if we modify the statement of our\nquestion. Let us put it thus: *E* is one of the factors responsible,\namong variables, for the localisation of organic differentiation;\nwhat then do we actually know about the causal factors which play a\nlocalising part in organogenesis? We, of course, have to look back to\nour well-studied \u201cformative stimuli.\u201d These stimuli, be they \u201cexternal\u201d\nor \u201cinternal,\u201d come from without with respect to the elementary organ\nin which any sort of differentiation, and therefore of localisation,\noccurs: but in our harmonious systems no localising stimulus comes from\nwithout, as was the case, for instance, in the formation of the lens of\nthe eye in response to the optical vesicle touching the skin. We know\nabsolutely that it is so, not to speak of the self-evident fact that the\ngeneral \u201cmeans\u201d of organogenesis have no localising value at all.[61]\n\n[61] One might object here that in a piece of a *Tubularia* stem, for\ninstance, the tissues are in direct contact with the sea-water at\nthe two points of the wounds only, and that at these very points a\nstimulus might be set up--say by a process of diffusion--which gradually\ndecreases in intensity on its way inward. And a similar argument might\napply to the small but whole blastula of Echinus, and to all other\ncases. But, in the first place, stimuli which only differ in intensity\ncould hardly call forth the typical and typically localised single\nfeatures realised in differentiation. On the other hand--and this will\noverthrow such an hypothesis completely--the dependence of the single\nlocalised effects in every case on the *absolute size* of the fragment\nor piece chosen for restoration renders quite impossible the assumption\nthat all the singularities in the differentiation of the harmonious\nsystems might be called forth by single stimuli originating in two\nfixed places in an *independent* way. These would never result in any\n\u201charmonious,\u201d any proportionate structure, but a structure of the\n\u201cnormal\u201d proportionality *and size* at its two ends and non-existent in\nthe middle!\n\nSo we see there is nothing to be done, either with the means or with the\nformative stimuli; both are entirely unable to account for those kinds\nof localisation during differentiation which appear in our harmonious\nsystems.\n\nBut is there no possibility of explaining the phenomena of organogenetic\nlocalisation by any other sort of interaction of parts? Two such\npossibilities may at the first glance seem to exist.\n\n\n*No Explanation Offered by a Chemical Theory of Morphogenesis*\n\nThough never set forth, in the form of a properly worked-out theory,\nthe view has sometimes been advocated by biologists, that a chemical\ncompound of a very high degree of complication might be the very basis\nof both development and inheritance, and that such a chemical compound\nby its disintegration might direct morphogenesis.\n\nLet us first examine if such a view may hold for the most general\nfeatures of organic morphogenesis. It seems to me that from the very\nbeginning there exists one very serious objection to every chemical\ntheory of form-building, in the mere fact of the possibility of the\nrestoration of form starting from atypical localities. The mere fact,\nindeed, that there is such a thing as the regeneration of a leg of a\nnewt--to say nothing about restitution of the harmonious type--simply\ncontradicts,[62] it seems to me, the hypothesis, that chemical\ndisintegration of one compound may govern the course of morphogenetic\nevents: for whence comes the re-existence of the hypothetical compound,\nnewly to be disintegrated, after disintegration *has* been completed\nonce already? And we even know that regeneration may go on several times\nrunning from the same locality!\n\n[62] See my article in *Biolog. Centralblatt*, 27, 1907, p. 69. The\nquestion is rendered still more complicated by the fact that in the case\nof the regeneration, say, of a leg it is not the original \u201cmorphogenetic\ncompound\u201d which is again required for disintegration, after it has\nbecome disintegrated once already, but only a specific part of it: just\nthat part of it which is necessary for producing the leg! On the other\nhand, it would be impossible to understand, on the basis of physical\nchemistry, how the isolated branchial apparatus of *Clavellina* could\nbe transformed, by chemical processes exclusively, into a system of\nwhich only a certain *part* consists of that substance of which the\nstarting-point had been composed in its *completeness*.\n\nBut, if we intentionally disregard this difficulty, in spite of\nits fundamental character, how could the hypothesis of chemical\ndisintegration give the reason for the differentiation of our\nharmonious-equipotential systems, with special regard to the\nlocalisation of it; how could it account, in other words, for the\nappearance of typically localised specifications in an organ for which\nno external localising causes can be predicated?\n\nLet us remember that a few original intimate differences exist in our\nharmonious systems: the main directions of the intimate protoplasmic\nstructure including polarity and bilaterality. There are therefore\nthree times two specified poles in each of these systems, at least in\nbilateral organisms, but no other differences are present in them.\nA few very simple cases of harmonious differentiation might indeed\nbe understood on the theory of a disintegrating chemical compound\nin connection with these few differences. Imagine that the original\ncompound, of the quantity *a*, is disintegrated to the amount of\n*a*_1; from *a*_1 are formed the two more simple compounds, *b*\nand *c*, both of them in definite quantities; then we have the three\nchemical individuals, *a-a*_1, *b* and *c*, as the constituents of\nour harmonious system; and it now might be assumed, without any serious\ndifficulty, though with the introduction of some new hypotheses, that\nthe two poles of one of the fundamental axes of symmetry attract *b* and\n*c* respectively, *a-a*_1 remaining unattracted between them. We thus\nshould have the three elementary constituents of the system separated\ninto three parts, and as they all three are of a definite quantity,\ntheir separation would mean that the system had been divided into three\nparts, *a-a*_1, *b* and *c*, also with regard to its proper form.\nIt is clear, that by taking away any part of the original system, by\nmeans of operations, there would be taken away a certain amount of the\noriginal compound; say that *a/n* is left; then, of course, the three\nconstituents after the partial disintegration would be *a-a_1/n*,\n*b/n* and *c/n*, and so it follows that the proportionality of\nlocalisation would really be preserved in any case.\n\nBut these considerations, evident as they seem to be in the most\nsimple case, fail to satisfy in a really general sense: for two\ndifferent reasons. First, they could never account for the fact that\nthe differentiated organism by no means consists of so many different\ncompounds as it shows single parts of its differentiation, but that,\non the contrary, it only consists, as we know, of a certain rather\nlimited number of true different morphogenetic elements, these\nelements occurring again and again--as for instance, nervous or\nmuscular elements--but typical each time in locality, quantity, and\nform. And in the second place, the very *form* of elementary organs,\ntheir form as such, does not at all go hand-in-hand with chemical\ndifferences; this feature alone would absolutely overthrow any sort\nof a chemical morphogenetic theory to account for the problem of\nlocalisation. Take the typically arranged ring of the mesenchyme\ncells in our Echinus-gastrula, with its two spherical triangles, so\ntypically localised; look at any sort of skeleton, in Radiolaria, or in\nstarfishes, or in vertebrates: here you have form, real form, but form\nconsisting of only one material. Not only is the arrangement of the\nelements of form typical here, *e.g.* the arrangement of the single\nparts of the skeleton of the hand or foot, but also the special form\nof each element is typical, *e.g.* the form of each single bone of the\nfoot; and, on a purely chemical theory of morphogenesis the sufficient\nreason for the production of typical form in such a sense would be\nwanting. For atoms or molecules by themselves can only account for form\nwhich is arranged, so to speak, according to spatial geometry--as in\nfact they do in crystallography; but they can never account for form\nsuch as the skeleton of the nose, or hand, or foot. You will answer\nme perhaps, that there may be non-chemical agents in the germ,[63]\nresponsible for typical form-localisation, but by such reasoning you\nwould be departing from a purely chemical theory. Our next paragraph\nwill be devoted to this side of the question.\n\n[63] Besides the specified poles determined by the polar-bilateral\nstructure of the protoplasm.\n\nThat is the principal reason for rejecting all sorts of chemical\nmorphogenetic theories put forward to explain the problem of\nlocalisation; it is more explicit, and therefore, I suppose, still\nmore convincing than the more general consideration that the very\nfact of restitutions in itself must contradict the hypothesis that\na disintegration of compounds might be the directive agency in\nmorphogenesis. To sum up: Specificity of organic form does not go\nhand-in-hand with specificity of chemical composition, and therefore\ncannot depend on it; and besides that, specific organic form is such\nthat it can never be explained by atomic or molecular arrangement in\nthe chemical sense; for, to state it in a short but expressive manner,\nthe \u201cform\u201d of an atom or molecule can never be that of a lion or a\nmonkey. To assume that would be to go beyond the limits of chemistry in\nchemistry itself.\n\n\n*No Machine Possible Inside the Harmonious Systems*\n\nAnd now we turn to the last possibility which is left to us in our\nendeavour to \u201cunderstand\u201d the localisation of the differentiation in our\nharmonious-equipotential systems by the means of physics and chemistry.\nOutside causes have failed to account for it, chemical disintegration\nof a compound has failed too. But could there not exist some sort of\ncomplicated interactions amongst the parts of the harmonious system\nthemselves? Could there not exist some kind of a real machine in the\nsystem, which, if once set going, would result in the differentiations\nthat are to take place? Then we might say that the \u201cprospective\npotency\u201d of the system is in fact that machine; we should know what the\nletter *E* of our equation stood for: viz., a resultant action of many\ncomplicated elemental interactions, and nothing more.\n\nWeismann, we know already, had assumed that a sort of machine was the\nprime mover of morphogenesis. We have seen that his theory cannot be\ntrue; the results of experiments most strongly contradict it. But, of\ncourse, the experiments only showed us that *such* a machine as *he*\nhad imagined to exist could not be there, that development could not be\ngoverned by the disintegration of a given complicated structure into its\nsimplest parts. But might not some other machine be imaginable?\n\nWe shall understand the word \u201cmachine\u201d in a most general sense. A\nmachine is a typical configuration of physical and of chemical\nconstituents, by the acting of which a typical effect is attained.\nWe, in fact, lay much stress upon embracing in our definition of a\nmachine the existence of chemical constituents also; we therefore\nunderstand by the word \u201cmachine\u201d a configuration of a much higher\ndegree of complication than for instance a steam-engine is. Of course\na machine, whose acting is to be typical with regard to the three\ndimensions in space, has to be typically constructed with regard to\nthese three dimensions itself; a machine that was an arrangement of\nelements in a strict plane could never have typical effects at right\nangles to that plane. This is a point which must well be kept in mind\nin all hypothetical considerations about machines that claim to explain\nmorphogenesis.\n\nIt must be granted that a machine, as we understand the word, might very\nwell be the motive force of organogenesis in general, if only normal,\nthat is to say, if only undisturbed development existed, and if a taking\naway of parts of our systems led to fragmental development.\n\nBut we know that, at least in our harmonious-equipotential systems,\nquite another process occurs after parts have been taken away: the\ndevelopment that occurs is not fragmental but whole, only on a smaller\nscale.\n\nAnd we know, further, that this truly whole development sets in\nirrespective of the amount and direction of the separation. Let us first\nconsider the second of these points. There may be a whole development\nout of each portion of the system--above certain limits--which is, say,\nof the volume *V*. Good! Then there ought to exist a machine, like\nthat which exists in the whole undisturbed system, in this portion *V*\nalso, only of smaller dimensions; but it also ought to exist in the\nportion *V*_1 which is equal to *V* in amount, and also in *V*_2, in\n*V*_3, *V*_4 and so on. Indeed, there do exist almost indefinitely\nmany *V*_n all of which can perform the whole morphogenesis, and all\nof which therefore ought to possess the machine. But these different\nportions *V*_n are only partly different from each other in spatial\nrelation. Many parts of *V*_2 are also parts of *V*_1 and of *V*_3\nand of *V*_4 and so on; that is to say, the different volumes *V*_n\noverlap each other successively and in such a manner that each following\none exceeds the preceding one in the line by a very small amount only.\nBut what then about our machines? Every volume which may perform\nmorphogenesis completely must possess the machine in its totality. As\nnow every element of one volume may play any possible elemental r\u00f4le in\nevery other, it follows that each part of the whole harmonious system\npossesses any possible elemental part of the machine equally well, all\nparts of the system at the same time being constituents of different\nmachines.\n\nA very strange sort of machine indeed, which is the same in all its\nparts (Fig. 14)!\n\n[Illustration: Fig. 14.--An \u201cHarmonious-equipotential System\u201d of\nwhatever kind.\n\nAccording to the \u201cmachine-theory\u201d of life this system ought to possess\na certain unknown very complicated machine *in its completeness*:\n\n      (*a*) in its total length,\n  and (*b*) in each of the equal volumes *v*, *v*_1, *v*_2, *v*_3 and\n    so on,\n  and (*c*) in each of the unequal volumes *w*, *x*, *y*, and so on,\n  and (*d*) in every imaginable volume, no matter of what size.\n\nTherefore the \u201cmachine-theory\u201d of life is absurd.]\n\nBut we have forgotten, I see, that in our operation the absolute amount\nof substance taken away from the system was also left to our choice.\nFrom this feature it follows that not only all the different *V*_n,\nall of the same size, must possess the hypothetic machine in its\ncompleteness, but that all amounts of the values *V*_n-*n*, *n* being\nvariable, must possess the totality of the machine also: and all values\n*V*_n-*n*, with their variable *n*, may again overlap each other.\n\nHere we are led to real absurdities!\n\nBut what is the conclusion of our rather wild considerations?\n\nIt seems to me that there is only one conclusion possible. If we\nare going to explain what happens in our harmonious-equipotential\nsystems by the aid of causality based upon the constellation of single\nphysical or chemical factors and events, there *must* be some such\nthing as a machine. Now the assumption of the existence of a machine\nproves to be absolutely absurd in the light of the experimental facts.\n*Therefore there can be neither any sort of a machine nor any sort of\ncausality based upon constellation underlying the differentiation of\nharmonious-equipotential systems.*\n\nFor a machine, typical with regard to the three chief dimensions\nof space, cannot remain itself if you remove parts of it or if you\nrearrange[64] its parts at will.\n\n[64] The pressure experiments and the dislocation experiments come into\naccount here; for the sake of simplicity they have not been alluded to\nin the main line of our argument.\n\nHere we see that our long and careful study of morphogenesis has been\nworth while: it has afforded us a result of the very first importance.\n\n\n*The Autonomy of Morphogenesis Proved*\n\nNo kind of causality based upon the constellations of single physical\nand chemical acts can account for organic individual development; this\ndevelopment is not to be explained by any hypothesis about configuration\nof physical and chemical agents. Therefore there must be something\nelse which is to be regarded as the sufficient reason of individual\nform-production. We now have got the answer to our question, what\nour constant *E* consists in. It is not the resulting action of a\nconstellation. It is not only a short expression for a more complicated\nstate of affairs, it expresses *a true element of nature*. Life, at\nleast morphogenesis, is not a specialised arrangement of inorganic\nevents; biology, therefore, is not applied physics and chemistry: life\nis something apart, and biology is an independent science.\n\nAll our results at present, indeed, are negative in their form; our\nevidence was throughout what is called *per exclusionem*, or indirect\nor apagogic. There were excluded from a certain number of possibilities\nall except one; a disjunctive proposition was stated in the form: *E*\nis either this, or that, or the other, and it was shown that it could\nnot be any of all these except one, therefore it was proved to be that\none. Indeed, I do not see how natural science could argue otherwise;\nno science dealing with inorganic phenomena does; something new and\nelemental must always be introduced whenever what is known of other\nelemental facts is proved to be unable to explain the facts in a new\nfield of investigation.\n\nWe shall not hesitate to call by its proper name what we believe we have\nproved about morphogenetic phenomena. What we have proved to be true\nhas always been called *vitalism*, and so it may be called in our days\nagain. But if you think a new and less ambitious term to be better for\nit, let us style it the doctrine of the *autonomy of life*, as proved\nat least in the field of morphogenesis. I know very well that the word\n\u201cautonomy\u201d usually means the faculty of *giving* laws to oneself, and\nthat in this sense it is applied with regard to a community of men;\nbut in our phrase autonomy is to signify the *being subjected* to laws\npeculiar to the phenomena in question. This meaning is etymologically\ndefensible, and besides that I perhaps may remind you of a certain\nchapter of Professor Ward\u2019s Gifford Lectures, in which he holds the view\nthat, psychologically and epistemologically, there is more than a mere\nverbal relation between the civil and the natural \u201claw.\u201d\n\nVitalism then, or the autonomy of life, has been proved by us\nindirectly, and cannot be proved otherwise so long as we follow the\nlines of ordinary scientific reasoning. There can indeed be a sort of\ndirect proof of vitalism, but now is not the time to develop this proof,\nfor it is not of the purely scientific character, not so na\u00efve as our\npresent arguments are, if you choose to say so. An important part of our\nlectures next summer will be devoted to this direct proof.\n\n\n\u201c*Entelechy*\u201d\n\nBut shall we not give a name to our vitalistic or autonomous factor\n*E*, concerned in morphogenesis? Indeed we will, and it was not without\ndesign that we chose the letter *E* to represent it provisionally. The\ngreat father of systematic philosophy, Aristotle, as many of you will\nknow, is also to be regarded as the founder of theoretical biology.\nMoreover, he is the first vitalist in history, for his theoretical\nbiology is throughout vitalism; and a very conscious vitalism indeed,\nfor it grew up in permanent opposition to the dogmatic mechanism\nmaintained by the school of Democritus.\n\nLet us then borrow our terminology from Aristotle, and let that factor\nin life phenomena which we have shown to be a factor of true autonomy be\ncalled *Entelechy*, though without identifying our doctrine with what\nAristotle meant by the word \u03ad\u03bd\u03c4\u03b5\u03bb\u03ad\u03c7\u03b5\u03b9\u03b1. We shall use this word only as a\nsign of our admiration for his great genius; his word is to be a mould\nwhich we have filled and shall fill with new contents. The etymology of\nthe word \u1f10\u03bd\u03c4\u03b5\u03bb\u03ad\u03c7\u03b5\u03b9\u03b1 allows us such liberties, for indeed we have shown\nthat there is at work a something in life phenomena \u201cwhich bears the end\nin itself,\u201d \u1f43 \u1f14\u03c7\u03b5\u03b9 \u1f10\u03bd \u1f11\u03b1\u03c5\u03c4\u1fa3 \u03c4\u1f78 \u03c4\u03ad\u03bb\u03bf\u03c2.\n\nOur concept of entelechy marks the end of our analysis of individual\nmorphogenesis. Morphogenesis, we have learned, is \u201cepigenesis\u201d not only\nin the descriptive but also in the theoretical sense: manifoldness\nin space is produced where no manifoldness was, real \u201cevolutio\u201d is\nlimited to rather insignificant topics. But was there nothing \u201cmanifold\u201d\nprevious to morphogenesis? Nothing certainly of an *extensive*\ncharacter, but there was something else: there was entelechy, and thus\nwe may provisionally call entelechy an \u201c*intensive manifoldness*.\u201d\nThat then is our result: not evolutio, but epigenesis--\u201cepigenesis\nvitalistica.\u201d\n\n\n*Some General Remarks on Vitalism*\n\nWe now shall leave entelechy where it stands: next summer we shall turn\nback to it and shall make its full logical and ontological analysis\nour chief study. At present we are satisfied with having proved its\nexistence in nature, with having laid some of the foundations of a\ndoctrine to be based upon it. I hope that these foundations will evince\nthemselves strong: that is all-important.[65] It indeed has been the\nfault of all vitalism in the past that it rested on weak foundations.\nTherefore the discussion of the basis underlying our doctrine of the\nautonomy of life is to occupy us still a considerable time. We shall\ndevote to it two more of this year\u2019s lectures and three of the next; we\nshall examine all sorts of phenomena of life in order to find out if\nthere are any further proofs of vitalism, independent perhaps, of what\nwe way call our *first proof*, which is based upon the analysis of the\n*differentiation of harmonious-equipotential systems*. We shall find\nsome more independent proofs; and besides that we shall find many kinds\nof phenomena upon which future times perhaps may erect more of such\nindependent proofs.\n\n[65] My \u201cfirst proof of vitalism\u201d was first developed in the paper, \u201cDie\nLocalisation morphogenetischer Vorg\u00e4nge,\u201d Leipzig, 1899. (See additional\nremarks in *Organische Regulationem*, Leipzig, 1901, and in *Archiv\nf\u00fcr Entwickelungsmechanik*, 14, 1902.) I cannot admit that any really\nserious objection has been brought forward against it. (See my articles\nin *Biologisches Centralblatt*, 22, 23, 27, and in *Ergebnisse d. Anat.\nu. Entwickelungsgesch*. 11, 14.) An historical sketch of vitalism will\nbe found in my book, *Der Vitalismus als Geschichte und als Lehre*,\nLeipzig, 1905.\n\nFor we shall be chary of bestowing the name \u201cproof\u201d except on what is a\nproof indeed, of course according to our critical conviction. Vitalistic\nviews in biology have arisen in rather numerous forms during the last\nfifteen years, especially in Germany--though in very strong contrast to\nthe so-called official German biology--but I can only admit that one of\nall the arguments of \u201cneo-vitalism\u201d has proved its statements. I refer\nto the theory of \u201cmorphaesthesia\u201d as developed by Noll, which we shall\nstudy briefly in the next lecture. I cannot concede that Reinke or\nSchneider or Pauly have really proved what they believe, and I cannot\neven allow to the most original thinker in this field, Gustav Wolff,\nthat he has given a real demonstration of his views. He states that the\nexistence of so-called \u201cprimary purposefulness,\u201d that is, the existence\nof adaptive processes, which cannot be imagined to have arisen on\nDarwinian principles, is able to prove vitalism; but I say that it only\nproves teleology, which is a broader concept than vitalism.\n\nThe possibility of a machine at the root of the phenomena in question\nalways has to be excluded in order that vitalism may be proved, and I\ncannot grant that the necessity of such an exclusion has been actually\nshown by any of my fellow-combatants against so-called mechanism, except\nNoll.[66]\n\n[66] We are dealing here with morphogenesis and so-called vegetative\nphysiology only; to certain psychologists, who have refuted the theory\nof psycho-physical parallelism, I must grant that they also have proved\nvitalism. (See Volume II.)\n\n\n*The Logic of our First Proof of Vitalism*\n\nLet us devote the end of our present lecture to an account of the\nlogical means by which it has been possible to develop what we hope will\nbe regarded as a true *proof* of life autonomy.\n\nFirstly, we have looked upon the phenomena of morphogenesis without\nany prepossessions; we may say that we have fully surrendered ourselves\nto them; we have not attacked them with any sort of dogmatism except\nthe inherent dogmatism of all reasoning. But this dogmatism, if it may\nbe called so, does not postulate that the results of the inorganic\ndoctrines must hold for the organic world, but only that both the\ninorganic and the organic must be subject to certain most general\nprinciples.\n\nBy studying life as a given phenomenon, by fully devoting ourselves to\nour problem, we not only have analysed into its last elements what was\ngiven to us as our subject, but we also, more actively, have created new\ncombinations out of those elements: and it was from the discussion of\nthese positive constructions that our argument for vitalism was derived.\n\nWe have analysed morphogenesis into elementary processes, means,\npotency, formative stimulus, just as the physicist analyses mechanics\ninto time, velocity, mass, and force; we have then rearranged\nour elements into \u201csystems\u201d--the equipotential systems, the\nharmonious-equipotential system in particular, just as the physicist\ncomposes his elements into the concepts of momentum or of kinetic energy\nor of work. And finally, we have discussed our compositions and have\nobtained our result, just as the physicist gets his ultimate results by\ndiscussing work and kinetic energy and momentum.\n\nOf course the comparison is by no means intended to show that mechanics\nand biology are sciences of the same kind. In my opinion, they are not\nso at all; but nevertheless there do exist similarities of a logical\nkind between them.\n\nAnd it is not the formal, logical character alone which allows us to\ncompare biology with other natural sciences: there is still something\nmore, there is one kind of assumption or postulate, or whatever you\nmay choose to call it, without which all science whatever would be\naltogether *impossible*. I refer to the concept of *universality*. All\nconcepts about nature which are gained by positive construction out of\nelements resulting from analysis, claim to be of *universal validity*;\nwithout that claim there could indeed be no science.\n\nOf course this is no place for a lecture on methodology, and it\ntherefore must suffice to make one remark with special regard to\nour purpose, which we should like to emphasise. Our concept of the\nharmonious-equipotential system--say rather, our concept of the\nprospective potency itself--presumes the understanding that indeed *all*\nblastomeres and *all* stems of *Tubularia*, including those upon which\nwe have *not* carried out our experiments, will behave like those we\nhave experimented with; and those concepts also presume that a certain\ngerm of Echinus, *A*, the blastomeres of which were not separated,\nwould have given two whole larvae, if separation had taken place, while\nanother germ, *B*, which actually gave us two larvae after separation,\nwould only have given one without it. Without this presumption the\nconcept of \u201cpotency\u201d is meaningless, and, indeed, every assumption of a\n\u201cfaculty\u201d or a \u201cpossibility\u201d would be meaningless in the whole area of\nscience.\n\nBut this presumption can never be proved; it can only be postulated. It\ntherefore is only with this postulate that our first proof of vitalism\nholds; but this restriction applies to *every* law of nature.\n\nI cannot force you to agree with this postulate: but if you decline\nyou are practically saying that there exists a sort of pre-established\nharmony between the scientific object and the scientist, the scientist\nalways getting into his hands such objects only as have been\npredestinated from the very beginning to develop two larvae instead of\none, and so on.\n\nOf course, if that is so, no proof of natural laws is possible at all;\nbut nature under such views would seem to be really d\u00e6monic.\n\nAnd so, I hope, you will grant me the postulate of the universality\nof scientific concepts--the only \u201chypothesis\u201d which we need for our\nargument.\n\n\n4. ON CERTAIN OTHER FEATURES OF MORPHOGENESIS ADVOCATING ITS AUTONOMY\n\nOur next studies on the physiology of form will be devoted in the first\nplace to some additional remarks about our harmonious-equipotential\nsystems themselves, and about some other kinds of morphogenetic\n\u201csystems\u201d which show a certain sort of relationship with them. For it is\nof the greatest importance that we should become as familiar as possible\nwith all those facts in the physiology of form upon the analysis of\nwhich are to be based almost all of the future theories that we shall\nhave to develop in biology proper and philosophical. Our discussions, so\nfar as they relate to questions of actual fact, will contain only one\nother topic of the same importance.\n\nBut though it is designed to complete and to deepen our analysis,\nthe present considerations may yet be said to mark a point of rest\nin the whole of our discussions: we have followed one single line of\nargumentation from the beginning until now; this line or this stream of\nthought, as you might call it, is now to break into different branches\nfor a while, as if it had entered from a rocky defile into a plain.\nIt seems to me that such a short rest will be not unconducive to a\nright understanding of all we have made out; and such a full and real\nconceiving again, such a realising of our problems of morphogenesis and\ntheir solutions, will be the best preparation for the philosophical part\nof these lectures.\n\n\nHARMONIOUS-EQUIPOTENTIAL SYSTEMS FORMED BY WANDERING CELLS\n\nAll of the harmonious-equipotential systems which we have studied so\nfar were the bases of histological differentiation; that is to say, the\nprocesses of their differentiation consisted in specifically localised\nelements of theirs becoming different *in situ*. Now we know at least\none type of systems which also may be called harmonious-equipotential,\nbut the differentiation of which does not simply relate to elements at\na fixed place. An additional phenomenon enters here into the sphere of\nthe others. The elements not only become different where they are, but\na specific changing of locality, a specific kind of wandering, goes\nhand-in-hand with differences relating to the prospective value to be\nattained. I am speaking of the formation of the larval skeleton of\nour well-known Echinus. We know that the mesenchyme cells, which have\nleft the blastoderm and are arranged in a sort of ring of bilateral\nstructure, are the starting-point of this skeleton: it indeed originates\nin a sort of secretive process on the part of the cells; the cells\nare moving about and are secreting carbonate of lime during their\nwandering. The experiments now have shown, as we know, that a whole,\nthough smaller, skeleton may also be formed, if only a half or a quarter\nof the mesenchyme cells are present, as happens to be the case in all\nexperiments with isolated blastomeres of the two or four-cell stage of\ncleavage. It is clear that in these cases the performance of each single\ncell must be different from what it is in the normal case, and that\nthe same sort of differences in the morphogenetic performances appears\nagain, if the two- and the four-cell stage are compared with each other.\nAnd there are still some other phenomena showing the possibility of\ndifferent performances being carried out by the individual cells. Peter\nhas shown that the number of mesenchyme cells may vary enormously under\ncertain conditions; but, in spite of that, the skeleton always will\nbe complete. It may be said that this line of research is only of a\nrelative value to our own questions, as, of course, variability relates\nto different individuals: but it seems to me that it adds a very good\nsupplementary instance to what the experiment on the individual itself\nhas established.\n\nWe should only be repeating ourselves if we were to analyse again what\nhappens here as the expression of the harmonious-equipotentiality\nitself. But indeed there occurs something new in this instance: the\nsingle mesenchyme cell not only has to perform in each case that single\nact of specific secretion which the case requires, but it also has to\nwander to the right place in order to perform it; there must be some\norder, not only about the acts of secretion after wandering, but also in\nthe migrations themselves. If undisturbed ontogeny alone were possible,\nand if therefore a theory like that of Weismann were in place, we might\nsay perhaps that each mesenchyme-cell is specified not only as to its\nperformance in secretion, but also with regard to its chemotactical\nirritability, the latter being typically localised, so that its effect\nbecomes typical, thanks to the typical arrangement of all the cells\nwith respect to each other. But that is certainly not the case. Now, you\nmay ask yourselves if you could imagine any sort of a machine, which\nconsists of many parts, but not even of an absolutely fixed number, all\nof which are equal in their faculties, but all of which in each single\ncase, in spite of their potential equality, not only produce together\na certain typical totality, but also arrange themselves typically in\n*order* to produce this totality. We *are* indeed familiar with certain\noccurrences in nature where such curious facts are observed, but I doubt\nif you would speak of \u201cmachines\u201d in these cases. The mesenchyme-cells,\nin fact, behave just as a number of workmen would do who are to\nconstruct, say, a bridge. All of them *can* do every single act, all of\nthem also *can* assume every single position: the result always is to\nbe a perfect bridge; and it is to be a perfect bridge even if some of\nthe workmen become sick or are killed by an accident. The \u201cprospective\nvalues\u201d of the single workman change in such a case.\n\nI well know that it is only an analogy which I am offering to you.\nThe mesenchyme-cells have not \u201clearned,\u201d have no \u201cexperience.\u201d All\nthat is to occupy us next summer. But in spite of it, there is truth\nin the analogy; and perhaps you will prefer it to the merely abstract\nconsideration.\n\n\nON CERTAIN COMBINED TYPES OF MORPHOGENETIC SYSTEMS\n\nFor the sake of completeness it may be remarked, only by the way, that\nthe type of the proper harmonious-equipotential system may go hand in\nhand with another type of \u201csystems\u201d which play a part in morphogenesis;\na type which we have shortly mentioned already and which will be studied\nfully a few chapters later. We know that there are equipotential systems\nwith complex potencies: that is to say, systems which may produce a\nwhole organism equally well from any one of their elements; we know the\ncambium of Phanerogams to be such a system. Now it is easily understood\nthat the germ of our Echinus, say in the stage of two or four or eight\ncleavage cells, is not only an harmonious-equipotential system, but\na complex-equipotential system too. Not only may there arise a whole\norganism out of 2/4 or 3/4 or 3/8, 4/8, 5/8, 6/8, 7/8 of its elements,\nin which cases the harmonious r\u00f4le of the single element with regard to\nits single performance in a totality is variable, but there may also\narise four whole single larvae out of the four cells of the four-cell\nstage, or eight single whole larvae out of the eight-cell stage.[67]\nIn these cases, of course, each of the four or eight elements has\nperformed not a part of the totality, changing with its \u201cposition,\u201d but\nthe totality itself. With respect to these possible performances the\n\u201csystems\u201d present in the four or eight-cell stages of cleavage must be\ncalled complex-equipotential ones.\n\n[67] The eight larvae would be incomplete in some respect, but not with\nregard to symmetry. They would be \u201cwhole\u201d ones, only showing certain\ndefects in their organisation. See page 65 note 1, and page 73.\n\nWe propose to give the name of *mixed-equipotential systems* to all\nthose equipotential systems which, at the same time, may be regarded\nas belonging to the harmonious or to the complex type. It is not only\namong cleavage-stages that they are to be found; you may also find them\nvery clearly exhibited in our ascidian *Clavellina* for instance. We\nknow already that the branchial apparatus of this form is typically\nharmonious-equipotential, but it is complex-equipotential too, for it\nalso may regenerate what is wanting in the proper way, by a budding\nfrom the wound; and the same is true of many other cases, the flatworm\n*Planaria* for instance.\n\nAnother type of systems, which might be said to be of a higher degree,\nis exhibited in some very strange phenomena of regeneration. It was\nfirst shown most clearly by some experiments of Godlewski\u2019s that a\nwhole tail may be regenerated from a wound inflicted on the body of\na newt, even if this wound involves section of only a portion of the\nbody-diameter. Section of the whole of the body-diameter of course\nwould cause the formation of the whole tail also; but it was found that\neven an incomplete cross-section of the body is capable of performing\nthe whole on a smaller scale. The series of possible cross-sections\nwhich are all capable of regeneration would have to be called a\nsystem of the complex type in this case; but, now we learn that every\n*single* cross-section is of the harmonious type, we must speak of\n*complex-harmonious systems*. What we have described is not the only\ninstance of our new type of morphogenetic systems. Some other instances\nhad been discovered a few years earlier, though nobody had pointed\nout their true significance. In the flatworm *Planaria* a partial\ncross-section is also capable of forming a whole structure, say a head,\nand all cases of so-called \u201csuper-regeneration\u201d after the infliction of\na complicated wound probably belong here also.\n\nYou may say that our two additions to the theory of systems are merely\nformal, and indeed I am prepared to concede that we shall not learn\nanything altogether new from their discussion: their analysis would lead\neither to what was our \u201cfirst proof\u201d of the autonomy of life-phenomena\nor to what will be our \u201csecond\u201d one. But the mere descriptions of the\nfacts discovered here will interest you, I think, and will fill your\nminds with more vivid pictures of the various aspects of form-autonomy.\n\nWhile dealing with our harmonious-equipotential systems as the\nstarting-points of processes of restitution, *e.g.* in *Tubularia*,\n*Clavellina*, the flatworms, and other instances, we always have\nregarded cross-sections of the body as constituting the elements of\nequipotentiality. Now cross-sections, of course, are by no means simple\nin themselves, but are made up of very different tissues, which are\nderivates of all three of the original germ layers--ectoderm, mesoderm,\nand endoderm. Owing to this composite character of the cross-sections,\ntaken as elements of harmonious systems, a special phenomenon of\nmorphogenesis is presented to us, which teaches somewhat more than the\nmere concept of harmonious-equipotentiality can express. If composite\nelements concerned in morphogenesis result in one whole organisation\nin spite of the development of the single tissues of these elements\ngoing on independently, then there must be a sort of correspondence\nor reciprocity of the harmonious development among these tissue\nconstituents themselves; otherwise a proportionate form could not be the\nfinal result. We may conveniently speak of a *reciprocity of harmony* as\nexisting between the single tissues or germ layers which constitute many\nharmonious-equipotential systems, and there can be little doubt that we\nhave here an important feature with regard to general morphogenesis.[68]\n\n[68] Reciprocal harmony may be reduced in some cases to the given\nproportions of one original harmonious system, from which the single\nconstituents of the complicated system, showing reciprocal harmony, are\nderived. Then we have only an instance of \u201charmony of constellation\u201d\n(see p. 109). But reciprocal harmony seems to become a problem itself,\nif it occurs in restitutions starting from quite a typical point,\nselected by the experimenter. It will be a problem of future research\nto give an exact formula of what happens here. Reciprocal harmony also\noccurs in regeneration proper. It is known that the formation of the\nregenerative bud and the differentiation of this bud follow each other.\nAs the bud is composed of different elementary systems, it follows that\nthese different systems, of which every single one is harmonious, also\nhave to work in reciprocity to each other, in order that one whole\nproportionate formation may result.\n\nA few other groups of morphogenetic facts may find their proper place\nhere, though they are not properly to be regarded as additions to the\ntheory of harmonious systems but as forming a sort of appendix to it.\n\n\nTHE \u201cMORPHAESTHESIA\u201d OF NOLL[69]\n\n[69] *Biol. Centralblatt.* 23, 1903.\n\nWe may briefly mention that group of botanical phenomena, by which\nthe botanist Noll has been led to the concept of what he calls\n\u201cmorphaesthesia,\u201d or the \u201cfeeling\u201d for form; a concept, the full\ndiscussion of which would lead to almost the same conclusions as our\nanalysis of the harmonious systems has done. In the Siphoneae, a\nwell-known order of marine algae with a very complicated organisation\nas to their exterior form, the protoplasm which contains the nuclei is\nin a constant state of circulation round the whole body, the latter\nnot being divided by proper cell-walls. On account of this constant\nmovement it is certainly impossible to refer morphogenetic localisation\nto definite performances of the nuclei. Nor can any sort of structure\nin the outer protoplasmic layer, which is fixed, be responsible for\nit, for there is no such structure there: hence there must be a sort\nof feeling on the part of the plant for its relative body localities,\nand on account of this feeling morphogenesis occurs. This \u201cfeeling\u201d is\nstyled \u201cmorphaesthesia\u201d by Noll, and to it he tries to refer all sorts\nof different botanical form-phenomena,[70] for instance what is called\n\u201cautotropism,\u201d that is, the fact that branches of plants always try to\nreassume their proper angle with regard to their orientation on the main\naxis, if this orientation has been disturbed. It may be an open question\nif this particular application of the theory is right: certainly\nthere seems to be much truth in the establishment of the concept of\nmorphaesthesia, and we only have to object to its psychological name.\nBut that may be done in a more general form on a later occasion.\n\n[70] Certain phenomena of the physiology of growth of *Geranium\nRobertianum*, recently discussed by Franc\u00e9 from a vitalistic point of\nview (*Zeitschr. Entw. lehre*. 1, 1907, Heft iv.), might also belong\nhere. I cannot see an independent proof of vitalism in these facts if\ntaken by themselves; a pre-existing \u201cmachine\u201d cannot be absolutely\nexcluded here.\n\n\nRESTITUTIONS OF THE SECOND ORDER\n\nIn the hydroid polyp *Tubularia*, already familiar to us as being a most\ntypical representative of the harmonious-equipotential systems, a very\ninteresting phenomenon has been discovered[71], almost unparalleled at\npresent but nevertheless of a general importance, a phenomenon that\nwe may call a restitution of a restitution, or a restitution of the\nsecond order. You know that the first appearance of the new head of\n*Tubularia*, after an operation, consists in the formation of two rings\nof red lines, inside the stem, these rings being the primordia of the\nnew tentacles. I removed the terminal ring by a second operation soon\nafter it had arisen, disturbing in this way the process of restitution\nitself: and then the process of restitution itself became regulated. The\norganism indeed changed its course of morphogenesis, which was serving\nthe purposes of a restitution, in order to attain its purpose in spite\nof the new disturbance which had occurred. For instance, it sometimes\nformed two rings out of the one that was left to it, or it behaved\nin a different way. As this difference of morphogenetic procedure is\na problem by itself, to be discussed farther on, we shall postpone a\nfuller description of this case of a restitution of the second degree.\n\n[71] Driesch, *Arch. Entw. Mech.* 5, 1897.\n\nAt present I do not see any way of proving independently the autonomy of\nlife by a discussion of these phenomena; their analysis, I think, would\nagain lead us to our problem of localisation and to nothing else; at\nleast in such an exact form of reasoning as we demand.\n\n\nON THE \u201cEQUIFINALITY\u201d OF RESTITUTIONS[72]\n\n[72] Driesch, *Arch. Entw. Mech.* 14, 1902.\n\nI have told you already that *Tubularia* in the phenomena of the\nregulation of restitutions offers us a second problem of a great general\nimportance, the problem of the *Equifinality of Restitutions*. There\nindeed may occur restitutions, starting from one and the same initial\nstate and leading to one and the same end, but using very different\nmeans, following very different ways in the different individuals of one\nand the same species, taken from the same locality, or even colony.\n\nImagine that you have a piece of paper before you and wish to sketch\na landscape. After drawing for some time you notice that you have\nmiscalculated the scale with regard to the size of the paper, and\nthat it will not be possible to bring upon the paper the whole of the\nlandscape you want. What then can you do? You either may finish what you\nhave begun to draw, and may afterwards carefully join a new piece of\npaper to the original one and use that for the rest of the drawing; or\nyou may rub out all you have drawn and begin drawing to a new scale; or\nlastly, instead of continuing as you began, or erasing altogether, you\nmay compromise as best you can by drawing here, and erasing there, and\nso you may complete the sketch by changing a little, according to your\nfancy, the proportions as they exist in nature.\n\nThis is precisely analogous to the behaviour of our *Tubularia*.\n*Tubularia* also may behave in three different ways, if, as I described\nto you, the terminal one of its two newly arisen rings of tentacle\nprimordia is removed again. It may complete what is left, say the basal\ntentacle ring, then put forth from the horny skeleton (the \u201cperisarc\u201d)\nthe new head as far as it is ready, and finally complete this head\nby a regular process of budding regeneration. But it also may behave\ndifferently. It may \u201cerase\u201d by a process of retro-differentiation all\nthat has been left of what had already been formed, and then may form\n*de novo* the totality of the primordia of a new head. Or, lastly, it\nmay remove a part of the middle of the one ring of tentacle rudiments\nwhich was left, and may use this one ring for the formation of two,\nwhich, of course, will not be quite in the normal relations of place\nwith regard to each other and to the whole, but will be regulated\nafterwards by processes of growth. Thus, indeed, there is a sort of\nequifinality of restitution: one starting-point, one end, but three\ndifferent means and ways.\n\nIt would, of course, contradict the principle of univocality, as we\nshall see more fully later on, to assume that there actually are\ndifferent ways of regulation whilst all the conditions and stimuli are\nthe same. We are obliged to assume, on the contrary, that this is not\nthe case, that there are certain differences in the constellation, say\nof the general conditions of age or of metabolism, which are responsible\nfor any given individual choosing one process of restitution instead\nof another; but even then the phenomenon of equifinality remains very\nstriking.\n\nIt has long been known that restitution in general does not always\nfollow the same lines of morphogenesis as are taken by ontogeny, and it\nwas this feature that once led Roux to point out that the adult forms\nof organisms seem to be more constant than their modes of origin. But,\ncomparing ontogeny with restitution in general, we see that only the\nends are the same, not the points of starting; the latter are normal or\nnon-typical in ontogeny, atypical in restitution. In the new discoveries\nof an equifinality of restitutions we have the *same* starting-point,\nwhich is decidedly non-typical but atypical, *i.e.* dependent on our\narbitrary choice, leading by *different* ways always to the *same* end.\n\nThere may be many who will regard the fact of equifinality as a proof of\nvitalism. I should not like to argue in this easy way; I indeed prefer\nto include part of the phenomena of equifinality in our first proof of\nautonomy, and part in the second one, which is to follow.\n\nAnother important phenomenon of the equifinality of regulation was\ndiscovered by Morgan. A species of the flatworm *Planaria* was found to\nrestore its totality out of small pieces either by regeneration proper,\nif the pieces were fed, or by a sort of rearrangement of material,\non the basis of its harmonious-equipotentiality, if they were kept\nfasting. It is important to note that here we see one of the conditions\ndetermining the choice of the way to restoration, as we also do in the\nwell-known equifinal restitutions of the root in plants, where the\nbehaviour of the organism depends on the distance of the operation-wound\nfrom the tip.[73] In *Tubularia* the actual stage of restitution that\nhas been already reached by the stem when the second operation takes\nplace, may account for the specification of its future organogenesis,\nbut this is not at all clearly ascertained at present.\n\n[73] The root may be restored by regeneration proper, or by the\nproduction of adventitious roots, or by one of the side-roots changing\nits geotropism from horizontal to positive, according to the smaller or\ngreater distance of the wound from the tip.\n\n*Clavellina* also shows equifinality in its restitution, as has already\nbeen shortly mentioned. The isolated branchial apparatus may restitute\nitself by retro-differentiation to an indifferent stage followed by\nrenovation; or it may regenerate the intestine-sac in the proper way.\nNothing is known here about the conditions, except perhaps that young\nindividuals seem more apt to follow the first of these two ways, older\nones the second; but there are exceptions to this rule.\n\nThe discussion of other instances of equifinality, though important in\nthemselves, would not disclose anything fundamentally new, and so we may\nclose the subject with the remark that nothing can show better than the\nfact of the equifinality of restitutions how absolutely inadequate all\nour scientific conceptions are when confronted with the actual phenomena\nof life itself. By analysis we have found differences of potencies,\naccording as they are simple or complex; by analysis we have found\ndifferences of \u201csystems,\u201d differences of means, and indeed we were glad\nto be able to formulate these differences as strictly as possible: but\nnow we see how, in defiance of our discriminations, one and the same\nspecies of animals behaves now like one sort of our \u201csystems,\u201d and now\nlike the other; how it uses now one sort of \u201cpotencies,\u201d now another.\n\nBut even if it is granted that, in the presence of such phenomena of\nlife, our endeavour seems to be like a child\u2019s play on the shores of the\nocean, I do not see any other way for us to go, so long, at least, as\nour goal is human science--that is, a study of facts as demanded by our\nmental organisation.\n\n\nREMARKS ON \u201cRETRO-DIFFERENTIATION\u201d\n\nWe shall finish this part of our studies by mentioning a little more\nexplicitly one fundamental fact which has already entered incidentally\ninto our considerations, viz. *retro-* or *back-differentiation*.[74]\nWe know that it occurs in *Clavellina* and in *Tubularia*; we may add\nthat it also happens in *Hydra*, and that in the flatworm *Planaria*\nthe pharynx, if it is too large for a piece that is cut out, may be\ndifferentiated back and be replaced by a new pharynx, which is smaller.\n\n[74] \u201cRetro\u201d-differentiation, of course, is not \u201cRe\u201d-differentiation\n(\u201cUmdifferenzierung,\u201d see p. 111), though it may help it to occur.\n\nIt is not death and sloughing of parts that occurs in these cases,[75]\nbut a real process of active morphogenesis; not, however, a process\nconsisting in the production of visible manifoldness, but the opposite.\nLoeb was the first to lay much stress upon this topic, and indeed, there\nmay appear a very strange problem in its wake: the problem, whether\n*all* morphogenesis might be capable perhaps of going backwards under\ncertain conditions.\n\n[75] Of course such a real decay of parts may happen in other cases.\n\nIt is important to note that in most[76] cases retro-differentiation\noccurs in the service of restitution: it goes on wherever restitution\nrequires it. This fact alone would show that not very much could be\nexplained here by the discovery of modern chemistry, important as\nit is, that one and the same \u201cferment\u201d or \u201cenzyme\u201d may affect both\nthe composition and the decomposition of the same compound. We could\nregard what is called \u201ccatalysis\u201d solely as an agent in the service of\nentelechy. But this point also will become clearer in another part of\nthe work.\n\n[76] Certain cases of retro-differentiation occurring under conditions\nof strict fasting will be described in a later chapter.\n\n\n\n\n*C.* ADAPTATION\n\nINTRODUCTORY REMARKS ON REGULATIONS IN GENERAL\n\n\nWe have finished our long account of individual morphogenesis proper.\nIf we look back upon the way we have traversed, and upon those topics\nin particular which have yielded us the most important general results,\nthe material for the higher analysis which is to follow, it must\nstrike us, I think, that all these results relate to regulations.\nIn fact, it is \u201csecondary\u201d form-regulations, according to our\nterminology, that we have been studying under the names of equifinality,\nback-differentiation, restitution of the second order, and so on, and\nour harmonious-equipotential systems have figured most largely in\nprocesses of secondary form-regulations also. But even where that has\nnot been the case, as in the analysis of the potencies of the germ in\ndevelopment proper, form-regulations of the other type have been our\nsubject, regulations of the primary or immanent kind, the connection\nof normal morphogenetic events being regulatory in itself. It was not\nthe phenomenon of organic regulation as such that afforded us the\npossibility of establishing our proof of the autonomy of morphogenesis:\nthat possibility was afforded us by the analysis of the distribution of\npotencies; but upon this distribution regulation is based, and thus\nwe may be said to have studied some types of regulation more or less\nindirectly when analysing potencies.\n\nIt therefore seems to me that we shall have hopes of a successful issue\nto our inquiries, if we now, on passing to what is called the physiology\nof the vegetative functions, proceed to focus our attention on the\nconcept of regulation as such. And that is what we shall do: on our\nway through the whole field of physiology, we shall always stop at any\noccurrence that has any sort of regulatory aspect, and shall always ask\nourselves what this feature has to teach us.\n\nBut let us first try to give a proper definition of our concept. We\nshall understand by \u201cregulation\u201d any occurrence or group of occurrences\non a living organism which takes place after any disturbance of\nits organisation or normal functional state, and which leads to a\nreappearance of this organisation or this state, or at least to a\ncertain approach thereto. Organisation is disturbed by any actual\nremoval of parts; the functional state may be altered by any change\namong the parts of the organism on the one hand, by any change of the\nconditions of the medium on the other; for physiological functioning\nis in permanent interaction with the medium. It is a consequence of\nwhat we have said that any removal of parts also changes the functional\nstate of the organism, but nevertheless organisation is more than a mere\nsum of reactions in functional life. All regulations of disturbances\nof organisation may be called *restitutions*, while to regulations of\nfunctional disturbances we shall apply the name *adaptations*. It is\nwith *adaptations* that we have to deal in the following.\n\nLet us begin our studies of adaptations in a field which may justly\nbe called a connecting link between morphogenesis and physiology\nproper, not yet wholly separated from the science of the organic form,\nmorphology.\n\n\n1. MORPHOLOGICAL ADAPTATION\n\n*Morphological adaptation* is a well-established fact, and I need only\nmention the striking differences between the land and water form of\namphibious plants, or the differences between the same species of plants\nin the Alps and in the plains, or the very different aspect of the arms\nof an athlete and of an ascetic, to recall to your memory what is meant\nby this term.\n\nMorphological adaptation is no part of individual morphogenesis proper,\nbut occurs at the end of it; at least it never occurs previous to the\nfull individual life of an organism, previous to its true functional\nlife; for it relates to the functions of the complete organism.\n\n\nTHE LIMITS OF THE CONCEPT OF ADAPTATION\n\nIt is especially, though by no means exclusively, among plants that\nmorphological adaptation assumes its most marked forms; and this topic,\nindeed, may very easily be understood if we remember that plant-life\nis in the very closest permanent dependence on the medium, and that\nthis medium is liable to many changes and variations of all kinds.\nIn order to elucidate our problem, it therefore seems convenient to\nrestrict our considerations for a while to the study of plants. There\nexist very many external formative stimuli in the morphogenesis of\nvegetation: would it then be possible to regard every effect of such\nan external formative stimulus as a real morphological adaptation?\nNo; for that would not meet the point. The general *harmony* of form\nis indeed concerned if gravity forces roots to shoot forth below at a\nspot where they can enter the ground, or if light induces branches and\nleaves to originate at places where they can obtain it for assimilation;\nbut gravity and light themselves are mere formative stimuli--of the\nlocalising type--in these instances, for they relate only to the\nindividual production of form, not to the functioning of already\nexisting form. We therefore are warned not to confuse the effects of\nformative stimuli from without with real adaptive effects until we have\nfully analysed the particular case.\n\nWe have drawn a sharp line between causes and means of morphogenesis,\napplying the term \u201cmeans\u201d to those conditions of the morphogenetic\nprocess which relate neither to the specificity nor to the localisation\nof its constituents, though they are necessary for the accomplishment\nof the process in the most thorough manner. Would it be possible to\nconnect our new concept of an adaptation with our well-established\nconcept of a means of morphogenesis in such a way that we might speak\nof a morphological \u201cadaptation\u201d whenever any specific feature about\nmorphogenesis proves to be immediately dependent for its success on some\nspecific means, though it does not owe its localisation to that means\nas its \u201ccause\u201d? It seems to me that such a view would also fall wide\nof the mark. It is well known, for instance, that the flowers of many\nplants never fully develop in the dark; light is necessary for their\nmorphogenesis. Is, therefore, their growth in the presence of light to\nbe called a morphological \u201cadaptation\u201d to light? Certainly not: they\nsimply *cannot* originate without light, because they require it for\nsome reason. It is precisely here that our conception of light as a\n\u201cmeans\u201d of morphogenesis is most fully justified. There are many[77]\nsuch cases; and there are still others of an apparently different\ntype, but proving the same. All pathological forms produced in plants\nby animal parasites or by parasitic fungi could hardly be called\nadaptations, but must be attributed to some abnormality of means or of\nstimuli. It may be that the organism reacts as well as possible in these\ncases, and that if it reacted otherwise it would die--we know absolutely\nnothing about this question. But even then there would only be some sort\nof regulation *in* the process of pathological morphogenesis, but *the\nprocess* itself could hardly be called adaptive.\n\n[77] Klebs has suppressed the reproductive phase of organisation\naltogether, in fungi as well as in flowering plants, or has made it\noccur abnormally early, merely by changing the \u201cexternal conditions\u201d\nand by altering the \u201cinternal\u201d ones correspondingly. There is hardly\nanything like an adaptation in these cases, which, by the way, offer\ncertain difficulties to analysis, as the boundaries between \u201ccause\u201d and\n\u201cmeans\u201d are not very sharp here.\n\nSo far we have only learned what is not to be regarded as morphological\nadaptation. No response to external formative stimuli is in itself an\nexample of adaptation, nor are processes dependent for their existence\non any kind of condition or means to be called, simply because they are\ndependent on them, adaptations to those agents. What then, after all, is\na morphological adaptation?\n\nLet us remember what the word adaptation is really to mean in our\ndiscussions: a state of functioning is adapted--a state of functioning\nmust therefore have been disturbed; but as functioning itself, at least\nin plants, certainly stands in close relations to the medium, it follows\nthat all adaptations are in the last resort connected with those factors\nof the medium which affect functioning. In being correctives to the\ndisturbances of functioning they become correctives to the disturbing\nfactors themselves.\n\nBut again, the question seems to arise whether these factors of the\nmedium, when they provoke an adaptation by some change that is followed\nby functional disturbance, do so in the capacity of \u201ccauses\u201d or of\n\u201cmeans,\u201d and so it might seem that we have not gained very much so far\nby our analysis. The reproach, however, would not be quite justified,\nit seems to me: we indeed have gained a new sort of analytical concept,\nin the realm of causal concepts in general, by clearly stating the\npoint that adaptations are related directly to functionality, and only\nindirectly, through functionality, to external changes. By the aid of\nthis logical formulation we now are entitled to apply the term \u201ccause,\u201d\nin our restricted sense of the word, to every change of the medium\nwhich is followed by any sort of adaptation in regard *to itself*. Our\ndefinition stated that a \u201ccause\u201d is any one of the sum of necessary\nfactors from without that accounts either for the localisation *or* for\n*the specification* of the effect, and the definition holds very well in\nthis case. Indeed, the specification of the effect is determined *by*\nthe outside factor in every case of an adaptation *to* it, by the mere\n*fact* of its being a specific adaptation to this specific factor.\n\nWe must not forget that in this chapter we are not studying real\nindividual morphogenesis as the realisation of what has been inherited,\nbut that at present we regard morphogenesis proper as an accomplished\nfact. Morphogenesis proper has laid the general lines of organisation;\nand now adaptation during the functional life, so to speak, imposes a\nsecond kind of organisation upon the first. It is for that reason that\nthe meaning of the word \u201ccause\u201d is now becoming a little different from\nwhat it was before.\n\nIn order to study a little more in detail what has been discovered\nabout morphological adaptation in animals and plants, let us separate\nour materials into two groups, one of them embracing adaptations with\nregard to functional changes from without, the other adaptations to\nthose functional changes which come from the very nature of functioning.\nAlmost all of our previous general considerations have applied to the\nformer group, with which we shall now proceed to deal.\n\n\nADAPTATIONS TO FUNCTIONAL CHANGES FROM WITHOUT[78]\n\n[78] Compare Herbst, *Biol. Centralbl.* 15, 1895; and Detto, *Die\nTheorie der direkten Anpassung*, Jena, 1904. A full account of the\nliterature will be found in these papers.\n\nThe differences between plants grown in very dry air, very moist air,\nand water, respectively, are most distinctly seen in all the tissues\nthat assist in what is called transpiration, that is, the exchange of\nwater-vapour between the plant and the medium, but especially in the\nepidermis and the conductive fibres, both of which are much stronger\nin plants grown in the dry. Indeed, it seems from experiments that\ntranspiration is the most essential factor to which \u201cadaptation\u201d occurs\nin amphibious plants, though the changes of the mechanical conditions\naccording to the medium also seem to have some sort of structural\neffect. If plants stand very deeply in water, the conditions of\nillumination, so important for assimilation in plants, may have been\naltered, and therefore much of the structural change can be attributed\nalso to them. It is unimportant in our general question what is due to\none of these factors and what to the other. That there is a real sort\nof adaptation cannot be doubtful; and the same is true, as experimental\nobservations of the last few years have shown, with regard to the\nstructural differences between so-called sun-leaves and shade-leaves\nof plants grown in the air: it has been actually shown here that the\nfunctional life of the former goes on better in the sun, of the latter\nbetter in the shade.\n\nIt is very important to emphasise this point, as the adaptive character\nof all sorts of structural differences in plants dependent on light\nand on moisture has lately been denied, on the supposition that there\nis only a stopping of organogenesis in the case of the more simple,\na continuance in the case of the more complicated modification, but\nnothing else. Indeed, all morphological adaptation has been conceived\nas only consisting in differences dependent upon the absence or the\npresence of necessary means or causes of development, and as offering\nno problem of its own. We have gained the right position from which\nto oppose this argument, it seems to me, in our formula that all\nadaptations do relate *not* directly *to* the agents of the medium,\nbut to changes of functional states induced *by* those agents; that\nadaptations only *are* \u201cadaptations\u201d by being correctives to the\nfunctional state.\n\nThere simply *is* an \u201cadaptation\u201d of structure in *such* a sense in all\nthe cases we have mentioned. We can say neither more nor less. Granted\nthat one of the outside factors which comes into account is merely a\nnecessary \u201cmeans\u201d: then why is the histological consequence of the\npresence of the means an actual adaptation to it as far as its relation\nto functioning is concerned--why is the consequence of its absence also\nan adaptation to this absence in its relation to functioning? Why, to\ncomplete the series, is the degree of the consequence of its presence an\nadaptation to the degree of its presence?\n\nAll these relationships, which are so many facts, have been absolutely\noverlooked by those who have been pleased to deny morphological\nadaptation to functional changes from without.\n\nTo do full justice to them we may speak of \u201cprimary\u201d regulative\nadaptations in all the cases mentioned above, applying the word\n\u201cprimary,\u201d just as was done with regard to restitutions, to the fact\nthat there is some sort of regulation *in* the normal connection of\nprocesses. We reserve the title of \u201csecondary adaptations\u201d for cases\nsuch as those described, for instance, by V\u00f6chting,[79] where not\nmerely one and the same tissue originates adaptively with regard to the\ndegree of its normal functioning, but where a profound disturbance\nof all functioning connections, due to the removal of portions of the\norganisation, is followed by histological changes at absolutely abnormal\nlocalities; that is, where a real change of the *kind* of functioning\nis the consequence of the adaptation. It, of course, will be found very\ndifficult to discriminate such phenomena from real restitutions, though\nlogically there exists a very sharp line between them.\n\n[79] V\u00f6chting (*Jahrb. wiss. Bot.* 34, 1899) forced the bulbs of\nplants to become parts of the stem, and parts of the stem to form\nbulbs; in both cases the most characteristic changes in histology\ncould be observed, being in part adaptations, but in part restitutions\nof the proper type. (See also my *Organische Regulationen*, 1901, p.\n84.) A true and simple instance of a \u201csecondary adaptation\u201d seems to\nbe furnished in a case described by Boirivant. In *Robinia* all the\nleaflets of a leaf-stalk were cut off: the leaf-stalk itself then\nchanged its structure in order to assist assimilation, and also formed\nreal stomata.\n\nA few more concrete instances may now close this account of adaptation\nto functional changes coming from without. Though almost all the\nadaptive characters in the aquatic forms of amphibious plants represent\na less complicated state of organisation than the corresponding\nstructures in their terrestrial forms, and therefore have wrongly\nbeen regarded as simply due to a stopping of morphogenesis for want\nof necessary means, yet there are a few of them that are positive\ncomplications in comparison with the land-forms: the so-called\na\u00ebrenchyme, especially well developed in the water-form of *Jussiaea*\nis such an instance. This tissue stands in the direct service of\nrespiration, which is more difficult to be accomplished under water than\nordinarily, and represents a true adaptation to the altered function.\n\nAmong animals there is only one well-studied instance of our first type\nof adaptive morphological characters. *Salamandra atra*, the black\nsalamander, a species which only inhabits regions at least two thousand\nfeet above sea-level, does not bring forth its young until metamorphosis\nhas taken place. The larvae, however, may be removed from the mother\u2019s\nbody at an earlier stage and forced to complete their development in\nwater. Under these circumstances, as was shown in an excellent memoir\nby Kammerer,[80] they will change the whole histological type of their\ngills and skin in order to meet the new functional conditions. The\nchange of the conditions of functioning is very severe here, for whereas\nthe gills had served for nutrition and respiration in the uterus--by\na process of endosmosis--they now serve for respiration only, and, of\ncourse, are surrounded by quite an abnormal chemical medium.\n\n[80] *Arch. Entw. Mech.* 17, 1904.\n\n\nTRUE FUNCTIONAL ADAPTATION[81]\n\n[81] Roux, *Gesammelte Abhandlungen*, vol. i. 1895; in particular, *Der\nKampf der Teile im Organismus*, Leipzig, 1881.\n\nBut all other cases of morphological adaptation among animals, and\nseveral in the vegetable kingdom too, belong to our second group of\nthese phenomena, which in our analytical discussion we have called\nadaptations to functional changes that result from the very nature\nof functioning, and which we shall now call by their ordinary name,\n\u201cfunctional adaptation.\u201d\n\nIt was Roux who first saw the importance of this kind of organic\nregulation and thought it well to give it a distinguishing name. *By\nfunctioning the organisation of organic tissues becomes better adapted\nfor functioning.* These words describe better than any others what\nhappens. It is well known that the muscles get stronger and stronger the\nmore they are used, and that the same holds for glands, for connective\ntissue, etc. But in these cases only quantitative changes come into\naccount. We meet with functional adaptations of a much more complicated\nand important kind, when for instance, as shown by Bab\u00e1k,[82] the\nintestine of tadpoles changes enormously in length and thickness\naccording as they receive animal or vegetable food, being nearly twice\nas long in the second case. Besides this the so-called mechanical\nadaptations are of the greatest interest.\n\n[82] *Arch. Entw. Mech.* 21, 1906. By a very detailed comparative study\nBab\u00e1k was able to prove that it is the plant proteids to which the\neffect of vegetable food is chiefly due; thus we have an adaptation\nto digestibility. Mechanical circumstances are only of secondary\nimportance. (See also Yung.)\n\nIt has long been known, especially from the discoveries of Schwendener,\nJulius Wolff, and Roux, that all tissues whose function it is to resist\nmechanical pressure or mechanical tension possess a minute histological\nstructure specially suitable to their requirements. This is most\nmarkedly exhibited in the stem of plants, in the tail of the dolphin, in\nthe arrangements of the lime lamellae in all bones of vertebrates. All\nthese structures, indeed, are such as an engineer would have made them\nwho knew the sort of mechanical conditions they would be called upon to\nencounter. Of course all these sorts of mechanically adapted structures\nare far from being \u201cmechanically explained,\u201d as the verbal expression\nmight perhaps be taken to indicate, and as indeed has sometimes been the\nopinion of uncritical authors. The structures exist *for* mechanics,\nnot *by* it. And, on the other hand, all these structures, which we\nhave called mechanically \u201cadapted\u201d ones, are far from being mechanical\n\u201cadaptations,\u201d in our meaning of the word, simply because they are\n\u201cadapted.\u201d Many of them indeed exist previous to any functioning, they\nare for the most part truly inherited, if for once we may make use of\nthat ambiguous word.\n\nBut, the merely descriptive facts of mechanical adaptedness having been\nascertained, there have now been discovered real mechanical processes\nof adaptations also. They occur among the statical tissues of plants,\nthough not in that very high degree which sometimes has been assumed\nto exist; they also occur in a very high perfection in the connective\ntissue, in the muscles and in the bone tissue of vertebrates. Here\nindeed it has proved possible to change the specific structure of the\ntissue by changing the mechanical conditions which were to be withstood,\nand it is in cases of healing of broken bones that these phenomena have\nacquired a very great importance, both theoretically and practically:\nthe new joints also, which may arise by force of circumstances,\ncorrespond mechanically to their newly created mechanical function.\n\nSo far a short review of the facts of \u201cfunctionelle Anpassung.\u201d They\nseem to prove that there does exist a morphological adaptation to\nfunctional changes which result from the very nature of functioning. In\nfact, the actual state of all functioning tissue, the intensity of its\nstate of existence, if you care to say so, may be said to be due to the\nfunctioning itself: the so-called atrophy by inactivity being only one\nextreme of a very long line of correspondences.[83]\n\n[83] Atrophy of muscles by inactivity is not to be confused with atrophy\nby cutting the motor nerve; the latter is very much more complete.\n\nWe now, of course, have to ask ourselves if any more intimate analysis\nof these facts is possible, and indeed we easily discover that here\nalso, as in the first of our groups of morphological adaptations,\nthere are always single definite agents of the medium, which might be\ncalled \u201ccauses\u201d or \u201cmeans\u201d of the adaptive effects, the word \u201cmedium\u201d\nbeing taken as embracing everything that is external to the reacting\ncells. But of course also here the demonstration of single formative\nagents does not detract in the least from the adaptive character of\nthe reaction itself. So we may say, perhaps, that localised pressure\nis the formative stimulus for the secretion of skeleton substance at a\nparticular point of the bone tissue, or of the fibres of the connective\ntissue; the merely quantitative adaptations of muscles might even\nallow of a still more simple explanation.[84] But adaptations remain\nadaptations in spite of that; even if they only deserve the name of\n\u201cprimary\u201d regulations.\n\n[84] Loeb has advocated the view that the \u201cadaptive\u201d growth of working\nmuscles is simply due to the presence of a greater number of molecules\nin their protoplasm, muscular activity being generated by a process of\nchemical decomposition.\n\n\nTHEORETICAL CONCLUSIONS\n\nWe have stated in the analytical introduction to this chapter and\nelsewhere, that functional changes, which lead to morphological\nadaptations of both of our groups, may arise not only from changes of\nfactors in the medium, but also from a removal of parts. As such removal\nis generally followed by restitution also, it is clear that restitutions\nand adaptations very often may go hand in hand, as is most strikingly\nshown in a fine series of experiments carried out by V\u00f6chting, which we\nhave already alluded to. Here again I should like to lay the greatest\nstress upon the fact that, in spite of such actual connections,\nrestitutions and adaptations always have been separated from another\ntheoretically, and that the forms are never to be resolved into sums\nof the latter. Such a view has been advocated by some recent authors,\nespecially by Klebs, Holmes, and Child:[85] it is refuted I think by the\nsimple fact that the first phase of every process of restitution, be it\nregeneration proper or be it a sort of harmonious differentiation, goes\non without functioning at all, and only *for* future functioning.[86]\n\n[85] What has been really *proved* to exist by the very careful studies\ncarried out by Child, is only certain cases of functional adaptation\nto mechanical conditions of the strictest kind, and relating to the\ngeneral mobility only, but nothing more; such adaptations can be said to\naccompany restitution. See, for instance, *Journ. exp. Zool.* 3, 1906,\nwhere Child has given a summary of his theory.\n\n[86] Even in V\u00f6chting\u2019s experiments (see page 174, note 1), in which\nadaptations are mixed with true restitutions in the closest possible\nmanner, a few phenomena of the latter type could most clearly be\nseparated. The stimulus which called them forth must have been one of\nthe hypothetic sort alluded to in a former chapter (see page 113). The\nbest instances of true restitutions were offered in those cases, where,\nafter the removal of all the bulbs, typical starch-storing cells were\nformed without the presence of any starch.\n\nAnd there has been advocated still another view in order to amplify\nthe sphere of adaptation: all individual morphogenesis, not only\nrestitution, is adaptation, it has been said. In its strictest form\nsuch an opinion of course would simply be nonsense: even specific\nadaptive structures, such as those of bones, we have seen to originate\nin ontogeny previous to all specific functions, though for the help\nof them, to say nothing of the processes of the mere outlining of\norganisation during cleavage and gastrulation. But they are \u201cinherited\u201d\nadaptations, it has been answered to such objections. To this remark we\nshall reply in another chapter. It is enough to state at present that\nthere *is* a certain kind of, so to speak, architectonic morphogenesis,\nboth typical and restitutive, previous to specific functioning\naltogether.\n\nIf now we try to resume the most general results from the whole field\nof morphological adaptations, with the special purpose of obtaining new\nmaterial for our further philosophical analysis, we have reluctantly to\nconfess that, at present at least, it does not seem possible to gather\nany new real proof of life-autonomy, of \u201cvitalism,\u201d from these facts,\nthough of course also no proof against it.\n\nWe have stated that there is in every case of both our types of\nadaptive events a correspondence between the degree of the factor\nto which adaptation occurs, and the degree of the adaptive effect.\nWe here may speak of an *answering* between cause and effect with\nregard to adaptation, and so perhaps it may seem as if the concept of\nan \u201canswering reaction\u201d (\u201cAntwortsreaktion\u201d), which was introduced\ninto science by Goltz[87] and which is to play a great part in our\ndiscussions of next summer, may come into account: but in our present\ncases \u201canswering\u201d only exists between a simple cause and a simple effect\nand relates almost only to quantity and locality. There is therefore\nlacking the most important feature, which, as will be seen, would have\nmade the new concept of value.\n\n[87] *Beitr\u00e4ge zur Lehre von den Functionen der Nervencentren des\nFrosches*, Berlin, 1869.\n\nWe only, I believe, can state the fact that there *are* relations\nbetween morphogenetic causes and effects which *are* adaptations, that\nfunctional disturbances or changes are followed by single histogenetic\nreactions from the organism, which are compensations of its disturbed or\nchanged functional state. We are speaking of facts here, of very strange\nones indeed. But I feel unable to formulate a real proof against all\nsorts of mechanism out of these facts: there *might* be a machine, to\nwhich all is due in a pre-established way. Of course we should hardly\nregard such a machine as very probable, after we have seen that it\n*cannot* exist in other fields of morphogenesis. But we are searching\nfor a new and independent proof; and that is indeed not to be found\nhere.[88]\n\n[88] The \u201csecondary adaptations\u201d observed by V\u00f6chting are too\ncomplicated and too much mingled with restitutions to allow any definite\nanalysis of the fact of the \u201csecondary adaptation\u201d as such.\n\nAt present it must be taken as one of the fundamental *facts* of the\norganogenetic harmony, that the cells of functioning tissues do possess\nthe faculty of reacting to factors which have changed the state of\nfunctioning, in a way which normalises this state histologically. And\nit is a fact also that even cells, which are not yet functioning but\nare in the so-called embryonic or indifferent condition contributing to\nthe physiological completion of the tissue, react to factors embracing\nnew functional conditions of the whole in a manner which leads to an\nadaptation of that whole to those conditions.\n\nThis is a very important point in almost all morphological adaptation,\nwhether corresponding to functional changes from without or resulting\nfrom the very nature of functioning. In fact, such cells as have already\nfinished their histogenesis are, as a rule, only capable of changing\ntheir size adaptively, but are not able to divide into daughter-cells\nor to change their histological qualities fundamentally; in technical\nterms, they can only assist \u201chypertrophy\u201d but not \u201chyperplasia.\u201d Any\nadaptive change of a tissue therefore, that implies an increase in the\nnumber of cellular elements or a real process of histogenesis, has to\nstart from \u201cindifferent\u201d cells, that is to say, cells that are *not yet*\nfunctioning in the form that is typical of the tissue in question; and,\nstrange to say, these \u201cembryonic\u201d cells--*i.e.* the \u201ccambium\u201d in higher\nplants and many kinds of cells in animals--*can* do what the functional\nstate requires. It is to be hoped that future investigations will lay a\ngreater stress upon this very important feature of all adaptation.\n\n\n2. PHYSIOLOGICAL ADAPTATION[89]\n\n[89] General literature: Fr\u00f6hlich, *Das nat\u00fcrliche\nZweckm\u00fcssigkeitsprincip in seiner Bedeutung f\u00fcr Krankheit und Heilung*,\n1894. Driesch, *Die organischen Regulationen*, 1901. A. Tschermak, \u201cDas\nAnpassungsproblem in der Physiologie der Gegenwart,\u201d in a collection\nof papers in honour of J. P. Pawlow, St. Petersburg, 1904. Bieganski,\n\u201cUeber die Zweckm\u00e4ssigkeit in den pathologischen Erscheinungen,\u201d *Annal.\nd. Naturphil.* 5, 1906. Among the general text-books of physiology those\nby Pfeffer (*Pflanzenphysiologie*, 1897-1904) and von Bunge (*Lehrbuch\nd. Phys. d. Menschen*, 1901) are the fullest on the subject of\n\u201cregulations.\u201d See also different papers on general pathology by Ribbert.\n\nIt is but a step from morphological adaptations to adaptations in\nphysiology proper. The only difference between regulations of the\nfirst type and those which occur in mere functioning is, that the\nresulting products of the regulation are of definite shape and therefore\ndistinctly visible in the first case, while they are not distinctly\nvisible as formed materials but are merely marked by changes in chemical\nor physical composition in the latter.\n\nMetabolism, it must never be forgotten, is the general scheme within\nwhich all the processes of life in a given living organism go on; but\nmetabolism means nothing else, at least if we use the word in its\ndescriptive and unpretentious meaning, than change in the physical\nor chemical characteristics of the single constituents of that\norganism. In saying this, we affirm nothing about the physical or\nchemical nature of the actual processes leading to those physical or\nchemical characteristics, and by no means are these \u201cprocesses\u201d *a\npriori* regarded as being physical or chemical *themselves*: indeed,\nwe have learned that in one large field, in the differentiation of\nour harmonious systems they certainly are not. Now, if the metabolism\ndoes not end in any change of visible form, then true physiological\nprocesses, or more particularly physiological regulations, are going on\nbefore us. But we are dealing with morphogenetic events or regulations,\nif the result of metabolism is marked by any change in the constituents\nof form. This however may depend on rather secondary differences as to\nthe nature of regulation itself, and any kind of metabolism may really\nbe of the regulatory type, whether we actually see its result as a\nconstituent of form, *e.g.* owing to the production of some insoluble\ncompound, or whether we do not.\n\nI do not mean to say that these are the only differences between mere\nphysiological activities or regulations and organogenesis proper, as an\noriginating of typical form-combination; but if we regard, as we do in\nthis chapter, the given organisation of a living being as a substratum\nof its functional life, morphological and physiological adaptations are\nindeed of almost the same logical order.\n\nWe had best therefore begin our discussions with a recapitulation of\nour problem. We are studying adaptations in functioning--that means we\nwant to know how the organism behaves with regard to any change which\nmay take place in its functional state. We apply the term regulation,\nor in particular adaptation, to any kind of reaction on the part of the\norganism which re-establishes the normal state of functioning, and we\nnow want to learn to what degree such adaptations exist in the field of\nphysiology.\n\n\nSPECIFIC ADAPTEDNESS *NOT* \u201cADAPTATION\u201d\n\nIt is important to keep well in mind our strictly formulated theme, as\nby doing so we shall be able to exclude at once from our materials a\nlarge group of phenomena which occasionally have been called regulations\nby physiological authors, but which, in fact, are not of the adaptation\ntype and therefore cannot be said to afford those problems which\npossibly might have been expected. Typical peculiarities in functional\nlife cannot be called \u201cregulations\u201d for this very reason. If, for\ninstance, the organism selects specific amounts of specific kinds of\norganic food or of salts out of the combinations of salts or organic\nfood normally offered to it in the medium, as indeed is most typically\nshown for instance by the roots of plants, there cannot be said to occur\na \u201cregulation\u201d or \u201cadaptation\u201d with regard to the permeability of the\ncell, nor is it strictly a case of \u201cregulation,\u201d if so-called selective\nqualities are discovered in the processes of secretion, say of the\nepithelium of the kidney.\n\nAll these facts are typical and specific peculiarities in functioning\nwhich are duly to be expected, where a very typical and specific\norganisation of the most elaborated kind exists. Indeed, after studying\nsuch an organisation we must not be astonished that functions in\norganisms follow lines which certainly they would not have taken without\nit. Take the fact which is quoted very often, that the migration of\ncompounds or of ions in the organisms can happen quite contrary to all\nthe laws of osmosis, from the less concentrated to the more concentrated\nside of a so-called \u201cmembrane.\u201d There *is* no simple \u201cmembrane\u201d in the\norganism, but a complicated organisation of an almost unknown character\ntakes its place, and nothing, indeed, is against the assumption that\nthis organisation may include factors which actually drive ions or\ncompounds to the side of higher concentration, which indeed drive them\nby \u201cdoing work,\u201d if we like to speak in terms of energy; and these\nfactors included in organisation may very well be of a true physical or\nchemical nature.[90]\n\n[90] According to investigations of the last two years, the physics of\ncolloids seems to play as important a part in physiology as osmosis\ndoes; we here meet \u201cmeans\u201d of functioning just as we have already had\n\u201cmeans\u201d of organogenesis.\n\nI lay great stress upon these statements, as I should like to be as\ncareful as possible in the admission of anything like a \u201cproof\u201d of\nvitalism. It was want of scientific criticism and rigid logic that\ndiscredited the old vitalism; we must render our work as difficult as\npossible to ourselves, we must hold the so-called \u201cmachine theory\u201d of\nlife as long as possible, we must hold it until we are really forced to\ngive it up.\n\nIn a more general form we now can sum up our discussion by saying: There\nnever are adaptations in physiology, requiring any special analysis,\nwhere there are only complications or even apparent deviations from the\npurely physico-chemical type of events which are, so to say, statical,\n*i.e.* fixed in quantity or quality, however peculiar or typically\ncomplicated they may be; all such peculiarities indeed, may properly\nbe called \u201cadapted,\u201d that is to say, very well fitted to perform a\nspecific part in the service of normal general functioning, and they\nare \u201cadapted\u201d to their part by virtue of a certain \u201cadaptedness\u201d of the\norganisation; but they are not \u201cadaptations\u201d in any sense of the word.\n\n\nPRIMARY AND SECONDARY ADAPTATIONS IN PHYSIOLOGY\n\nWe approach the subject of true adaptations, that is, of adapting\nprocesses, as soon as any kind of variation in functioning occurs which\ncorresponds to a variation of any factor of the medium in the widest\nsense. But even here our work is by no means done by simply showing\nsuch a correspondence of outer and inner variations. We know very well\nalready, from our former studies, that now we are faced by a further\nproblem, that we are faced by the question whether we have to deal with\nsimple primary kinds of adaptations or with the far more important\nsecondary ones.\n\nAs the discrimination between primary and secondary regulations proves\nindeed to be of first-rate importance, you will allow me, I hope, to\nsummarise our chief analytical statements regarding them in a most\ngeneral form. We call primary regulatory any kind of morphogenetic or\nfunctional performance, which, by its very intimate nature, always\nserves to keep the whole of organisation or of functions in its normal\nstate. We call secondary regulations all features in the whole of\nmorphogenesis or of functioning which serve to re-establish the normal\nstate after disturbances along lines which are outside the realm of\nso-called normality. This analytical discrimination will help us very\nmuch to a proper understanding of physiology. But before we turn to\napply our definitions to actual facts, another preliminary problem has\nto be solved.\n\n\nON CERTAIN PRE-REQUISITES OF ADAPTATIONS IN GENERAL\n\nWe are thinking of the general and important question, what types of\nadaptations may be expected in the field of physiology and whether\nthere may be certain classes of regulatory events which possibly might\nbe expected to occur in the organism on *a priori* grounds, but which,\nnevertheless, are to be regarded as impossible after a more intimate\nanalysis of its nature, even at the very beginning? Or, in other words,\nto what kinds of changes of the medium will an organism be found able or\nunable to adapt itself?\n\nWe know that the *state of functioning* must be altered in order to call\nforth any sort of adaptation at all. Now, there can be no doubt that *a\npriori* it would seem to be very useful for the organism, if it never\nwould let enter into its blood, lymph, etc., be it through the skin or\nthrough the intestine, any chemical compound that would prove to be\na poison afterwards. In fact, a man, judging on the principle of the\ngeneral usefulness of all the phenomena of the living, might suppose\nthat there would exist a sort of adaptation against all poisons to the\nextent that they would never be allowed to enter the real interior of\nthe body. We know that such reasoning would be incorrect. But we also\ncan understand, I suppose, that an *a priori* analysis of a more careful\nkind would have reasoned differently. How could the functional state\nof the organism be changed, and how, therefore, could adaptation be\ncalled forth by any factor of the medium which had not yet entered the\norganism, but was only about to enter it? Not at all therefore is such\na regulation to be expected as we have sketched; if there is to be any\nadaptation to poisons, it only can occur after the poison has really\nacted in some way, and in this case we shall indeed find regulations.\n\nYou may perhaps regard this discussion as a little too academical\nand hair-splitting, but here again it was for the sake of ensuring a\nperfectly sound foundation of our chief principles that I undertook it.\nVery often, indeed, the question has been raised by the defenders of a\nmechanistic theory of life, Why then did the organisms not reject all\npoisons from the very beginning? We now may reply to that only--how\n*could* they do so? How could they \u201cknow\u201d what is a poison and what is\nnot, unless they had experienced it?--if we are allowed for a moment to\nuse very anthropomorphistic language.\n\nWe repeat, therefore, that the functional conditions of the organism\nmust have been actually changed in order that an adaptation may occur.\nNothing is more essential to a clear understanding of our problems than\nto keep fully in mind the exact sense of this definition.\n\n\nON CERTAIN GROUPS OF PRIMARY PHYSIOLOGICAL ADAPTATIONS\n\n*General Remarks on Irritability.*--Turning now to more special groups\nof problems concerning physiological adaptations, let us begin with the\nprimary class of them, and let us first say a few words on a subject\nwhich occasionally has been regarded as the basis of physiological\nregulation in general. I refer to a most important fact in the general\nphysiology of irritability. Irritability of any kind is known to be\nre-established, after it has been disturbed by the process of reacting\nto the stimulus, and in certain cases, in which two different--or rather\ntwo opposite--kinds of reactions are possible on the same substratum,\nwhich increase with regard to one process whilst decreasing at the same\ntime with regard to the other. The irritability of the muscle or of the\nleaves of *Mimosa* is a very good instance of the first case, whilst the\nsecond more complicated one cannot be illustrated better than by what\nall experience has taught us about the irritability of the retina. The\nretina is more irritable by green rays and less by red ones the more\nit has been stimulated by the latter, and more sensitive to light in\ngeneral the more it has been exposed to darkness; and something very\nsimilar is true, for instance, as regards phototactic irritability in\nplants, all these phenomena being in relation to the so-called law of\nWeber.[91]\n\n[91] I only mention here that certain modern psychologists have assigned\nthe true law of Weber to the sphere of judgment and not of sensation. If\napplied to objective reactions only, in their dependence on objective\nstimuli, it, of course, becomes less ambiguous, and may, in a certain\nsense, be said to measure \u201cacclimatisation\u201d with regard to the stimulus\nin question. The mathematical analogy of the law of Weber to the most\nfundamental law of chemical dynamics seems very important.\n\nAs to \u201cacclimatisation\u201d in the more usual meaning of the word, with\nregard to a change of the general faculty of resisting certain agents\nof the medium, \u201cimmunity\u201d proper is to form a special paragraph of what\nfollows, and to \u201cacclimatisation\u201d towards different degrees of salinity\n(in algae or fishes) some special remarks will also be devoted on a\nproper occasion. There remains only \u201cacclimatisation\u201d to different\ntemperatures; but on this topic not much more than the fact is known\n(see Davenport, *Arch. f. Entw. Mech.* 2, p. 227). \u201cAcclimatisation\u201d\ndoes not allow of a sharp general definition; it may be the result of\nvery *different* kinds of adaptations in our sense of the word.\n\nIt seems to me that there would be little difficulty in harmonising the\nphenomenon of the inversion of irritability with the so-called principle\nof the \u201caction of masses\u201d and with the laws of certain \u201creversible\u201d\nprocesses well known in chemistry. As to the simple fact of the\nre-establishment of irritability after stimulation has occurred, or,\nin certain other cases, the fact that in spite of permanent stimulation\nirritability seems to exist permanently also, physical analogies or even\nexplanations might very well be found.[92]\n\n[92] I should think that the problem of the re-establishment of\nirritability, in principle at least, arises even when there is not a\ntrace of so-called \u201cfatigue\u201d or of a \u201crefractory period.\u201d The process\nof restoring may be so rapid as not to be noticeable, nevertheless some\nsort of restoring is to be postulated. We may say the \u201cirritability\u201d of\nan elastic ball is re-established by its elasticity. A certain analogy\nto this case may perhaps be found in the muscle. But the irritability\nof nerves with respect to nervous conduction, and of glands with\nrespect to secretion, or of the articulations of *Mimosa* may be well\nunderstood, hypothetically at least, if we assume that the ordinary\ncourse of metabolic events is apt in itself to lead to a certain state\nor condition of the organs in question upon which their irritability\nis based. Certain general conditions of functioning, as for instance\nthe presence of oxygen for the contraction of the muscle, would better\nbe looked upon as necessary \u201cmeans\u201d of functioning than as being part\nof irritability as such. \u201cFatigue,\u201d of course, may also be due to\nthe absence of such \u201cmeans\u201d or to abnormal conditions originated by\nfunctioning itself.\n\nIf now we ask whether there is anything like an adaptation appearing in\nthe general characteristics of irritation and irritability, it seems to\nme that we may answer the question in an affirmative manner, as far as\nprimary regulation comes into account. We, certainly, have not studied\nany abnormal regulatory lines of general functioning, we only have\nstudied general functioning itself; but, indeed, there was a certain\nsort of regulation *in* functioning. Of course, by showing that one\nof the most general features of all functioning is primary-regulatory\nin itself, we do not deny the possibility of many specific functions\nin which real secondary regulations actually do exist. Nothing indeed\nis asserted about the *specific* character of functioning in its\ndifferent types, by proving that one of the *general* features of *all*\nfunctioning may comparatively easily be understood. It seems to me that\nthis important logical point has not always received the attention it\ndeserved.\n\n*The Regulation of Heat Production.*[93]--Having finished our\nintroductory remarks we now turn to the proper study of special\nphysiological functioning with regard to its adaptive side, and begin\nwith the most simple cases.\n\n[93] Rubner, *Die Gesetze des Energieverbrauches bei der Ern\u00e4hrung*,\nLeipzig u. Wein, 1902.\n\nThe so-called \u201cregulation of heat\u201d in warm-blooded vertebrates is an\ninstance of a special function which can be said to be regulatory in\nitself. There exists a normal blood heat for each species, which is\nmaintained no matter whether the temperature of the medium rise or fall.\nIt might seem at first as if in this case there were a little more\nof an adaptive regulation than only its well-known primary type; no\nreversion, one might say, of the direction of one and the same process\noccurs in the regulation of heat production, but one kind of process\nis called into action if it is necessary to raise the temperature, and\nanother whenever it is necessary to lower it. Even in the dilatation\nand constriction of capillary vessels there are different nerves\nserving for each operation respectively, and far more important are the\nincreasing of transpiration for cooling, the increasing of combustion\nfor heating--two radically different processes. But, nevertheless, there\nis a certain unity in these processes, in so far as a specific locality\nof the brain has been proved to be the \u201ccentre\u201d of them all; it is to\nthis centre of course that the analysis of heat production considered as\na kind of regulation or adaptation must be directed. Such an ultimate\nanalysis, it seems to me, would have to classify heat regulation under\nthe primary type of adaptations in physiology without any restriction.\nThe centre acts in one sense or in the other, if stimulated by any\ntemperature beyond a very limited range, and it is in the action of the\ncentre that the \u201cregulation\u201d of heat consists.[94]\n\n[94] The phenomenon of fever we leave out of account here; it is\nregarded by some as regulation, by others as a disturbance of heat\nregulation. Of course, if the first view should ever prove to be the\nright one, fever might be classified among the real regulations of the\nsecondary type.\n\n*Primary Regulations in the Transport of Materials and Certain Phenomena\nof Osmotic Pressure.*--Very similar phenomena of regulation are present\nin many processes concerned in the whole of metabolism. Let us consider\nfor a moment the migration of materials in plants. Whenever any compound\nis used at a certain place, a permanent afflux of this compound to\nthat place sets in from all possible directions. No doubt this is a\n\u201cregulation,\u201d but it is also the function itself, and besides that,\na very simple function based almost entirely on well-known laws of\nphysical chemistry. And in other cases, as in the ascent of water to\nthe highest tops of our trees, which purely physical forces are said to\nbe insufficient to explain, we can appeal to the unknown organisation\nof many cells, and there is nothing to prevent our attributing to these\ncells certain functions which are, if you like to say so, regulatory\nin themselves. Among other facts of so-called regulations there is the\nstopping of metabolic processes by an accumulation of their products:\nas, for instance, the transformation of starch into sugar is stopped,\nif the sugar is not carried away. Of course that is a regulation, but\nit again is an intrinsic one, and it is one of the characteristics of\nreversible chemical processes to be stopped in that way. I know very\nwell that in this particular case a certain complication is added by\nthe fact that it is a so-called ferment, the diastase, which promotes\nthe transformation of starch into cane-sugar, and that this ferment is\nactively produced by the organism: but even its production would not\nprove that any real kind of secondary regulation exists here, if nothing\nmore were known about such an active production than this single case.\n\nIn a special series of experiments almost all carried out in Wilhelm\nPfeffer\u2019s botanical laboratory at Leipzig, an attempt has been made\nto discover in what manner the cells of plants are able to withstand\nvery high abnormalities of the osmotic pressure of the medium--that is\nto say, very great changes in the amount of its salinity. That many,\nparticularly the lower plants, are able to stand such changes had been\nascertained already by the careful examinations of Eschenhagen; but\nrecent years have given us a more profound insight into what happens.\nVon Mayenburg[95] has found that sundry of the species of *Aspergillus*,\nthe common mould, are able to live in very highly concentrated solutions\nof several salts (KNO_3 and Na_2SO_4). They were found to regulate\ntheir osmotic pressure not by taking in the salts themselves, but by\nraising the osmotic pressure of their own cell sap, producing a certain\namount of osmotically active substances, probably carbohydrates. If\nin this case it were possible to assume that the osmotic pressure of\nthe medium were the real stimulus for the production of the osmotic\nsubstances in the cell, stimulus and production both corresponding\nin their degree, we should be entitled to speak of a primary though\nphysiological[96] regulation only; and it seems to me that despite the\ndiscoveries of Nathansohn that certain algae and cells of higher plants\nare able to change the permeability of their surfaces in a way which\nregulates the distribution of single salts or ions in the sap of their\ncells without any regard to pure osmotic equilibrium, such a simple\nexplanation might be possible.[97]\n\n[95] *Jahrb. wiss. Bot.* 36, 1901.\n\n[96] Carbohydrates cannot be ionised, and therefore there is no doubt\nthat in von Mayenburg\u2019s experiments the organism itself is actively\nat work. As to compounds liable to ionisation, it has been noticed by\nMaillard that a certain regulatory character is contained simply in the\nphysical fact that the degree of ionisation changes with concentration:\ndecrease of concentration for instance would be followed by an increase\nof ionisation, and so the osmotic pressure may be preserved (*C. rend.\nSoc. Biol.* 53, 1901, p. 880).\n\n[97] In the different experiments of Nathansohn (*Jahrb. wiss. Bot.*\n38, 1902, and 39, 1903) the salinity of the medium was changed in such\na way that there was in each case either an abnormal increase or an\nabnormal decrease in the concentration of one single ion necessary\nfor metabolism. The cell was found to stand these abnormal changes in\nsuch a way that in the case of the increase of the concentration of\nthe medium it did not allow more than a certain amount of the ion in\nquestion to come in, and that in the case of the decrease it did not\nallow more than a certain quantity of the ion to go out. It thus seems\nas if the permeability of the surface were adjusted to a certain minimum\nand to a certain maximum of every single ion or salt, the permeability\nbeing stopped from within to without, whenever the minimum, and from\nwithout to within, whenever the maximum is reached in the cell sap; both\nirrespective of proper physical osmotic equilibrium (\u201cPhysiologisches\nGleichgewicht\u201d). Thus, in fact, there only would be a case of primary\nregulation, nothing more. It would all appear rather similar to what\noccurs in the kidney. Of course we do not assert that our explanation is\nright, but it is possible and is at the same time the most simple, and\nit is our general practice always to prefer the most simple hypotheses.\n\nThere are many regulation phenomena connected with osmotic pressure\nand permeability in animal physiology also, though at present they are\nnot worked out as fully as possible. The works of Fr\u00e9d\u00e9ricq, J. Loeb,\nOverton and Sumner[98] would have to be taken into account by any\none who wished to enter more deeply into these problems. We can only\nmention here that permeability to water itself also plays its part, and\nthat, according to Overton\u2019s experiments, it is a kind of solubility\nof the media in the very substance of the cell surface on which all\npermeability and its regulation depend.\n\n[98] Many fishes are able to withstand great changes in the osmotic\npressure of sea-water; the osmotic pressure of their body fluids, though\nnever in a real physical equilibrium with the pressure of the medium,\nnevertheless may vary whenever the abnormal conditions of the latter\nexceed certain limits.\n\n*Chromatic Regulations in Algae.*--The phenomena of osmotic pressure and\nits regulation may be said to be the preliminaries of metabolism proper,\nconditions necessary for it to take place. Now there is another branch\nof such preliminaries to metabolism, in which the most interesting\nregulation phenomena have been lately discovered. It is well known that\nwhat is called assimilation in plants, that is, the formation of organic\ncompounds out of carbon dioxide (CO_2) and water, occurs only in\nthe light by means of certain pigments. This pigment is in all higher\nplants and in many others the green chlorophyll, but it may be different\nin certain species of algae, and can generally be said[99] to be of\nthe colour complementary to the colour of those rays which especially\nare to be absorbed and to be used for assimilation. But here we have\n\u201cadaptedness,\u201d not adaptation. It was in some species of primitive\nalgae, the *Oscillariae*, that Gaidukow[100] found a very interesting\ninstance of an active regulation in the formation of pigments. These\nalgae always assume a colour which corresponds to the accidental colour\nof the rays of the medium and is complementary to it; they become green\nin red light, yellow in blue light, and so on--that is, they always\nactively take that sort of colouring which is the most suitable to\nthe actual case.[101] There indeed occurs a sort of complementary\nphotography in these algae; but, though adaptive, it could hardly be\nsaid to exceed the limits of \u201cprimary phenomena.\u201d\n\n[99] See Stahl, *Naturw. Wochenschrift*, N. F. 5, 1906, No. 19.\n\n[100] *Arch. Anat. Phys.*, Phys. Abt. Suppl., 1902.\n\n[101] The adaptive phenomena discovered by Gaidukow depend upon a real\nalteration in the formation of pigments. In the (primary) chromatic\nadaptation of pupae of Lepidoptera with respect to the colour of\nthe ground they live upon, we only have the variable effects of\npre-established chromatophores (Poulton, *Phil. Trans. London*, 178 B,\n1888; Merrifield, *Trans. Ent. Soc. London*, 1898). The same holds for\nchromatic adaptations in crabs (Gamble and Keeble, *Quart. Journ. Micr.\nSci.* 43, 1900; Minkiewicz, *Arch. Zool. exp. et g\u00e9n.* s\u00e9r. 4, 7, notes,\n1907).\n\n*Metabolic Regulations.*--And now we enter the field of regulations in\nmetabolism itself. There are two kinds of outside factors of fundamental\nimportance for all metabolic processes: food is one, and oxygen is the\nother. And metabolism as a whole is of two different aspects also:\nit both serves for assimilation proper--that is, building up--and it\nsupplies the energy for driving the functional machine. It is clear\nthat food alone--together of course with the assimilating means of the\norganism, can account for the first type of metabolism, while both food\nand oxygen, or some sort of substitute for the latter, as in certain\nbacteria, supply functional energy. Of course we are not entitled to say\nthat the importance of so-called oxidation or respiration is exhausted\nby its energetic r\u00f4le: it certainly is not, for if it were, the organism\nwould only be stopped in its functions if deprived of oxygen but\nwould not die. It seems that certain substances always arise in the\nmetabolism, in the processes of decomposition, which have to be burnt up\nin order not to become poisonous. But we shall return to the phenomena\nof organic oxidation in another chapter of the book, and shall deal with\nthem from a more general point of view.[102]\n\n[102] The theory of oxidation we have shortly sketched here was\ndeveloped in chapter B. 5, of my *Organische Regulationen*. Recent\ndiscoveries of Winterstein\u2019s (*Zeitschr. allg. Physiol.* 6, 1907)\nhave given the strongest support to my hypothetic statements, and, in\nfact, can be said to have brought the doctrine of organic oxidation\nto a critical point. There can be no doubt that oxygen not only plays\nthe \u201cantipoisonous\u201d r\u00f4le I had assigned to it, but that it is not\neven of such great importance for the supply of functional energy as\nformer times had assumed. No doubt it serves to drive the functional\nmachine, but decomposition of certain chemical constituents of the\norganism serves this purpose even more. The latter does so in the most\nfundamental and original manner, so to speak, whilst oxidation only\nburns up its products. Almost all elemental functions, in nerve-tissue\nat least, go on very well in the absence of oxygen, provided that\ncertain \u201cpoisonous\u201d substances, resulting from this ana\u00ebrobic\nmetabolism, are constantly removed. In normal conditions that is\ndone by oxygen, and in doing so oxygen certainly assists the supply\nof energy, but it does not furnish the whole of it. The difference\nbetween so-called \u201ca\u00ebrobic\u201d and \u201cana\u00ebrobic\u201d life almost completely\ndisappears under such a view, and many so-called \u201cregulations,\u201d of\ncourse, disappear at the same time; there is no more \u201cintramolecular\nrespiration.\u201d\n\nLet us now try to take a short survey of all the regulations discovered\nrelating to the substitution of one kind of food for another. We have\nsaid that food serves in the first place as building material, in the\nsecond place as fuel. It only deserves brief mention that, as all recent\ninvestigations have shown, fats, carbohydrates, and albumen are equally\nwell able to serve as fuel.[103]\n\n[103] But nevertheless albumen is not to be replaced altogether in\nvertebrates by fat or carbohydrate; it probably serves some special\nfunction besides combustion, even in the adult.\n\nIt is in the state of fasting, *i.e.* in the case of a real absence of\n*all* nourishing materials, that the organism has proved to be capable\nof regulations of the most marked nature, with regard to the combustion\nof its own materials. Respiration, we know, must go on if death is to\nbe avoided, and now indeed it has been found that this process attacks\nthe different tissues of the organism subjected to fasting in such an\norder that, after the combustion of the reserves, the most unimportant\ntissues with regard to life in general are destroyed first, the most\nimportant ones last. Thus in vertebrates the nerve cells and the heart\nare preserved as long as possible; in infusoria it is the nucleus; in\nflatworms, as the very careful studies of E. Schultz[104] have lately\nshown, it is the nerve cells and the sexual cells which longest resist\ndestruction, whilst almost all the rest of the organisation of these\nanimals may disappear. I should not say that we can do very much with\nthese facts at present in our theoretical discussion, but they are\ncertainly witness of very astonishing adaptive powers.[105]\n\n[104] *Arch. Entw. Mech.* 18, 1904.\n\n[105] To a physiological friend of mine I owe the suggestion that it is\nthe permanently functioning tissues which stand hunger better than the\nothers, at least if the sexual cells might be regarded as capable of\na *s\u00e9cr\u00e9tion interne* in all cases. Then the adaptations in the state\nof hunger might be said to be reduced in some degree to \u201cfunctional\nadaptation.\u201d But it must remain an open question, it seems to me,\nwhether such a view may indeed hold in the face of the facts observed in\n*Planaria* and infusorians.\n\nWe now turn to study the cases of a compensation of nourishments\nserving for the real building up of the organism. Albumen, we know, is\nabsolutely indispensable for animals, even for adults, though nothing is\nknown about the purpose it serves in the latter; its place can be taken\nof course by those less complicated compounds which result from its\nfirst decomposition, effected by pepsin and trypsin, but nothing else\nwill do. The salts of sea-water, according to Herbst\u2019s experiments, may\nonly vary to a very small degree if the development of marine animals\nis to go on well; potassium may be replaced by caesium or rubidium,\nand that is all. Much the same is true of the salts necessary to\nplants. It will not surprise us very much to hear that algae can also\nbe successfully fed with the potassium salts of organic compounds, and\nhigher plants with acid amides or glucoses instead of carbonic acid, as\nthose products are normal steps in their assimilation; and it may also\nbe fairly easily understood that nitrogen can be offered in organic form\ninstead of as a nitrate.\n\nIt was in the group of fungi that really important adaptations with\nregard to the proper form-producing alimentation were first discovered,\nand these are of a very complicated kind indeed. Fungi are known to\nbe satisfied with one single organic compound instead of the group of\nthree--fat, carbohydrate and albumen--necessary for animals. Now Pfeffer\nshowed that the most different and indeed very abnormal compounds were\nable to bring his subjects to a perfect growth and morphogenesis; and,\nmoreover, he found that, if several kinds of such food were offered\ntogether, they were consumed quite indifferently as to their chemical\nconstitution, but only with regard to their nutritive value: that sort\nof food which had produced a better growth than another when both\nwere offered separately was found to save the latter from consumption\nwhenever both were offered together.\n\nHere we are faced by one of the most typical cases of regulations in\nmetabolic physiology: the organism is able to decompose compounds of\nthe most different constitution, which have never been offered to it\nbefore; but nevertheless, it must remain an open question whether real\n\u201csecondary\u201d regulation has occurred, as nothing is known in detail about\nthe single steps of metabolism in these fungi. There *might* be some\nferments equally able to destroy different classes of compounds,[106]\nand that the most nutritive compound is used up first *may* be a\nquestion of physico-chemical equilibrium.\n\n[106] In all cases where fungi of the same species are able to live on\ndifferent hosts, that is, to penetrate membranes of a different chemical\ncharacter, a similar objection as to the \u201csecondary\u201d type of such a\nregulation may be made.\n\nThat is almost all[107] that is actually known of adaptation with regard\nto the use of an abnormal food supply. Though important, it cannot be\nsaid to be very much. But could we expect very numerous regulations\nhere at all after what we laid down in a former paragraph about the\npossibilities of adaptive regulation in general? The functional state\nmust have been altered in order that such regulations may occur. Now\nthere is no doubt that this state may be really altered only if an\nabnormal food has first been taken in altogether by the cell-protoplasm\nof the body-surfaces, but never if it has only entered the cavity of the\nintestine, which, strictly speaking, is a part of the exterior medium.\nFungi indeed not only take in the abnormal food, but also know what\nto do with it, but all animals are obliged to treat first with their\nchemical secretions what happens to be present in their intestine, in\norder that it may be taken up by their living cells, and one hardly\ncan wonder that these secretions are only formed in correspondence to\na limited number of outside stimuli. In fact, as soon as we look upon\nwhat adaptive or regulatory work happens in metabolism *inside* the body\ninterior, we meet, even in animals, regulations of a far more developed\ntype.\n\n[107] The discovery of Weinland that adult dogs are able to produce\n\u201clactase\u201d in their pancreas, whenever they are fed, quite abnormally,\nwith milk-sugar, has recently been said to be vitiated by an analytical\nmistake.\n\nDiscoveries of the last few years have taught us that almost all\nmetabolic processes in the organism, including oxidation, are carried\nout by the aid of special materials, the so-called enzymes or\nferments. These are known to exist in the most different forms even in\nthe inorganic world. They are simply chemical compounds, of specific\ntypes, that bring about chemical reactions between two other chemical\nmaterials, which in their absence would either not go on at all or would\ngo on very slowly. We cannot enter here into the much disputed chemical\ntheory of what is called \u201ccatalysis\u201d: we can only say that there is no\nobjection to our regarding almost all metabolic processes inside the\norganism as due to the intervention of ferments or catalytic materials,\nand that the only difference between inorganic and organic ferments is\nthe very complicated character of the latter and the very high degree of\ntheir specification.\n\nSuch a statement, of course, does not say that all metabolism has proved\nto be of a chemical nature: the *action* of the ferment when produced\nis chemical, but we do not know at all *how* the ferment is produced;\nwe only know that a high degree of active regulation is shown in this\nproduction. In fact, it has been proved in some cases, and probably will\nbe proved in a great many more in the near future, that all metabolic\nferments, whether they promote oxidation or assimilation proper or\nchemical decomposition, are produced in a regulatory manner with regard\nto the specific compound to be dissociated or to be built up. In this\nway the whole field of metabolism is really covered by \u201cregulations.\u201d\nAre they real \u201csecondary\u201d ones? Of course the regulatory correspondence\napplies to the process of *secretion* in the *first* place, not to the\nactual formation of the ferment inside the cell. The correspondence as\nto secretion, no doubt, is of the primary type; is there any secondary\nregulation with regard to the real *production* of the ferment? I am\nsorry that I cannot answer this question affirmatively. Nothing is\n*known* at present, even here, that really proves the existence of\nadaptation of the secondary type: there *might* be a sort of statical\n\u201charmony\u201d at the base of it all, established before all functioning\n*for* functioning.[108]\n\n[108] Compare the excellent review of the subject by Bayliss and\nStarling in the *Ergebnisse der Physiologie*, 5, 1906, p. 664. The\nreader who misses here an analysis of the brilliant discoveries\nof Pawlow and his followers, relating to so-called \u201cpsychical and\nassociative secretion,\u201d will find these facts dealt with in another\nsection of the book. These facts, indeed, would prove vitalism, it seems\nto me.\n\nThe only facts of secondary metabolic regulations which are known at\npresent have been found in combination with phenomena of restitution\nafter real disturbances of organisation, where, indeed, numbers and\nnumbers of regulatory changes of metabolism, both in animals and plants,\nhave also been recorded. But there is not one case of a secondary\nregulation really known to affect pure metabolism alone.[109] This is a\nnew indicium of the primacy of *form* in the organism.\n\n[109] It would be a true secondary metabolic regulation, if after the\nextirpation of one gland another different one were to assume its\nfunction. Nothing is known in this respect except a few rather doubtful\nobservations about the interchange of functions between thymus and\nthyroid, except also the fact that the so-called lymph-glands increase\nin size after the extirpation of the spleen. Even here, of course, a\nsort of \u201crestitution\u201d would be included in adaptation proper.\n\n\nIMMUNITY THE ONLY TYPE OF A SECONDARY PHYSIOLOGICAL ADAPTATION\n\nThere is only one class of physiological processes in which the type\nof the real secondary regulation occurs. The discoveries of the last\ntwenty years have proved beyond all doubt, and future discoveries will\nprobably prove even more conclusively, that the so-called *immunity*\nagainst diseases is but one case out of numerous biological phenomena\nin which there is an adaptive correspondence between abnormal chemical\nstimuli and active chemical reactions on the part of the organism and in\nits interior, exceeding by far everything that was formerly supposed to\nbe possible in organic regulation.\n\nThe adaptive faculty of the organism against inorganic poisonous\nsubstances[110] is but small comparatively, and is almost always due not\nto a real process of active regulation but to the action of substances\npre-existing in the organism--that is, to a sort of adaptiveness but\nnot adaptation. Metallic poisons, for instance, may be transformed into\nharmless compounds by being combined with albumen or sulphuric acid\nand thus becoming insoluble, or free acids may be neutralised, and so\non; but all these processes go on to a certain extent only, and, as\nwas mentioned already, are almost always the result of reactions with\npre-existing materials. Only in a few cases is there any sort of true\nadaptation to metallic substances, such as sublimate and, in a very\nsmall degree, arsenic, comparable in some respects with the adaptation\nto abnormally high temperatures. The organism which has been accustomed\nto receive at first very small amounts, say, of sublimate, and then\nreceives greater and greater amounts of this substance by degrees, will\nat the end of this treatment be able to stand a quantity of the poison\nthat would have been instantly fatal if administered at the first\ndose.[111] But the explanation of this adaptation is not known in any\ncase; there seems to be some similarity between it and the so-called\nhistogenetic immunity against organic poisons.\n\n[110] A good review is given by E. Fromm, *Die chemischen Schutzmittel\ndes Tierk\u00f6rpers bei Vergiftungen*, Strassburg, 1903.\n\n[111] Davenport, *Arch. Entw. Mech.* 2, 1895-1896, and Hausmann,\n*Pfl\u00fcger\u2019s Arch.* 113, 1906.\n\nIt is in the fight against animal and vegetable poisons, such as those\nproduced by bacteria, by some plants and by poisonous snakes, that the\ntrue adaptation of the organism reaches its most astonishing degree.\nThe production of so-called \u201canti-bodies\u201d in the body fluids is not the\nonly means applied against noxious chemical substances of this kind: the\nexistence of so-called histogenetic immunity is beyond all doubt, and\nMetschnikoff[112] certainly was also right in stating that the cells\nof the organism themselves repel the attack of living bacteria. Cells\nof the connective tissue and the white blood cells, being attracted by\nthem as well as by many other foreign bodies, take them in and kill\nthem. This process, called \u201cphagocytosis\u201d is of special frequency among\nlower animals, but it also contributes to what is called inflammation\nin higher ones.[113] And there are still other kinds of defence against\nparasites, as for instance the horny or calcareous membranes, employed\nto isolate trichinae and some kinds of bacteria. But all this is of\nalmost secondary importance as compared with the adaptive faculties of\nthe warm-blooded vertebrates, which produce anti-poisonous substances in\ntheir lymph and blood.\n\n[112] *Le\u00e7ons sur la pathologie compar\u00e9e de l\u2019inflammation*, Paris, 1902.\n\n[113] The other steps or phases in the process of inflammation have also\nbeen regarded as adaptive: the increased quantity of body fluid for\ninstance is said to serve to dilute poisonous substances.\n\nIt is impossible to say here[114] more than a few words about the\nphenomena and the theory of immunity proper, which have attained the\ndimensions of a separate science. Let me only mark those general points\nwhich are of the greatest theoretical interest. Discoveries of the most\nrecent years have shown not only that against the \u201ctoxins\u201d of bacteria,\nsnakes, and some plants, the organism is able actively to produce\nso-called \u201canti-toxins\u201d--that is, soluble substances which react with\nthe toxins and destroy their poisonous character--whenever required,\nbut that against any foreign body of the albumen group a specific\nreaction may occur, resulting in the coagulation of that body. But the\ndestruction of the noxious substance or foreign albumen actually present\nis not all that is accomplished by the organism. \u201cAcquired immunity\u201d\nproper, that is, security against the noxious material for a more or\nless extensive period of the *future*, depends on something more. Not\nonly is there produced as much of the so-called \u201canti-body\u201d as is\nnecessary to combine with the noxious, or at least foreign substances\nwhich are present, but *more* is produced than is necessary in the\nactual case. On this over-production depends all active immunity,\nwhether natural or, as in some kinds of vaccination, artificial; and\nso-called \u201cpassive\u201d immunity, obtained by the transfusion of the serum\nof an actively immune organism into another also depends upon this\nfeature.[115]\n\n[114] See Jacoby, *Immunit\u00e4t und Disposition*, Wiesbaden, 1906.\n\n[115] *Collected Studies on Immunity by Ehrlich and his Collaborators*,\ntranslated by Ch. Bolduan, New York and London, 1906.\n\nThis phenomenon in particular--the production of *more* of the\nantitoxin or the \u201cprecipitin\u201d than is actually necessary--seems to\nrender almost impossible any merely chemical theory of these facts. The\nreaction between toxin and antitoxin, albumen and precipitin is indeed\nchemical; it may in fact be carried out in a test-tube; but whether the\nproduction of the anti-body itself is also chemical or not could hardly\nbe ascertained without a careful and unbiassed analysis. There can be\nno doubt that the well-known theory of Ehrlich,[116] the so-called\ntheory of side-chains (\u201cSeitenkettentheorie\u201d) has given a great impulse\nto the progress of science; but even this theory, irrespective of its\nadmissibility in general, is not a real chemical one: the concept of a\nregeneration of its so-called haptophore groups is a strictly biological\nconcept.[117]\n\n[116] So-called genuine or innate immunity, in contrast to the immunity\nwhich is acquired, is of course a case of adaptedness only and not of\nadaptation. There also exists a high degree of specific adaptedness in\nsome animals with regard to their faculty of coagulating blood. (See Leo\nLoeb, *Biol. Bull.* 9, 1905.)\n\n[117] We cannot do more than barely mention here the problem of the\nlocalisation of anti-body production. In general it seems to be true\nthat anti-bodies are produced by those cells which require to be\nprotected against toxins; that would agree with the general rule, that\nall compensation of the change of any functional state proceeds from the\npart changed in its function.\n\nAnd, indeed, here if anywhere we have the biological phenomenon of\nadaptation in its clearest form. There are very abnormal changes of the\nfunctional state of the organism, and the organism is able to compensate\nthese changes in their minutest detail in almost any case. The problem\nof the specification of the reactions leading to immunity seems to me,\nas far as I can judge as an outsider, to stand at present in the very\nforefront of the science. There cannot be the slightest doubt that\nespecially against all sorts of foreign albumens the reaction is as\nstrictly specific as possible; but there are some typical cases of\nspecificity in the production of antitoxins also. It is, of course,\nthe *fact* of specific correspondence between stimulus and reaction,\nthat gives to immunity its central position among all adaptations,\nno matter whether the old hypothesis of the production of specific\nanti-bodies proves tenable, or whether, as has been urged more recently\nby some authors, the anti-body is always the same but reacts differently\naccording to the medium. In the latter case it would be the medium that\nis regulated in some way by the organism in order to attain a specific\nadaptedness.\n\n\nNO GENERAL POSITIVE RESULT FROM THIS CHAPTER\n\nBut now let us look back to the sum of all the physiological reactions\nstudied, and let us see if we have gained a new proof of the autonomy of\nlife from our long chapter.\n\nWe freely admit we have not gained any really new *proof*, but we may\nclaim, I think, to have gained many indicia for the statement that\nthe organism is not of the type of a machine, in which every single\nregulation is to be regarded as properly prepared and outlined.\n\nIt is precisely in the field of immunity that such a machine-like\npreparation of the adaptive effects seems almost impossible to be\nimagined. How indeed could there be a machine, the chemical constituents\nof which were such as to correspond adaptively to almost every\nrequirement?--to say nothing of the fact that the production of *more*\nof the protecting substance than is actually necessary could hardly be\nsaid to be \u201cchemical.\u201d\n\nIn fact, we are well entitled to say that we have reached here the very\nheart of life and of biology. If nevertheless we do not call the sum of\nour facts a real proof of vitalism, it is only because we feel unable\nto formulate the analysis of what happens in such a manner as to make\na machine as the basis of all reactions absolutely unimaginable and\nunthinkable. There *might* be a true machine in the organism producing\nimmunity with all its adaptations. We cannot disprove such a doctrine by\ndemonstrating that it would lead to a real *absurdity*, as we did in our\nanalysis of differentiation of form; there is only a very high degree of\nimprobability in our present case. But an indirect *proof* must reduce\nto *absurdity* all the possibilities except one, in order to be a proof.\n\nMechanistic explanations in all branches of functional physiology\nproper, so much in vogue twenty years ago, can indeed be said to\nhave failed all along the line: the only advantage they have brought\nto science is the clearer statement of problems to which we are now\naccustomed. But we are not fully entitled to say[118] that there never\nwill be any mechanistic explanation of physiological functions in the\nfuture. It may seem as improbable as anything can be; but we wish to\nknow not what is improbable but what is not possible.\n\n[118] Here again I should like to except from this statement the\ndiscoveries of Pawlow. See page 204, note 1.\n\nNow of course you might answer me that after we have indeed\nshown that the production of form, as occurring on the basis of\nharmonious-equipotential systems, is a fact that proves vitalism,\nthe acts taking place on the basis of that form after its production\nwould have been proved to be vitalistic also, or at least to be in\nsome connection with vitalistic phenomena. Certainly they would, and\nI myself personally should not hesitate to say so. But that is not\nthe question. We have to ask: Is any new proof, *independent of every\nother*, to be obtained from the facts of physiological adaptation in\nthemselves? And there is really none. Mere regulatory correspondence\nbetween stimuli and reactions, even if it be of the adaptive type and\noccur in almost indefinite forms, never really disproves a machine as\nits basis so long as the stimuli and reactions are *simple* and uniform.\nNext summer, however, we shall see that vitalism may be proved by such a\ncorrespondence if the two corresponding factors are not simple and not\nuniform.\n\nWe most clearly see at this point what it really was in our analysis of\ndifferentiation that allowed us to extract a real proof of vitalism from\nit. Not the mere fact of regulability, but certain specific relations\nof space, of locality, lay at the very foundation of our proof. These\nrelations, indeed, and only these relations, made it possible to\nreduce *ad absurdum* any possible existence of a machine as the actual\nbasis of what we had studied. In our next chapter again it will be\nspace-relations, though analysed in a different manner, that will enable\nus to add a second real proof of vitalism to our first one.\n\nWith this chapter we conclude the study of organic regulation in all its\nforms, as far as morphogenesis and metabolism are in question.\n\nBut our analysis of these regulations would be incomplete and indeed\nwould be open to objections, if we did not devote at least a few words\nto two merely negative topics, which will be taken more fully into\nconsideration later on.\n\n\nA FEW REMARKS ON THE LIMITS OF REGULABILITY\n\nThere has never been found any sort of \u201cexperience\u201d in regulations\nabout morphogenesis or in adaptations of the proper physiological\ntype. Nothing goes on \u201cbetter\u201d the second time than it did the first\ntime;[119] everything is either complete, whenever it occurs, or it does\nnot occur at all.\n\n[119] The few cases of an \u201cimprovement\u201d of morphogenetic acts in\nhydroids described by myself are too isolated at present to be more\nthan mere problems (*Arch. Entw. Mech.* 5, 1897). The same is true, it\nseems to me, with regard to certain recent discoveries made by R. Pearl\non *Ceratophyllum* (*Carnegie Inst. Wash. Publ.* No. 58, 1907); and by\nZeleny on a medusa (*Journ. exp. Zool.* 5, 1907). Pawlow\u2019s discovery,\nthat the enzymotic composition of the pancreatic fluid in dogs becomes\nmore and more adapted to a specific composition of the food (either meat\nor bread and milk) the longer such a specific composition is offered\nto the individual animal, may probably be understood as a case of mere\nfunctional adaptation of the cells of the digestive glands, if it stands\ncriticism at all (see Bayliss and Starling, *Ergeb. Physiol.* 5, 1906,\np. 682).\n\nThat is the first of our important negative statements about\nregulations; the second relates to the phrase just used, \u201cor it does\nnot occur at all.\u201d There are indeed limits of regulability; adaptations\nare not possible to every sort of change of the physiological state:\nsickness and death could not exist if they were; nor is restitution\npossible in all cases where it might be useful. It is a well-known fact,\nthat man is only able to heal wounds but is altogether destitute of the\nfaculty of regeneration proper. But even lower animals may be without\nthis faculty, as are the ctenophores and the nematodes for instance, and\nthere is no sort of correspondence between the faculty of restitution\nand the place in the animal kingdom. It is not altogether impossible\nthat there may be found, some day, certain conditions under which every\norganism is capable of restoring any missing part; but at present we\nknow absolutely nothing about such conditions.[120]\n\n[120] Experiments carried out in the \u201cBiologische Versuchsanstalt\u201d at\nVienna indeed have shown that many animal types are capable of at least\na certain degree of restitution, although they had previously been\ndenied this faculty by zoologists.\n\nBut no amount of negative instances can disprove an existing\npositive--which is what we have been studying. Our analysis based upon\nthe existence of regulations is as little disparaged by cases where no\nregulability exists as optical studies are by the fact that they cannot\nbe undertaken in absolute darkness.\n\n\n\n\n*D.* INHERITANCE: SECOND PROOF OF THE AUTONOMY OF LIFE\n\n\nAll organisms are endowed with the faculty of re-creating their own\ninitial form of existence.\n\nIn words similar to these Alexander Goette, it seems to me, has given\nthe shortest and the best expression of the fact of inheritance. Indeed,\nif the initial form in all its essentials is re-created, it follows from\nthe principle of univocality, that, *ceteris paribus*, it will behave\nagain as it did when last it existed.\n\nBy the fact of inheritance life becomes a rhythmic phenomenon, that is\nto say, a phenomenon, or better, a chain of phenomena, whose single\nlinks reappear at constant intervals, if the outer conditions are not\nchanged.\n\n\nTHE MATERIAL CONTINUITY IN INHERITANCE\n\nIt was first stated by Gustav Jaeger and afterwards worked out into\na regular theory by Weismann, that there is a continuity of material\nunderlying inheritance. Taken in its literal meaning this statement is\nobviously self-evident, though none the less important on that account.\nFor as all life is manifested on bodies, that is on matter, and as the\ndevelopment of all offspring starts from parts of the parent bodies,\nthat is from the matter or material of the parents, it follows that in\nsome sense there is a sort of continuity of material as long as there is\nlife--at least in the forms we know of. The theory of the continuity of\n\u201cgerm-plasm\u201d therefore would be true, even if germ-cells were produced\nby any and every part of the organism. That, as we know, is not actually\nthe case: germ-cells, at least in the higher animals and in plants, are\nproduced at certain specific localities of the organism only, and it is\nwith regard to this fact that the so-called theory of the \u201ccontinuity of\ngerm-plasm\u201d acquires its narrower and proper sense. There are distinct\nand specific lines of cell-lineage in ontogenesis, so the theory states,\nalong which the continuity of germ-protoplasm is kept up, which, in\nother words, lead from one egg to the other, whilst almost all other\nlines of cell-lineage end in \u201csomatic\u201d cells, which are doomed to\ndeath. What has been stated here is a fact in many cases of descriptive\nembryology, though it can hardly be said to be more than that. We know\nalready, from our analytical and experimental study of morphogenesis,\nthat Weismann himself had to add a number of subsidiary hypotheses to\nhis original theory to account for the mere facts of regeneration proper\nand the so-called vegetative reproduction in plants and in some animals,\nand we have learned that newly discovered facts necessitate still more\nappendixes to the original theory. In spite of that, I regard it as\nvery important that the fact of the continuity of some material as one\nof the foundations of inheritance has clearly been stated, even if the\nspecialised form of the theory, as advocated by Weismann in the doctrine\nof the \u201cgerm-lineages\u201d (\u201cKeimbahnen\u201d) should prove unable to stand\nagainst the facts.\n\nThe important problem now presents itself: What is the material, the\nmatter, which is handed down from generation to generation as the\nbasis of inheritance? Weismann, as we know, regarded it as a very\ncomplicated structure, part of which by its disintegration became the\nfoundation of individual embryology. We have disproved, on the authority\nof many facts, the latter part of this assumption; but of course the\nfirst part of it may turn out to be true in spite of this. We have no\nmeans at present to enable us to say *a priori* anything positive or\nnegative about the important question of the nature of that matter, the\ncontinuity of which in inheritance is in some sense a self-evident fact,\nand we therefore shall postpone the answer until a later point of our\nanalytical discussion.\n\n\nON CERTAIN THEORIES WHICH SEEK TO COMPARE INHERITANCE TO MEMORY\n\nIt will be advisable first to study some other theoretical views which\nhave been put forward with regard to inheritance. The physiologist\nHering, as early as 1876, compared all heredity to the well-known fact\nof memory, assuming, so to say, a sort of remembrance of all that\nhas happened to the species in the continuity of its generations;\nand several German authors, especially Semon, have lately made this\nhypothesis the basis of more detailed speculation.\n\nIt is not clear, either from Hering\u2019s paper[121] or from Semon\u2019s\nbook,[122] what is really to be understood here by the word \u201cmemory,\u201d\nand, of course, there might be understood by it very different things,\naccording to the author\u2019s psychological point of view. If he is a\n\u201cparallelist\u201d with regard to so-called psychical phenomena, he would use\nthe word memory only as a sort of collective term to signify a resultant\neffect of many single mechanical events, as far as the material world of\nhis parallel system comes into account, with which of course the problem\nof inheritance alone deals; but if he maintains the theory of so-called\npsycho-physical interaction, the psychical would be to him a primary\nfactor in nature, and so also would memory. As we have said, it is by no\nmeans clear in what sense the word \u201cmemory\u201d is used by our authors, and\ntherefore the *most* important point about the matter in question must\nremain *in dubio*.\n\n[121] *Ueber das Ged\u00e4chtnis als eine allgemeine Function der organischen\nMaterie*, Wien, 1870. New edition in *Klassiker d. exakt. Wiss.*,\nLeipzig, Engelmann.\n\n[122] *Die Mneme*, Leipzig, 1904.\n\nBut another topic is even more clear in the theory of inheritance, as\nstated in Hering\u2019s and Semon\u2019s writings. The hypothetical fact that\nso-called \u201cacquired characters\u201d are inherited is undoubtedly the chief\nassumption of that theory. Indeed, it would be difficult to understand\nthe advantage of the ambiguous word memory, had it not to call attention\nto the hypothetic fact that the organism possesses the faculty of\n\u201cremembering\u201d what once has happened to it or what it once has \u201cdone,\u201d\nso to speak, and profiting by this remembering in the next generation.\nThe zoologist Pauly indeed has stated this view of the matter in very\ndistinct and clear terms.\n\nAs we soon shall have another occasion to deal with the much-discussed\nproblem of the \u201cinheritance of acquired characters,\u201d we at present\nneed only say a few words about the \u201cmemory-theory\u201d as a supposed\n\u201cexplanation\u201d of heredity. Undoubtedly this theory postulates, either\navowedly or by half-unconscious implication, that all the single\nprocesses in individual morphogenesis are the outcome either of\nadaptations of the morphological type, which happened to be necessary\nin some former generation, or of so-called contingent \u201cvariations,\u201d of\nsome sort or other, which also happened once in the ancestral line.\nSuch a postulate, of course, is identical with what is generally called\nthe theory of descent in any of its different forms. This theory is\nto occupy us in the next lectures; at present we only analyse the\n\u201cmemory-theory\u201d as a theory of heredity in itself. In any case, to\nregard memory as the leading point in inheritance, at least if it is to\nsignify what is called memory in any system of psychology, would be to\npostulate that either adaptation or contingent \u201cvariation\u201d has been the\norigin of every morphogenetic process. Indeed, the American physiologist\nJennings did not hesitate to defend such a view most strongly, and many\nothers seem to be inclined to do the same.\n\nBut such an assumption most certainly cannot be true.\n\nIt cannot be true, because there are many phenomena in morphogenesis,\nnotably all the phenomena akin to restitution of form, which occur\nin absolute perfection even the very first time they happen. These\nprocesses, for the simple reason of their *primary perfection*, cannot\nbe due either to \u201clearning\u201d from a single adaptation, or to accidental\nvariation. We shall afterwards employ a similar kind of argument to\nrefute certain theories of evolution. It therefore may be of a certain\nlogical interest to notice that at present, combating the memory-theory\nof inheritance, and hereafter, combating certain theories of descent,\nwe select not \u201cadaptation\u201d or \u201cvariation\u201d as the central points to be\nrefuted, but the assumed *contingency* of both of them.\n\nThe word \u201cmemory,\u201d therefore, may be applied to the phenomena of\ninheritance only in a very figurative meaning, if at all. We do not\nwholly deny the possibility of an inheritance of acquired characters, as\nwill be seen later on, and to such a fact there might perhaps be applied\nsuch a term as \u201cmemory\u201d in its real sense, but we simply *know* that\nthere *is* something in inheritance which has no similarity whatever\nto what is called \u201cmemory\u201d in any species of psychology. A primary\nperfection of processes occurring quite abnormally proves that there is\na \u201cknowing\u201d of something--if we may say so--but does not prove at all\nthat there is a \u201cremembering.\u201d\n\n\nTHE COMPLEX-EQUIPOTENTIAL SYSTEM AND ITS R\u00d4LE IN INHERITANCE[123]\n\n[123] Driesch, *Organ. Regul.* 1901.\n\nBut we thus far have reached only negative results. Is the question\nnecessarily to remain at this point, which could hardly be said to be\nvery satisfying; or could we perhaps get better, that is, positive\nresults about inheritance by a change of our analytic methods? Let us\ntry to analyse the facts that occur in inheritance instead of beginning\nwith hypotheses which claim to be complete explanations. Perhaps we\nshall gain, if but small, yet certainly fixed results by an analysis\nwhich goes from the facts to the theory and not from the theory to the\nfacts.\n\nLet the discussions that are to follow be placed upon a basis as broad\nas possible.\n\nOur studies of morphogenetic restitution have shown us that besides the\nharmonious-equipotential systems another and widely different type of\nmorphogenetic \u201csystems\u201d (*i.e.* unities consisting of elements equal in\nmorphogenetic faculty) may also be the basis of restitution processes.\nWhilst in the harmonious system the morphogenetic acts performed by\nevery single element in any actual case are single acts, the totality\nof all the single acts together forming the harmonious whole, in the\nother type of systems now to be examined, complex acts, that is, acts\nwhich consist of a manifoldness in space and in time, can be performed\nby each single element, and actually are performed by one or the other\nof them. We therefore have given the title of \u201ccomplex-equipotential\nsystems\u201d to the systems in question, as all our denominations are based\non the concept of the prospective morphogenetic potency, that is of the\npossible fate of the elements.\n\nThe cambium of the Phanerogams may be regarded as the very type of a\ncomplex-equipotential system, promoting restitution of form. It runs\nthrough the whole stem of our trees, in the form of a hollow tube,\nplaced between the inner and the outer cell-layers of the stem, and\neither branch or root may originate from any single one of its cells,\njust as circumstances require. We might call the cambium a system of the\n\u201ccomplex\u201d type of course, even if every one of its constituents were\nable to form only a root or only a branch by way of restitution. But in\nfact one and the same element can form both of these complex-structures;\nit depends only on its relative position in the actual part of the stem\nisolated for the purposes of experiment, what will be accomplished in\nevery case. Here we have a state of affairs, which we shall encounter\nagain when studying regeneration in animals: every element of the system\nmay be said to contain potencies for the \u201cideal whole,\u201d though this\nideal whole will never be realised in its proper wholeness.[124]\n\n[124] The \u201cideal whole\u201d is also proved to exist, if any *given*\n\u201cAnlage,\u201d say of a branch, is forced to give origin to a root, as has\nreally been observed in certain plants. This case, like many other\nless extreme cases of what might be called \u201ccompensatory heterotypy,\u201d\nare best to be understood by the aid of the concept of \u201cprospective\npotency.\u201d It is very misleading to speak of a metamorphosis here. I\nfully agree with Kra\u0161an about this question. See also page 112, note 1,\nand my *Organ. Regul.* pp. 77, 78.\n\nBut there is no need to recur to the \u201cideal whole\u201d in many other cases\nof adventitious restitution in plants. On isolated leaves of the\nwell-known begonia, a whole plant, containing all the essential parts,\nmay arise from any single cell[125] of the epidermis, at least along the\nveins, and in some liverworts it has been shown by V\u00f6chting, that almost\nevery cell of the whole is able to reproduce the plant, as is also the\ncase in many algae.\n\n[125] Winkler has discovered the important fact, that the adventitious\nbuds formed upon leaves may originate either from one single cell of\nthe epidermis or from several cells together; a result that is very\nimportant with respect to the problem of the distribution of \u201cpotencies.\u201d\n\nIn the animal kingdom it is chiefly and almost solely the phenomena\nof regeneration proper which offer typical instances of our systems,\nsince adventitious restitution, though occurring for instance in the\nrestitution of the lens of vertebrates from the iris, and though\nconnected also with the events in regeneration proper,[126] is of but\nsecondary importance in animal restitution, at least, if compared with\nrestitution in plants. If we study the regeneration of a leg in the\ncommon newt, we find that it may take place from every section, the\npoint of amputation being quite at our choice. Without regarding here\nthe exact order of the regeneration phenomena, which is almost unknown\nat present, we in any case can say without any doubt that the line\nof consecutive possible cross-sections forms a complex-morphogenetic\nsystem, as every one of them is able to give rise to a complex organ,\nviz. the foot and part of the leg. It is an open question whether this\ncomplex system is to be called \u201cequipotential\u201d or not. It indeed seems\nto be inequipotential at the first glance, for each single section has\nto form a different organogenetic totality, namely, always that specific\ntotality which had been cut off; but if we assume hypothetically that\nthe real \u201cAnlage\u201d which is produced immediately by the cells of the\nwounded surface is the very same for all of them, and that it is the\nactual state of organisation which determines to what result this\nAnlage is to lead,[127] we may say that the series of consecutive\ncross-sections of a newt\u2019s leg does form a morphogenetic system of the\ncomplex-equipotential type, promoting secondary regulations of form.\n\n[126] The \u201cregeneration\u201d of the brain of annelids for instance is far\nbetter regarded as an adventitious formation than as regeneration\nproper: nothing indeed goes on here at the locality of the wound; a new\nbrain is formed out of the ectoderm at a certain distance from it.\n\n[127] A full \u201canalytical theory of regeneration\u201d has been developed\nelsewhere (*Organ. Regul.* p. 44, etc.). I can only mention here that\nmany different problems have to be studied by such a theory. The\nformation of the \u201cAnlage\u201d out of the body and the differentiation of\nit into the completely formed results of regeneration are two of them.\nThe former embraces the question about the potencies not only of the\nregenerating body but of the elements of the Anlage also; the latter\nhas to deal with the specific order of the single acts of regenerative\nprocesses.\n\nNow all these difficulties vanish, if we consider the regeneration of\nanimals, such for instance as many worms of the annelid class or our\nfamiliar ascidian *Clavellina*, in which regeneration in both directions\nis possible. The wound at the posterior end of the one half which\nresults from the operation forms a posterior body half, the wound at\nthe anterior end of the other half forms an anterior one. Again, it is\nthe ideal whole which we meet here: each section of the body indeed may\nbe said to contain the potencies for the production of the totality,\nthough actually this totality is always realised by the addition of two\npartial organisations. The title of complex-equipotential systems thus\nseems to be fully justified as applied to the systems which are the\nbasis of regeneration: each section of the regenerating body may in fact\nproduce the same complex whole, or may, if we prefer to say so, at least\nprepare the ground for that complex Anlage, out of which the complex\ntotality is actually to arise, in the same manner.\n\nIt often occurs in science, that in rather strange and abnormal\nconditions something becomes apparent which might have been found\neverywhere, which is lying before our eyes quite obviously. Are\nwe not in just such a condition at present? In order to study the\ncomplex-equipotential systems, we turn to the phenomena of regeneration\nand of restitution in general; we occasionally even introduce hypotheses\nto render our materials more convenient for our purposes; and all the\ntime there is one sort of complex-equipotential system in the body of\nevery living being, which only needs to be mentioned in order to be\nunderstood as such, and which indeed requires no kind of preliminary\ndiscussion. The system of the propagation cells, in other words the\nsexual organ, is the clearest type of a complex-equipotential system\nwhich exists. Take the ovary of our sea-urchin for instance, and there\nyou have a morphogenetic system every element of which is equally\ncapable of performing the same complex morphogenetic course--the\nproduction of the whole individual.\n\nFurther on we shall deal exclusively with this variety of our systems,\nand in doing so we shall be brought back to our problem of heredity. But\nit had its uses to place our concept of the complex-equipotential system\nupon such a broad basis: we at once gave a large range of validity to\nall that is to follow--which, indeed, does not apply to inheritance\nalone, though its significance in a theory of heredity may be called its\nmost important consequence.\n\n\nTHE SECOND PROOF OF LIFE-AUTONOMY. ENTELECHY AT THE BOTTOM OF INHERITANCE\n\nAfter we had established the concept of the harmonious-equipotential\nsystem in a former chapter, we went on to study the phenomena of the\ndifferentiation of it, and in particular the problem of the localisation\nof all differentiations. Our new concept of the complex-equipotential\nsystem is to lead us to an analysis of a different kind: we shall pay\nspecial attention to the origin, to the *genesis* of our complex systems\nthat show equipotentiality.\n\nIf we review the process of ontogenesis, we are able to trace back every\ncomplex system to a very small group of cells, and this small group of\ncells again to one single cell. So in plants the cambium may be shown\nto have originated in a sort of tissue-rudiment, established at a very\nearly period, and the ovary may be demonstrated to be the outcome of a\ngroup of but a few cells, constituting the first visible \u201cAnlage\u201d of the\nreproductive organs. At the end then, or from another point of view at\nthe beginning, a single cellular element represents the very primordial\negg-cell.\n\nThe whole cambium, there can be no doubt, must be regarded as the result\nof a consecutive number of cell-divisions of the one cell from which it\noriginates. So must it be with the ovary. The primordial egg-cell has\nundergone a long line of consecutive divisions; the single eggs are the\nlast result of them.\n\nWe now proceed to some considerations which have a certain\nlogical similarity to those which inaugurated our analysis of the\ndifferentiation of the harmonious-equipotential systems, though the\nfacts in question are very different.\n\nViewed by itself without any kind of prepossessions, as it might\nbe by any one who faces a new problem with the single postulate of\nintroducing new natural entities--to use the scholastic phrase--as\nlittle as possible, the development of the single egg might be regarded\nas proceeding on the foundation of a very complicated sort of machine,\nexhibiting a different kind of construction in the three chief\ndimensions of space, as does also the organism which is to be its result.\n\nBut could such a theory--irrespective of all the experimental facts\nwhich contradict it--could such a theory stand before the *one* fact,\nthat there occurs a *genesis* of that complex-equipotential system,\nof which our one single egg forms a part? Can you imagine a very\ncomplicated machine, differing in the three dimensions of space, to\nbe divided hundreds and hundreds of times and in spite of that to\nremain always the same whole? You may reply that during the period\nof cell-divisions there is still no machine, that the machine is\nestablished only after all the divisions are complete. Good; but what\nthen constructs this machine in the definitive cells of our systems, say\nin the eggs? Another sort of machine perhaps? That could hardly be said\nto be of much use. Or that entelechy of which we have spoken? Then you\nwould recur to our first proof of vitalism and would burden entelechy\nwith a specific performance, that is with the construction of the\nhypothetic machine which you are postulating in every single egg. But of\ncourse you would break the bounds of physics and chemistry even then.\n\nIt seems to me that it is more simple, and so to say more natural, not\nto recur to our first proof of life-autonomy in order to keep to the\n\u201cmachine theory\u201d in this new branch of inquiry, but to consider facts as\nthey offer themselves to analysis.\n\nBut then indeed we are entitled to draw an independent second proof of\nthe autonomy of life from our analysis of the genesis of systems of the\ncomplex-equipotential type. We say it is a mere absurdity to assume that\na complicated machine, typically different in the three dimensions of\nspace, could be divided many many times, and in spite of that always\nbe the whole: therefore there cannot exist any sort of machine as the\nstarting-point and basis of development.\n\nLet us again apply the name entelechy to that which lies at the very\nbeginning of all individual morphogenesis.\n\nEntelechy thus proves to be also that which may be said to lie at\nthe very root of inheritance,[128] or at least of the outcome of\ninheritance; the individual formation of the next generation is shown\nnot to be performed by a machine but by a natural agent *per se*.\n\n[128] And, of course, at the root of every new starting of certain\nparts of morphogenesis also, as in regeneration and in adventitious\nbudding; these processes, as we know, being also founded upon\n\u201ccomplex-equipotential systems,\u201d which have had their \u201cgenesis.\u201d\n\n\nTHE SIGNIFICANCE OF THE MATERIAL CONTINUITY IN INHERITANCE\n\nBut what about the material continuity appearing in inheritance, which\nwe have said to be almost self-evident, as life is only known to exist\non material bodies? Is there not, in fact, a serious contradiction\nin admitting at the same time entelechy on the one side and a sort\nof material condition on the other as the basis of all that leads to\nand from inheritance? Next summer the relation between matter and our\nautonomous agent of life will be studied more fully; at present it must\nbe enough to state in a more simple and realistic way, what we hold\nthis relation to be. There is no contradiction at all in stating that\nmaterial continuity is the basis of inheritance on the one side, and\nentelechy on the other. It would be very inconvenient for us if there\nwere any: for the material continuity is a mere fact and our entelechy\nwe hope we have proved to exist also; if now there were any sort of\ncontradiction in assuming the existence of both of them, of course it\nwould be fatal to our proof.\n\nLet us try to comprehend what is meant by the statement that entelechy\nand something material are at work in inheritance at the same time.\nEntelechy has ruled the individual morphogenesis of the generation which\nis regarded as being the starting-point for inheritance, and will rule\nalso the morphogenesis of the generation which is to follow; entelechy\ndetermines the egg to be what it is, and the morphogenesis starting from\nthis egg to be what it is also. Entelechy, at present, is not much more\nfor us than a mere word, to signify the autonomous, the irreducible of\nall that happens in morphogenesis with respect to *order*, in the one\ngeneration and in the next. But may not the material continuity which\nexists in inheritance account perhaps for the material elements *which\nare to be ordered*? In such a way, indeed, I hope we shall be able to\nreconcile entelechy and the material basis of heredity. May it not be\nthat there exist some \u201cmeans\u201d for morphogenesis, which are handed down\nfrom generation to generation, always controlled by entelechy, and which\nconstitute the real significance of the continuity of matter during\ninheritance?\n\n\nTHE EXPERIMENTAL FACTS ABOUT INHERITANCE\n\nDiscoveries of the last few years do seem to show that such means\nof a material character, though not the foundation of that order of\nprocesses which is inherited, are nevertheless among the most necessary\nconditions for the accomplishment of inheritance in general. It is\nscarcely necessary to remind you that for very many years all concrete\nresearch on heredity proper--that is, the actual comparison of the\nvarious specific characters in the generations of the grandfather, the\nfather, and the child--was due to Galton. You may also be aware that in\nspite of Galton\u2019s inestimable services it was not till 1900 that one of\nthe active principles concerned in inheritance was found independently\nby de Vries, Correns, and Tschermak, and that this principle happened\nto be one that *had* been discovered already, stated with the utmost\nclearness and precision by the Augustinian monk, Gregor Mendel,[129] as\nearly as 1865, though it had been completely forgotten ever since.\n\n[129] New edition in the \u201cKlassiker d. exakt. Wiss.\u201d Leipzig, Engelmann;\nsee also Bateson, *Mendel\u2019s Principles of Heredity*, Cambridge, 1902.\n\nThe so-called \u201crule of Mendel\u201d is based upon experiments with hybrids,\nthat is, with the offspring of parents belonging to different species,\nor, at least, varieties, but it relates not to the characters of the\ngeneration resulting immediately from hybridisation, the \u201cfirst\u201d\ngeneration of hybrids, as we shall call it, but to the characters of\nthat generation which is the result of crossing the hybrids with each\nother, provided that this leads to any offspring at all. There are many\ncases indeed, both amongst animals and plants, where the offspring of\nthe hybrids, or in other terms the \u201csecond\u201d generation, is found to\nconsist of individuals of three different types--the mixed[130] type\nof the hybrids themselves, and the two pure types of the grandparents.\nWhenever the individuals of the \u201csecond\u201d generation are separated into\nthese three different types, hybrids are said to \u201csplit.\u201d It is the\nfact of this splitting on the one hand, and on the other hand a certain\nstatement about the numbers of individuals in the three different types\nof the \u201csecond\u201d generation, that gives its real importance to Mendel\u2019s\nrule.\n\n[130] For the sake of simplicity I shall not deal here with those\ncases of hybridisation in which one quality is \u201crecessive,\u201d the other\n\u201cdominant,\u201d but only allude to the cases, less numerous though they be,\nwhere a real mixture of maternal and paternal qualities occurs.\n\nBefore discussing what may follow from Mendel\u2019s discovery for the\ntheory of heredity, we must lay stress on the fact that there are many\nexceptions to his rule. In quite a number of cases the hybrids are of\none or more types, which remain constant: there is no splitting at all\nin the second generation. But that does not affect the rule of Mendel in\nthose cases where it is true. Where there is a \u201csplitting\u201d in the second\ngeneration, there also are the numerical proportions stated by Mendel;\nthere never are other relations among the numbers of individuals of the\nmixed and of the two pure types than those given by his rule. I regard\nit as very important that this real meaning of Mendel\u2019s principle should\nbe most clearly understood.\n\nFrom the fact of the splitting of hybrids in the second generation most\nimportant consequences may be drawn for the theory of inheritance; the\nsplit individuals, if crossed with each other, always give an offspring\nwhich remains pure; there is no further splitting and no other change\nwhatever. The germ-cells produced by the split individuals of the second\ngeneration may therefore be said to be \u201cpure,\u201d as pure as were those of\nthe grandparents. But that is as much as to say that the pureness of\nthe germ-cells has been preserved in spite of their passing through the\n\u201cimpure\u201d generation of the hybrids, and from this fact it follows again\nthat the union of characters in the hybrids must have been such as to\npermit pure separation: in fact, the germ-cells produced by Mendelian\nhybrids may hypothetically be regarded as being pure themselves.[131]\n\n[131] This hypothesis was first suggested by Sutton and is at present\nheld by orthodox Mendelians; but probably things are a little more\ncomplicated in reality, as seems to be shown by some facts in the\nbehaviour of so-called \u201cextracted recessives.\u201d In Morgan\u2019s *Experimental\nZoology*, New York, 1907, a full account of the whole matter is given.\n\nWe have not yet considered one feature of all experiments in\nhybridisation, which indeed seems to be the most important of all for\nthe theory of inheritance, if taken together with the fact of the\npureness of the germs. The rule of Mendel always relates to one single\ncharacter of the species or varieties concerned in hybridisation, and\nif it deals with more than one character, it regards every one of them\nseparately; indeed, the rule holds for every one of them irrespective\nof the others. We cannot study here how this most important fact of\nthe independence of the single characters of a species with regard to\ninheritance leads to the production of new races, by an abnormal mixture\nof those characters. We only take advantage of the fact theoretically,\nand in doing so, I believe, we can hardly escape the conclusion that\nthe independence of the single characters in inheritance, taken\ntogether with the pureness of the germ-cells in the most simple form\nof hybrids, proves that there occurs in inheritance a sort of handing\nover of single and separate morphogenetic agents which relate to the\nsingle morphogenetic characters of the adult. We may use Bateson\u2019s\nword \u201callelomorphs\u201d for these agents, or units, as they may be called,\nthereby giving expression to the fact that the single and separate\nunits, which are handed over in inheritance, correspond to each other in\nnearly related species without being the same.\n\nAnd so we have at least an inkling of what the material continuity of\ninheritance is to mean, though, of course, our \u201csingle and separate\nmorphogenetic agents,\u201d or \u201cunits\u201d or \u201callelomorphs\u201d are in themselves\nnot much more than unknown somethings described by a word; but even then\nthey are \u201csomethings.\u201d\n\nBesides the researches relating to the rule of Mendel and its\nexceptions, founded, that is, upon a study of the \u201csecond\u201d generation of\nhybrids, there is another important line of research lately inaugurated\nby Herbst, which investigates the first generation in hybridisation.\nThe hybrids themselves are studied with the special purpose of finding\nout whether the type of the single hybrid may change according to the\nconditions of its development, both outer and inner. The discoveries\nthus made may lead some day to a better understanding of the intimate\nnature of the \u201cunits\u201d concerned in heredity, and perhaps to some\nknowledge of the arranging and ruling factor in morphogenesis also.\n\nStarting from the discovery of Vernon, that the hybrids of sea-urchins\nare of different types according to the season, Herbst[132] was able\nto show that differences among the hybrids with regard to their being\nmore of the paternal or more of the maternal type, are in part certainly\ndue to differences in temperature. But there proved to be still another\nfactor at work, and Herbst has succeeded in discovering this factor by\nchanging the internal conditions of morphogenesis. Whenever he forced\nthe eggs of *Sphaerechinus* to enter into the first[133] phase of\nartificial parthenogenesis and then fertilised them with the sperm of\n*Echinus*, he was able to approximate the offspring almost completely\nto the maternal type, whilst under ordinary conditions the hybrids in\nquestion follow the paternal far more than the maternal organisation.\n\n[132] *Arch. Entw. Mech.* 21, 22, and 24, 1906-7; see also Doncaster,\n*Phil. Trans. Royal Soc.* London, B. 196, 1903. The influence of\ndifferent temperature upon the organisation of the hybrids is not\nalways quite pure, inasmuch as the paternal and the maternal forms may\nthemselves be changed by this agent. In spite of that there exists an\ninfluence of the temperature upon the hybrid *as such*, at least with\nregard to certain features of its organisation.\n\n[133] Only the nucleus of the egg had entered its first stages of\nactivity.\n\nWhat is shown, in the first place, by these discoveries is the\nimportance of an arranging and ruling factor in spite of all units. The\norganism is always one *whole* whether the paternal properties prevail\nor the more complicated maternal ones; in other words, all so-called\nproperties that consist in the *spatial relations of parts* have nothing\nto do with \u201cunits\u201d or \u201callelomorphs,\u201d which indeed cannot be more\nthan necessary means or materials, requiring to be ordered. As to the\ncharacter of the morphogenetic single and separate units themselves\nHerbst is inclined to regard them as specific chemical substances which\nunite correspondingly during nuclear conjugation, forming a sort of\nloose chemical compound. It would depend on the constitution of this\ncompound whether germ-cells of hybrids could become pure or not.\n\n\nTHE R\u00d4LE OF THE NUCLEUS IN INHERITANCE\n\nAt the end of our studies on heredity we hardly can avoid saying a\nfew words about the problem of the localisation of the morphogenetic\nunits in the germ-cells themselves. Is it in the protoplasm or in the\nnucleus that they are placed? You all know that this question was for\na long time regarded as more important than any other, and perhaps\nyou have already blamed me for not raising it until now. But in my\nopinion results gained by the purely analytical method and carefully\nestablished, are always superior to those which are of a merely\ndescriptive nature and doubtful besides. The famous problem of the part\nplayed by the nucleus in inheritance is both descriptive and doubtful:\nit is only, so to say, of factual, not of analytical importance, and\nquite insoluble at present.\n\nAs for our second proof of vitalism, stating that no kind of machine\ninside the germ-cells can possibly be the foundation of their\nmorphogenesis, it is clear that the protoplasm and the nucleus may both\ncome into account here on equal terms. If you prefer to say so, it is to\nthe nucleus and to its division in particular that the second proof of\nautonomy relates, while the first, though not over-looking the presence\nof nuclei,[134] deals \u201cespecially\u201d with the protoplasmic nature of its\n\u201csystems.\u201d\n\n[134] The first proof of vitalism, indeed, rests upon the analysis of\nthe differentiation of an harmonious-equipotential system as a *whole*:\nthis *whole* cannot be a machine that would relate to differentiation as\na *whole*; the question whether there might be any machines distributed\n*in* the whole, in the form of the nuclei is of no importance at all in\nthis argument. Moreover the pressure experiments (see page 63) prove the\nunimportance of such \u201cmachines\u201d for the specificity of differentiation,\nand the second proof of vitalism shows that the nuclei cannot be\nregarded as machines accounting for differentiation in *any* way.\n\nWhat then can we say, on the basis of actual facts, about the part taken\nby the protoplasm and by the nucleus in inheritance, now that we have\nlearnt from our analytical discussion that both of them cannot be any\nkind of morphogenetic machine, but can only be means of morphogenesis?\nLet us state our question in the following way: whereabouts in the\ngerm-cells are those \u201cmeans\u201d of morphogenesis localised, the existence\nof which we infer from the material continuity in the course of\ngenerations in general and from the facts discovered about hybridisation\nin particular?\n\nThe first of the facts generally said to support the view that the\nnucleus of the germ-cells exerts a specified influence upon the\nprocesses of development and inheritance, relates to the proportion\nbetween protoplasm and nuclear material in the egg and in the spermiae.\nThis proportion is very different in the two sexual products, as we\nknow, there being an enormous preponderance of the protoplasm in the\negg, of the nucleus in the spermatozoon. This seems to indicate that\nthe proportion between protoplasm and nucleus is fairly indifferent\nfor inheritance, as all the facts go to show that inheritance from\nthe father is as common as inheritance from the mother. It is in the\nnucleus, and in the nucleus alone, that any similarity of organisation\nexists between the two sexual products, so very different in all other\nrespects: therefore the nucleus should be the organ of inheritance. The\nphenomena of nuclear division, of karyokinesis, which are quite equal in\nboth sexual cells, are certainly well fitted to support this hypothesis.\n\nThere seems indeed to be some truth in this reasoning, but nevertheless\nit must remain hypothetical; and it must never be forgotten that\nthere may be very probably some sort of morphogenetic importance in\nprotoplasm also. Rauber and afterwards Boveri[135] have tried to prove\nexperimentally that it is on the nuclear chromatic substance only that\ninheritance depends, but the first of these authors failed to get any\nresults at all, and the latter obtained only ambiguous ones. Godlewski,\non the contrary, has fertilised purely protoplasmic egg-fragments of\nthe sea-urchin with the sperm of quite another group of Echinoderms,\nand obtained in spite of that a few stages of development of the\npure maternal type. This experiment seems to place the morphogenetic\nimportance of protoplasm beyond all doubt.\n\n[135] Boveri tried to fertilise enucleated fragments of the egg of\n*Sphaerechinus* with the sperm of *Echinus*. He failed to get any\nresults in isolated experiments, but found a few small larvae of the\npure *Echinus* type in large cultures consisting of shaken eggs. But\nlater experiments on hybridisation in sea-urchins have shown that a full\nhybrid of *Echinus* and *Sphaerechinus* may be purely paternal also.\n\nI should prefer not to make any definite statement about our problem at\npresent. Our actual knowledge of the organisation and metabolism of both\nnucleus and protoplasm is so extremely small and may relate to such very\ninsignificant topics, that any definite decision is impossible. I myself\nbelieve that the nucleus plays an important part in heredity, perhaps\neven a greater one than protoplasm, but this is only my belief.[136]\n\n[136] Surely the new results of Herbst, mentioned above, are another\nindication of the importance of something in the nucleus. The first\nstage in parthenogenesis, which he used in his experiments, is a nuclear\nphenomenon.\n\nThe discovery of Gruber and others, that Protozoa are only capable of\nrestitution if they contain at least a fragment of the nucleus, has\nalso been used occasionally as a proof of the morphogenetic importance\nof the nucleus. But might not this absence of restitution where nuclear\nmaterial is lacking be understood equally well on the hypothesis of Loeb\nand R. S. Lillie that the nucleus is a centre of oxidation in the cell?\nRemove the heart from a vertebrate and the animal will not digest any\nmore; but in spite of that the heart is not the organ of digestion.\n\nAnd so we lay stress once more upon this point: that the experimental\nresults of hybridisation and the analytical results obtained by the\ndiscussion of the complex-equipotential systems are of greater value\nto the theory of heredity than all speculation about the importance or\nunimportance of special constituents of the cell, of whose organisation,\nchemistry, and physics, scarcely anything is known at present.[137]\n\n[137] Boveri (*Ergebn. \u00fcb. d. Konstitution etc. des Zellkerns*, Jena,\n1904; and \u201cZellen-Studien VI.\u201d *Jen. Zeitschr.* 43, 1907) has made it\nhighly probable by experiments that the different chromosomes of the\nnucleus of the sexual products play a different part in morphogenesis,\nthough not in the sense of different single representatives of\ndifferent single organs. This doctrine, of course, would not alter\nthe whole problem very much: the chromosomes would only be *means* of\nmorphogenesis and nothing else, no matter whether they were of equal or\nof different formative value. It only is with regard to the problem of\nthe determination of sex (see page 107, note 3), that the morphogenetic\nsingularity of *one* certain specific chromosome can be said to be\nproved.\n\n\nVARIATION AND MUTATION\n\nHeredity, it has been said, may be understood as resting upon the fact\nthat each organism forms its own initial stage again, and that this\ninitial stage always encounters conditions of the same kind.\n\nIf this statement were quite correct, all the individuals of a given\nspecies would be absolutely alike everywhere and for ever. But they\nare not alike; and that they are not alike everywhere and for ever is\nnot merely the only real foundation of the so-called theory of descent\nwe possess, but also forces us to change a little our definition of\nheredity, which now proves to have been only a sort of approximation to\nthe truth, convenient for analytical discussion.\n\nIn the first place, the conditions which surround the initial stages\nof morphogenesis are not quite equal in every respect: and indeed\nthe offspring of a given pair of parents, or better, to exclude all\ncomplications resulting from sexual reproduction, or amphimixis, as\nWeismann called it--the offspring of one given parthenogenetic female\nare not all equal among themselves. The individuals of each generation\nare well known to vary, and it is especially in this country that the\nso-called individual or fluctuating variation has been most carefully\nstudied by statistical methods, Galton and Weldon being the well-known\npioneers in this field.[138] In fact, if we are allowed to assume that\nthis sort of variation is the outcome of a variation of conditions--in\nthe most general meaning of the word--we only follow the opinion\nwhich has almost universally been adopted by the biologists[139] that\nare working at this branch of the subject. Variation proper is now\ngenerally allowed to be the consequence of variations in nutrition;\nthe contingencies of the latter result in contingencies of the former,\nand the law of contingencies is the same for both, being the most\ngeneral law of probability. Of course under such an aspect fluctuating\nvariation could hardly be called an exception, but rather an addition to\ninheritance.\n\n[138] H. M. Vernon, *Variations in Animals and Plants*, London, 1903.\n\n[139] De Vries, *Die Mutationstheorie*, i., 1901; and Klebs, *Jahrb.\nwiss. Bot.* 42, 1905.\n\nBut there are other restrictions of our definition of heredity. The\ninitial stage which is formed again by an organism is not always quite\nidentical in itself with the initial stage of its own parent: Bateson\nand de Vries were the first to study in a systematic way these real\nexceptions[140] to true inheritance. As you know, de Vries has given\nthem the name of \u201cmutations.\u201d What is actually known on this subject is\nnot much at present, but nevertheless is of great theoretical value,\nbeing the only real foundation of all theories of descent, as we shall\nsee in the next lectures. \u201cMutations\u201d are known to exist at present only\namong some domesticated animals and plants. Nothing of a more general\ncharacter can be said about their law or meaning.[141]\n\n[140] They would not be \u201creal exceptions\u201d if Klebs (*Arch. Entw. Mech.*\n24, 1907) were right in saying that both variations and mutations owe\ntheir existence to external agents. What is really *proved* by Klebs\nis the possibility of changing the *type* of a curve of variation and\nof provoking certain discontinuous varieties by external means. See\nalso Blaringhem (*Comptes rend.* 1905-6, and *Soc. de Biol.* 59, 1905),\nand MacDougal (*Rep. Depart. Bot. Res., 5th Year-book Carnegie Inst.*,\nWashington, 129).\n\n[141] H. de Vries, *Species and Varieties: their Origin by Mutation*,\nLondon, 1905. A short review of the \u201cmutation-theory\u201d is given by Franc\u00e9\nin *Zeitschrift f. d. Ausbau d. Entwickelungslehre*, i. 1907. It is well\nknown that Gautier, and, in the first place, Korshinsky, advocated a\nsimilar view previous to the authors named in the text.\n\n\n\n\nCONCLUSIONS FROM THE FIRST MAIN PART OF THESE LECTURES\n\n\nIn finishing our chapter on inheritance, we at the same time have\nfinished the first main part of our lectures; that part of them which\nhas been devoted exclusively to the study of the morphogenesis of the\n*individual*, including the functioning of the adult individual form.\nWe now turn to our second part, which is to deal with the problems of\nthe diversities of individual forms, with morphological systematics. The\nend of our chapter on inheritance has already led us to the threshold of\nthis branch of biological science.\n\nThe chief result of the first main part of our lectures has been to\nprove that an autonomy of life phenomena exists at least in some\ndepartments of individual morphogenesis, and probably in all of them;\nthe real starting-point of all morphogenesis cannot be regarded as a\nmachine, nor can the real process of differentiation, in all cases where\nit is based upon systems of the harmonious equipotential type. There\ncannot be any sort of machine in the cell from which the individual\noriginates, because this cell, including both its protoplasm and its\nnucleus, has undergone a long series of divisions, all resulting in\nequal products, and because a machine cannot be divided and in spite of\nthat remain what it was. There cannot be, on the other hand, any sort\nof machine as the real foundation of the whole of an harmonious system,\nincluding many cells and many nuclei, because the development of this\nsystem goes on normally, even if its parts are rearranged or partly\nremoved, and because a machine would never remain what it had been in\nsuch cases.\n\nIf our analytical discussions have thus led us to establish a typical\nkind of vitalism, it follows that we can by no means agree with Wilhelm\nRoux in his denomination of the analytical science of the individual\nform and form-production as \u201cEntwickelungsmechanik,\u201d \u201cdevelopmental\nmechanics,\u201d a title, which, of course, might easily be transformed\ninto that of \u201cmorphogenetic mechanics,\u201d to embrace not only normal\ndevelopment, but restitution and adaptation too. We feel unable to speak\nof \u201cmechanics\u201d where just the contrary of mechanics, in the proper\nmeaning of the word, has been proved to exist.\n\nNames of course are of comparatively small importance, but they\nshould never be allowed to be directly misleading, as indeed the term\n\u201cEntwickelungsmechanik\u201d has already proved to be. Let us rather say,\ntherefore, that we have finished with this lecture that part of our\nstudies in biology which has had to deal with morphogenetic physiology\nor physiological morphogenesis.\n\nOnce more we repeat, at this resting-point in our discussions, that both\nof our proofs of life-autonomy have been based upon a careful analysis\nof certain facts about the distribution of morphogenetic potencies in\ntwo classes of morphogenetic systems, and upon nothing else. To recall\nonly one point, we have not said that regeneration, merely because it\nis a kind of restitution of the disturbed whole, compels us to admit\nthat biological events happen in a specific and elemental manner, but,\nindeed, regeneration *does* prove vitalism, because it is founded upon\nthe existence of certain complex-equipotential systems, the analysis of\nthe genesis of which leads to the understanding of life-autonomy. This\ndistinction, in fact, is of the greatest logical importance.\n\n\n\n\nPART II\n\nSYSTEMATICS AND HISTORY\n\n*A.* THE PRINCIPLES OF SYSTEMATICS\n\n\nRATIONAL SYSTEMATICS\n\nAll systematics which deserves the predicate \u201crational\u201d is founded\nupon a concept or upon a proposition, by the aid of which a totality\nof specific diversities may be understood. That is to say: every\nsystem claiming to be rational gives us a clue by which we are able to\napprehend either that there cannot exist more than a certain number of\ndiversities of a certain nature, or that there can be an indefinite\nnumber of them which follow a certain law with regard to the character\nof their differences.\n\nSolid geometry, which states that only five regular bodies are possible,\nand points out the geometrical nature of these bodies, is a model\nof what a rational system should be. The theory of conic sections\nis another. Take the general equation of the second degree with two\nunknowns, and study all the possible forms it can assume by a variation\nof its constants, and you will understand that only four different types\nof conic sections are possible--the circle, the ellipse, the hyperbola,\nand the parabola.\n\nIn physics and chemistry no perfect rational systems have been\nestablished hitherto, but there are many systems approaching the ideal\ntype in different departments of these sciences. The chemical type of\nthe monohydric saturated alcohols, for instance, is given by the formula\nC_nH_{2n+1}OH, and in this formula we not only have an expression of\nthe law of composition which all possible alcohols are to follow,--but,\nsince we know empirically the law of quantitative relation between\n*n* and various physical properties, we also possess in our formula a\ngeneral statement with respect to the totality of the properties of any\nprimary alcohol that may be discovered or prepared in the future. But\nchemistry has still higher aims with regard to its systematics: all of\nyou know that the so-called \u201cperiodic law of the elements\u201d was the first\nstep towards a principle that may some day give account of the relation\nof all the physical and chemical properties of any so-called element\nwith its most important constant, the atomic weight, and it seems to be\nreserved for the present time to form a real fundamental system of the\n\u201celements\u201d on the basis of the periodic law by the aid of the theory\nof electrons. Such a fundamental system of the elements would teach us\nthat there can only be so many elements and no more, and only of such a\nkind. In crystallography a similar end has been reached already by means\nof certain hypothetic assumptions, and systematics has here accounted\nfor the limited number and fixed character of the possible forms of\ncrystalline symmetry.\n\nIt is not difficult to understand the general logical type of all\nrational systems, and logic indeed can discover it without appealing\nto concrete sciences or to geometry. Rational systematics is always\npossible whenever there exists any fundamental concept or proposition\nwhich carries with it a principle of division; or to express it somewhat\ndifferently, which would lead to contradictions, if division were to\nbe tried in any but one particular manner. The so-called \u201cgenus,\u201d as\nwill easily be perceived, then embraces all its \u201cspecies\u201d in such a\nmanner that all peculiarities of the species are represented already in\nproperties of the genus, only in a more general form, in a form which\nis still unspecified. The genus is both richer in content and richer in\nextent than are the species, though it must be added that its richness\nin content is, as it were, only latent: but it may come into actuality\nby itself and without any help from without.\n\nWe are dealing here with some of the most remarkable properties of the\nso-called synthetic judgments *a priori* in the sense of Kant, and,\nindeed, it seems that rational systematics will only be possible where\nsome concept of the categorical class or some proposition based upon\nsuch concept lies at the root of the matter or at least is connected\nwith it in some way. In fact, all rational systems with regard to the\nrelations of symmetry in natural bodies deal ultimately with space; or\nbetter, all systems in such fields are able to become rational only if\nthey happen to turn into questions of spatial symmetry.\n\nAll other genera and species, whether of natural bodies or of facts,\ncan be related only on the basis of empirical abstraction, *i.e.* can\nnever attain rationality: here, indeed, the genus is richer in extent\nand poorer in content than are the species. The genus is transformed\ninto the species, not by any inherent development of latent properties,\nbut by a mere process of addition of characteristic points. It is\nimpossible to deduce the number or law or specifications of the species\nfrom the genus. Mere \u201cclassification,\u201d if we may reserve the honorable\nname of systematics for the rational type, is possible here, a mere\nstatement in the form of a catalogue, useful for orientation but for\nnothing more. We may classify all varieties of hats or of tables in the\nsame way.\n\n\nBIOLOGICAL SYSTEMATICS\n\nAt this point we return from our logical excursion to our proper subject\nof biology; for I am sorry to say biological systematics is at present\nof our second type of systematics throughout: it is classification pure\nand simple. We have a catalogue in our hands, but nothing more.\n\nSuch a statement of fact conveys not a particle of censure, casts not\nthe least reflection on the gifted men who created the classification of\nanimals or plants. It is absolutely necessary to have such a catalogue,\nand indeed the catalogue of the organisms can be said to have been\nimproved enormously during the advance of empirical and descriptive\nbiological science. Any classification improves as it becomes more\n\u201cnatural,\u201d as the different possible schemes of arrangement, the\ndifferent reasons of division, agree better and better in their results;\nand, in fact, there has been a great advance of organic classification\nin this direction. The \u201cnatural\u201d system has reached such perfection,\nthat what is related from one point of view seems nearly related also\nfrom almost all points of view which are applicable, at least from those\nwhich touch the most important characteristics. There has been a real\nweighing of all the possible reasons of division, and that has led to a\nresult which seems to be to some extent final.\n\nBut, nevertheless, we do not understand the *raison d\u2019\u00eatre* of the\nsystem of organisms; we are not at all able to say that there must be\nthese classes or orders or families and no others, and that they must be\nsuch as they are.\n\nShall we ever be able to understand that? Or will organic systematics\nalways remain empirical classification? We cannot answer this question.\nIf we could, indeed, we should have what we desire! As simple relations\nof space are certainly not the central point of any problematic rational\norganic systematics even of the future, the question arises, whether\nthere could be found any principle of another type in the realm of\nsynthetic *a priori* judgments which could allow an inherent sort of\nevolution of latent diversities, as do all judgments about spatial\nsymmetry. At the end of the second course of these lectures, which is to\nbe delivered next summer, we shall be able to say a few more words about\nthis important point.\n\nThe concept of what is called \u201ca type,\u201d due almost wholly to Cuvier and\nGoethe, is the most important of all that classification has given to\nus. Hardly second in importance is the discovery of the \u201ccorrelation of\nparts,\u201d as a sort of connection which has the character of necessity\nwithout being immediately based upon causality. R\u00e1dl seems to be\nthe only modern author who has laid some stress on this topic. The\nharmony which we have discovered in development is also part of this\ncorrelation. When, later on, we come to discuss analytically our well\nestablished entelechy as the ultimate basis of individual organisation,\nwe shall be able to gain more satisfactory ideas with respect to the\nmeaning of the non-causal but necessary connection, embraced in the\nconcepts of type and of correlation of parts.\n\nThe type is a sort of irreducible arrangement of different parts; the\ncorrelation deals with the degree and the quality of what may be called\nthe actual make of the parts, in relation to one another: all ruminants,\nfor instance, are cloven-footed, the so-called dental formulae are\ncharacteristic of whole groups of mammals. Of course all such statements\nare empirical and have their limits: but it is important that they are\npossible.[142]\n\n[142] Recent years have created the beginnings of a systematics based on\nchemical differences of metabolism and its products: such differences in\nfact have been found to go hand in hand with diversities of the type in\nsome cases (v. Bunge, Przibram, etc.).\n\nIt has been the chief result of comparative embryology to show that the\ntype as such is more clearly expressed in developmental stages than\nit is in the adults, and that therefore the embryological stages of\ndifferent groups may be very much more similar to each other than are\nthe adults: that is the truth contained in the so-called \u201cbiogenetisches\nGrundgesetz.\u201d But the specific differences of the species are not\nwanting in any case of ontogeny, in spite of such similarities in\ndifferent groups during development.\n\nWe have applied the name \u201csystematics\u201d or, if rationality is excluded,\n\u201cclassification\u201d to all that part of a science which deals with\ndiversities instead of generalities: in such a wide meaning systematics,\nof course, is not to be confused with that which is commonly called so\nin biology, and which describes only the exterior differences of form.\nOur systematics is one of the two chief parts of biology; what are\ncalled comparative anatomy and comparative embryology are its methods.\nFor it must be well understood that these branches of research are only\nmethods and are not sciences by themselves.\n\n\n\n\n*B.* THE THEORY OF DESCENT\n\n\n1. GENERALITIES\n\nIt is most generally conceded at the present time that the actually\nexisting state of all organisms whatsoever is the result of their\nhistory. What does that mean? What are the foundations upon which the\nassumption rests? What is the relation of systematics to history? In\nraising such questions and considerations we are treading the ground\nsacred to the theory of descent.\n\nI well know that you prefer the name \u201ctheory of evolution\u201d for what\nI am speaking of: but it may be misleading in various respects. We\nalready know that quite a determinate meaning has been given to the word\n\u201cevolutio\u201d as applied to individual morphogenesis, \u201cevolutio\u201d being\nhere opposed to \u201cepigenesis.\u201d Now there would be nothing against the\nuse of the word evolution in a wider sense--indeed it is often applied\nnowadays to denote the fact that a something is actually \u201cevolved\u201d in\nembryology--if only our entelechy had taken the place of the machine\nof the mechanists. But that is the very point: there must be a real\n\u201cevolving\u201d of a something, in order that the word evolution may be\njustified verbally: and that is not the case in so-called phylogeny. At\nleast we know nothing of an evolutionary character in the problematic\npedigree of the organisms, as we shall see more fully hereafter. The\nterm \u201ctheory of descent\u201d is therefore less open to objection than is the\nusual English term. The word transformism, as used by the French, would\nalso be a very good title.\n\nThe theory of descent is the hypothetic statement that the organisms\nare really allied by blood among each other, in spite of their\ndiversities.[143] The question about their so-called monophyletic\nor polyphyletic origin is of secondary importance compared with the\nstatement of relationship in general.\n\n[143] We prefer this unpretending definition of the theory of descent\nto every other. As soon as one introduces into the definition the\nconcept of the \u201ctransmutability of species,\u201d the term \u201cspecies\u201d would\nrequire a special definition, and that would lead to difficulties which\nit is unnecessary to deal with for our main purposes. It has been\nremarked by Kra\u0161an, (*Ausichten und Gespr\u00e4che \u00fcber die individuelle und\nspecifische Gestaltung in der Natur*) and by several other writers,\nthat the problem of mutability or immutability of course relates to the\nindividuals in the first place. I should like to add to this remark that\nthe possibility must be admitted of the individuals being transmutable,\nwhilst the \u201cspecies\u201d are not transmutable at the same time, the line\nof the \u201cspecies\u201d being a fixed order, through which the \u201cindividuals\u201d\nhave to pass in the course of their generations. What is meant here\nwill become clearer, when we study the different possible aspects of\n\u201cphylogeny.\u201d\n\nThere are two different groups of facts which have suggested the idea\nof transformism: none of these facts can be said to be conclusive, but\nthere certainly is a great amount of probability in the whole if taken\ntogether.\n\nThe first group of evidences which lead to the hypothesis of the real\nrelationship of organisms consists of facts relating to the geographical\ndistribution of animals and plants and to pal\u00e6ontology. As to geography,\nit seems to me that the results of the floral and faunal study of groups\nof islands are to be mentioned in the first place. If, indeed, on\neach of the different islands, *A* *B* *C* and *D*, forming a group,\nthe species of a certain genus of animals or plants are different in a\ncertain respect, and show differences also compared with the species\nliving on the neighbouring continent, of which there is geological\nevidence that the islands once formed a part, whilst there is no change\nin the species on the continent itself for very wide areas, then, no\ndoubt, the hypothesis that all these differing species once had a common\norigin, the hypothesis that there is a certain community among them all,\nwill serve to elucidate in some way what would seem to be very abstruse\nwithout it. And the same is true of the facts of palaeontology. In\nthe geological strata, forming a continuous series, you find a set of\nanimals, always typical and specific for every single stratigraphical\nhorizon, but forming a series just as do those horizons. Would not the\nwhole aspect of these facts lose very much of its peculiarity if you\nwere to introduce the hypothesis that the animals changed with the\nstrata? The continuity of life, at least, would be guaranteed by such an\nassumption.\n\nThe geographical and geological evidences in favour of the theory of\ndescent are facts taken from sciences which are not biology proper; they\nare not facts of the living but only facts about the living. That is not\nquite without logical importance, for it shows that not biology alone\nhas led to the transformism hypothesis. Were it otherwise, transformism\nmight be said to be a mere hypothesis *ad hoc*; but now this proves to\nbe not the case, though we are far from pretending that transformism\nmight be regarded as resting upon a real *causa vera*.\n\nBut let us study the second group of facts which support the theory of\ndescent. It is a group of evidences supplied by biology itself that we\nmeet here, there being indeed some features in biology which can be\nsaid to gain some light, some sort of elucidation, if the theory of\ndescent is accepted. Of course, these facts can only be such as relate\nto specific diversities, and indeed are facts of systematics; in other\nwords, there exists something in the very nature of the system of\norganisms that renders transformism probable. The system of animals and\nplants is based upon a principle which might be called the principle\nof *similarities and diversities by gradation*; its categories are not\nuniform but different in degree and importance, and there are different\nkinds of such differences. No doubt, some light would be shed upon this\ncharacter of the system, if we were allowed to assume that the relation\nbetween similarities and diversities, which is gradual, corresponded to\na blood-relationship, which is gradual also.\n\n\nTHE COVERT PRESUMPTION OF ALL THEORIES OF DESCENT\n\nWe have used very neutral and somewhat figurative words, in order to\nshow what might be called the logical value of the theory of descent,\nin order to signify its value with respect to so-called \u201cexplanation.\u201d\nWe have spoken of the \u201clight\u201d or the \u201celucidation\u201d which it brings, of\nthe \u201cpeculiarity of aspect\u201d which is destroyed by it. We have used this\nterminology intentionally, for it is very important to understand that\na specific though hidden addition is made almost unconsciously to the\nmere statement of the hypothesis of descent as such, whenever this\nhypothesis is advocated in order to bring light or elucidation into any\nfield of systematic facts. And this additional hypothesis indeed must be\nmade from the very beginning, quite irrespective of the more detailed\nproblems of the law of transformism, in order that *any* sort of\nso-called explanation by means of the theory of descent may be possible\nat all. Whenever the theory that, in spite of their diversities, the\norganisms are related by blood, is to be really useful for explanation,\nit must necessarily be assumed in every case that the steps of change,\nwhich have led the specific form *A* to become the specific form *B*,\nhave been such as only to change *in part* that original form *A*. That\nis to say: the similarities between *A* and *B* must never have become\novershadowed by their diversities.\n\nOnly on this assumption, which indeed is a newly formed additional\nsubsidiary hypothesis, joined to the original hypothesis of descent in\ngeneral--a hypothesis regarding the very nature of transformism--only\non this almost hidden assumption is it possible to speak of any sort of\n\u201cexplanation\u201d which might be offered by the theory of transformism to\nthe facts of geography, geology, and biological systematics. Later on\nwe shall study more deeply the logical nature of this \u201cexplanation\u201d; at\npresent it must be enough to understand this term in its quasi-popular\nmeaning.\n\nWhat is explained by the hypothesis of descent--including the additional\nhypothesis, that there always is a prevalence of the similarities\nduring transformism--is the fact that in palaeontology, in the groups\nof island and continent faunae and florae taken as a whole, as well as\nin the single categories of the system, the similarities exceed the\ndiversities. The *similarities* now are \u201cexplained\u201d; that is to say,\nthey are understood as resting on but one principle: the similarities\nare understood as being due to inheritance;[144] and now we have but one\nproblem instead of an indefinite number. For this reason Wigand granted\nthat the theory of descent affords what he calls a numerical reduction\nof problems.\n\n[144] It seems to me that my argument gives a broader logical basis\nto the theory of descent than does that of G. Wolff (*Die Begr\u00fcndung\nder Abstammungslehre*, M\u00fcnchen, 1907). Wolff starts from the concept\nof organic teleology, and thus finds the only reason for accepting\nthe theory of transformism in the existence of so-called \u201crudimentary\norgans\u201d; these organs would form an obstacle to teleology if they could\nnot be regarded as inherited.\n\nUnderstanding then what is explained by the theory of descent with its\nnecessary appendix, we also understand at once what is *not* elucidated\nby it: the diversities of the organism remain as unintelligible as they\nalways were, even if we know that inheritance is responsible for what\nis similar or equal. Now there can be no doubt that the diversities are\nthe more important point in systematics; if there were only similarities\nthere would be no problem of systematics, for there would be no system.\nLet us be glad that there are similarities in the diversities, and that\nthese similarities have been explained in some way; but let us never\nforget what is still awaiting its explanation. Unfortunately it has been\nforgotten far too often.\n\n\nTHE SMALL VALUE OF PURE PHYLOGENY\n\nAnd so we are led to the negative side of the theory of transformism,\nafter having discussed its positive half. The theory of descent as\nsuch, without a real knowledge of the factors which are concerned in\ntransformism, or of the law of transformism, in other terms, leaves the\nproblem of systematics practically where it was, and adds really nothing\nto its solution. That may seem very deplorable, but it is true.\n\nImagine so-called historical geology, without any knowledge of the\nphysical and chemical factors which are concerned in it: what would\nyou have except a series of facts absolutely unintelligible to you? Or\nsuppose that some one stated the cosmogenetic theory of Kant and Laplace\nwithout there being any science of mechanics: what would the theory mean\nto you? Or suppose that the whole history of mankind was revealed to\nyou, but that you had absolutely no knowledge of psychology: what would\nyou have but facts and facts and facts again, with not a morsel of real\nexplanation?\n\nBut such is the condition in which so-called phylogeny stands. If it\nis based only on the pure theory of transformism, there is nothing\nexplained at all. It was for this reason that the philosopher Liebmann\ncomplained of phylogeny that it furnishes nothing but a \u201cgallery of\nancestors.\u201d And this gallery of ancestors set up in phylogeny is not\neven certain; on the contrary, it is absolutely uncertain, and very\nfar from being a fact. For there is no sound and rational principle\nunderlying phylogeny; there is mere fantastic speculation. How could it\nbe otherwise where all is based upon suppositions which themselves have\nno leading principle at present? I should not like to be misunderstood\nin my polemics against phylogeny. I fully grant you that it may be\npossible in a few cases to find out the phylogenetic history of smaller\ngroups with some probability, if there is some palaeontological\nevidence in support of pure comparative anatomy; and I also do not\nhesitate to allow that such a statement would be of a certain value with\nregard to a future discovery of the \u201claws\u201d of descent, especially if\ntaken together with the few facts known about mutations. But it is quite\nanother thing with phylogeny on the larger scale. Far more eloquent than\nany amount of polemics is the fact that vertebrates, for instance, have\nalready been \u201cproved\u201d to be descended from, firstly, the amphioxus;\nsecondly, the annelids; thirdly, the *Sagitta* type of worms; fourthly,\nfrom spiders; fifthly, from *Limulus*, a group of crayfishes; and\nsixthly, from echinoderm larvae. That is the extent of my acquaintance\nwith the literature, with which I do not pretend to be specially\nfamiliar. Emil du Bois-Reymond said once that phylogeny of this sort is\nof about as much scientific value as are the pedigrees of the heroes of\nHomer, and I think we may fully endorse his opinion on this point.\n\n\nHISTORY AND SYSTEMATICS\n\nA few words should be devoted to the relations between history and\nsystematics in biology. Is there no contradiction between historical\ndevelopment and a true and rational system which, we conceded, might\nexist some day in biological sciences, even though it does not at\npresent? By no means. A totality of diversities is regarded from quite\ndifferent points of view if taken as the material of a system, and if\nconsidered as realised in time. We have said that chemistry has come\nvery near to proper rational systematics, at least in some of its\nspecial fields; but the compounds it deals with at the same time may\nbe said to have originated historically also, though not, of course,\nby a process of propagation. It is evident at once that the geological\nconditions of very early times prohibited the existence of certain\nchemical compounds, both organic and inorganic, which are known at\npresent. None the less these compounds occupy their proper place in\nthe system. And there may be many substances theoretically known to\nchemical systematics which have never yet been produced, on account\nof the impossibility of arranging for their proper conditions of\nappearance, and nevertheless they must be said to \u201cexist.\u201d \u201cExistence,\u201d\nas understood in systematics, is independent of special space and of\nspecial time, as is the existence of the laws of nature: we may speak of\na Platonic kind of existence here. Of course it does not contradict this\nsort of ideal existence if reality proper is added to it.\n\nThus the problem of systematics remains, no matter whether the theory\nof descent be right or wrong. There always remains the question about\nthe totality of diversities in life: whether it may be understood by\na general principle, and of what kind that principle would be. As,\nin fact, it is most probably by history, by descent, that organic\nsystematics is brought about, it of course most probably will happen\nsome day that the analysis of the causal factors concerned in the\nhistory will serve to discover the principle of systematics also.\n\nLet us now glance at the different kinds of hypotheses which have been\nestablished in order to explain how the descent of the organisms might\nhave been possible. We have seen that the theory of transformism alone\nis not worth very much as a whole, unless at least a hypothetical\npicture can be formed of the nature of the transforming factors: it is\nby some such reasoning that almost every author who has defended the\ntheory of descent in its universality tries to account for the manner in\nwhich organisms have acquired their present diversities.\n\n\n2. THE PRINCIPLES OF DARWINISM\n\nThere is no need in our times and particularly in this country, to\nexplain in a full manner the theory known under the name of Darwinism.\nAll of you know this theory, at least in its outlines, and so we may\nenter at once upon its analytic discussion. A few words only I beg\nyou to allow me as to the name of \u201cDarwinism\u201d itself. Strange to say,\nDarwinism, and the opinion of Charles Darwin about the descent of\norganisms, are two different things. Darwin, the very type of a man\ndevoted to science alone and not to personal interests,--Darwin was\nanything but dogmatic, and yet Darwinism is dogmatism in one of its\npurest forms. Darwin, for instance, gave the greatest latitude to the\nnature of the variations which form the battleground of the struggle\nfor existence and natural selection; and he made great allowances for\nother causal combinations also, which may come into account besides\nthe indirect factors of transformism. He was Lamarckian to a very\nfar-reaching extent. And he had no definite opinion about the origin\nand the most intimate nature of life in general. These may seem to\nbe defects but really are advantages of his theory. He left open the\nquestion which he could not answer, and, in fact, he may be said to be a\ngood illustration of what Lessing says, that it is not the possession\nof truth but the searching after it, that gives happiness to man. It was\nbut an outcome of this mental condition that Darwin\u2019s polemics never\nleft the path of true scientific discussions, that he never in all his\nlife abused any one who found reason to combat his hypotheses, and that\nhe never turned a logical problem into a question of morality.\n\nHow different is this from what many of Darwin\u2019s followers have made out\nof his doctrines, especially in Germany; how far is \u201cDarwinism\u201d removed\nfrom Darwin\u2019s own teaching and character!\n\nIt is to Darwinism of the *dogmatic* kind, however, that our next\ndiscussions are to relate, for, thanks to its dogmatism, it has the\nadvantage of allowing the very sharp formulation of a few causal\nfactors, which *a priori* might be thought to be concerned in organic\ntransformism, though we are bound to say that a really searching\nanalysis of these factors ought to have led to their rejection from the\nvery beginning.\n\nThe logical structure of dogmatic Darwinism reveals two different parts,\nwhich have nothing at all to do with one another.\n\n\nNATURAL SELECTION\n\nWe shall first study that part of it which is known under the title\nof natural selection, irrespective of the nature of the causes of\nprimary differences, or, in other words, the nature of variability.\nThis part may be said to belong to Darwin\u2019s personal teachings and not\nonly to \u201cDarwinism.\u201d The offspring of a certain number of adults show\ndifferences compared with each other; there are more individuals in the\noffspring than can grow up under the given conditions, therefore there\nwill be a struggle for existence amongst them, which only the fittest\nwill survive; these survivors may be said to have been \u201cselected\u201d by\nnatural means.\n\nIt must be certain from the very beginning of analysis that natural\nselection, as defined here, can only eliminate what cannot survive, what\ncannot stand the environment in the broadest sense, but that natural\nselection never is able to create diversities. It always acts negatively\nonly, never positively. And therefore it can \u201cexplain\u201d--if you will\nallow me to make use of this ambiguous word--it can \u201cexplain\u201d only why\ncertain types of organic specifications, imaginable *a priori*, do\n*not* actually exist, but it never explains at all the existence of the\nspecifications of animal and vegetable forms that are actually found. In\nspeaking of an \u201cexplanation\u201d of the origin of the living specific forms\nby natural selection one therefore confuses the sufficient reason for\nthe non-existence of what there is not, with the sufficient reason for\nthe existence of what there is. To say that a man has explained some\norganic character by natural selection is, in the words of N\u00e4geli, the\nsame as if some one who is asked the question, \u201cWhy is this tree covered\nwith these leaves,\u201d were to answer \u201cBecause the gardener did not cut\nthem away.\u201d Of course that would explain why there are no more leaves\nthan those actually there, but it never would account for the existence\nand nature of the existing leaves as such. Or do we understand in the\nleast why there are white bears in the Polar Regions if we are told that\nbears of other colours could not survive?\n\nIn denying any real explanatory value to the concept of natural\nselection I am far from denying the action of natural selection. On\nthe contrary, natural selection, to some degree, is *self-evident*;\nat least as far as it simply states that what is incompatible with\npermanent existence cannot exist permanently, it being granted that\nthe originating of organic individuals is not in itself a guarantee of\npermanency. Chemical compounds, indeed, which decompose very rapidly\nunder the conditions existing at the time when they originated may also\nbe said to have been eliminated by \u201cnatural selection.\u201d It is another\nquestion, of course, whether in fact all eliminations among organic\ndiversities are exclusively due to the action of natural selection in\nthe proper Darwinian sense. It has been pointed out already by several\ncritics of Darwinism and most clearly by Gustav Wolff, that there are\nmany cases in which an advantage with regard to situation will greatly\noutweigh any advantage in organisation or physiology. In a railway\naccident, for instance, the passengers that survive are not those who\nhave the strongest bones, but those who occupied the best seats; and\nthe eliminating effect of epidemics is determined at least as much by\nlocalities, *e.g.* special houses or special streets, as by the degree\nof immunity. But, certainly, natural selection is a *causa vera* in many\nother cases.\n\nWe now may sum up our discussion of the first half of Darwinism.\nNatural selection is a negative, an eliminating factor in transformism;\nits action is self-evident to a very large degree, for it simply\nstates that things do not exist if their continuance under the given\nconditions is impossible. To consider natural selection as a positive\nfactor in descent would be to confound the sufficient reason for the\nnon-existence of what is not, with the sufficient reason of what is.\n\nNatural selection has a certain important logical bearing on\nsystematics, as a science of the future, which has scarcely ever been\nalluded to. Systematics of course has to deal with the totality of the\npossible, not only of the actual diversities; it therefore must remember\nthat more forms may be possible than are actual, the word \u201cpossible\u201d\nhaving reference in this connection to originating, not to surviving.\nMoreover, systematics is concerned not only with what has been\neliminated by selection, but also with all that might have originated\nfrom the eliminated types. By such reasoning natural selection gains a\nvery important aspect--but a logical aspect only.\n\n\nFLUCTUATING VARIATION THE ALLEGED CAUSE OF ORGANIC DIVERSITY\n\nThe second doctrine of dogmatic Darwinism states that all the given\ndiversities among the organisms that natural selection has to work\nupon are offered to natural selection by so-called fluctuating\nvariation; that is, by variation as studied by means of statistics.\nThis sort of variation, indeed, is maintained to be indefinite in\ndirection and amount, at least by the most conservative Darwinians; it\nhas occasionally been called a real differential; in any case it is\nlooked upon as being throughout contingent with regard to some unity\nor totality; which, of course, is not to mean that it has not had a\nsufficient reason for occurring.\n\nIt could hardly be said to be beyond the realm of possibility that such\ndifferences among organic species as only relate to degree or quantity\nand perhaps to numerical conditions also, might have been \u201cselected\u201d out\nof given contingent variations, if but one postulate could be regarded\nas fulfilled. This postulate may appropriately be stated as the fixation\nof new averages of variation by inheritance. Let the average value of\na variation, with regard to a given property of a given species be *n*\nand let the value *n* + *m*--*m* being variable--which is represented in\nfewer individuals of course than is *n*, be such as to offer advantages\nin the struggle for existence; then the individuals marked by *n* + *m*\nwill have the greater chance of surviving. Our postulate now states\nthat, in order that a permanent increase of the average value of the\nvariation in question may be reached, *n* + *m* in any of its variable\nforms must be able to become the average value of the second generation,\nas *n* was the average value of the first. Out of the second generation\nagain it would be the few individuals marked by *n* + *m* + *o*, which\nwould be selected; *n* + *m* + *o* would be the new average; afterwards\n*n* + *m* + *o* + *p* would be selected, would become the new average,\nand so on. A black variety for instance might be selected by such a\nseries of processes out of a grey-coloured one without difficulty.\n\nBut our postulate is not beyond all doubt: certain experiments, at\nleast, which have been carried out about the summation of variations\nof the true fluctuating type by any kind of selection seem to show\nthat there may be a real progress for a few generations, but that this\nprogress is always followed by a reversion. Of course our experience\nis by no means complete on this subject, and, indeed, it may be shown\nin the future that positive transforming effects of fluctuating\nvariability, in connection with selective principles, are possible in\nthe case of new quantitative differences (in the widest sense), but we\nare not entitled to say so at present.\n\nAnd this is the only condition on which we can give credit to the second\ndoctrine of dogmatic Darwinism. Its second principle, indeed, proves\nto be absolutely inadequate to explain the origin of any other kind of\nspecific properties whatever.\n\nI cannot enter here into the whole subject of Darwinian criticism.[145]\nOur aims are of a positive character, they desiderate construction\nand only use destruction where it is not to be avoided. So I shall\nonly mention that dogmatic Darwinism has been found to be unable to\nexplain every kind of mutual adaptations, *e.g.* those existing between\nplants and insects; that it can never account for the origin of those\nproperties that are indifferent to the life of their bearer, being mere\nfeatures of organisation as an arrangement of parts; that it fails in\nthe face of all portions of organisation which are composed of many\ndifferent parts--like the eye--and nevertheless are functional units\nin any passive or active way; and that, last not least, it has been\nfound to be quite inadequate to explain the first origin of all newly\nformed constituents of organisation even if they are not indifferent:\nfor how could any rudiment of an organ, which is not functioning at all,\nnot only be useful to its bearer, but be useful in such a degree as to\ndecide about life or death?\n\n[145] See Wigand, *Der Darwinismus und die Naturforschung Newton\u2019s und\nCuvier\u2019s*, Braunschweig, 1874-7; N\u00e4geli, *Mechanisch-physiologische\nTheorie der Abstammungslehre*, M\u00fcnchen, 1884; G. Wolff, *Beitr\u00e4ge zur\nKritik der Darwin\u2019schen Lehre*, 2nd ed. Leipzig, 1898; etc.\n\nIt is only for one special feature that I should like to show, by\na more full analysis, that dogmatic Darwinism does not satisfy the\nrequirements of the case. The special strength of Darwinism is said to\nlie in its explaining everything that is useful in and for organisms;\nthe competitive factor it introduces does indeed seem to secure at least\na relative sort of adaptedness between the organism and its needs. But\nin spite of that, we shall now see that Darwinism fails absolutely to\nexplain those most intimate organic phenomena which may be said to be\nthe most useful of all.\n\nDarwinism in its dogmatic form is not able to explain the origin of any\nsort of organic restitution; it is altogether impossible to account for\nthe restitutive power of organisms by the simple means of fluctuating\nvariation and natural selection in the struggle for existence. Here we\nhave the logical *experimentum crucis* of Darwinism.\n\nLet us try to study in the Darwinian style the origin of the\nregenerative faculty, as shown in the restitution of the leg of a\nnewt. All individuals of a given species of the newt, say *Triton\ntaeniatus*, are endowed with this faculty; all of them therefore must\nhave originated from ancestors which acquired it at some time or other.\nBut this necessary supposition implies that all of these ancestors must\nhave lost their legs in some way, and not only one, but all four of\nthem, as they could not have acquired the restitutive faculty otherwise.\nWe are thus met at the very beginning of our argument by what must be\ncalled a real absurdity, which is hardly lessened by the assumption that\nregeneration was acquired not by all four legs together, but by one\nafter the other. But it is absolutely inevitable to assume that *all*\nthe ancestors of our *Triton* must have lost one leg, or more correctly,\nthat only those of them survived which had lost one! Otherwise not all\nnewts at the present day could possess the faculty of regeneration! But\na second absurdity follows the first one; out of the ancestors of our\nnewt, which survived the others by reason of having lost one of their\nlegs, there were selected only those which showed at least a very small\namount of healing of their wound. It must be granted that such a step\nin the process of selection, taken by itself, would not at all seem to\nbe impossible; since healing of wounds protects the animals against\ninfection. But the process continues. In every succeeding stage of it\nthere must have survived only those individuals which formed just a\nlittle more of granulative tissue than did the rest: though *neither*\nthey themselves *nor* the rest could use the leg, which indeed was\nnot present! That is the second absurdity we meet in our attempt at a\nDarwinian explanation of the faculty of regeneration; but I believe the\nfirst one alone was sufficient.\n\nIf we were to study the \u201cselection\u201d of the faculty of one of the\nisolated blastomeres of the egg of the sea-urchin to form a whole larva\nonly of smaller size, the absurdities would increase. At the very\nbeginning we should encounter the absurdity, that of all the individuals\nthere survived only those which were not whole but half; for *all*\nsea-urchins are capable of the ontogenetical restitution in question,\n*all* of their ancestors therefore must have acquired it, and they\ncould do that only *if* they became halved at first by some accident\nduring early embryology. But we shall not insist any further on this\ninstance, for it would not be fair to turn into ridicule a theory which\nbears the name of a man who is not at all responsible for its dogmatic\nform. Indeed, we are speaking against Darwinism of the most dogmatic\nform only, not against Darwin himself. He never analysed the phenomena\nof regeneration or of embryonic restitution--they lay in a field very\nunfamiliar to him and to his time. I venture to say that if he had taken\nthem into consideration, he would have agreed with us in stating that\nhis theory was not at all able to cover them; for he was prepared to\nmake great concessions, to Lamarckism for instance, in other branches of\nbiology, and he did not pretend, to know what life itself is.\n\nDarwin was not a decided materialist, though materialism has made\ngreat capital out of his doctrines, especially in Germany. His book,\nas is well known, is entitled \u201cThe Origin of *Species*,\u201d that is of\norganic *diversities*, and he himself possibly might have regarded all\nrestitution as belonging to the original properties of life, anterior to\nthe originating of diversities. Personally he might possibly be called\neven a vitalist. Thus dogmatic \u201cDarwinism\u201d in fact is driven into all\nthe absurdities mentioned above, whilst the \u201cdoctrine of Darwin\u201d can\nonly be said to be wrong on account of its failing to explain mutual\nadaptation, the origin of new organs, and some other features in organic\ndiversities; the original properties of life were left unexplained by it\nintentionally.\n\n\nDARWINISM FAILS ALL ALONG THE LINE\n\nThe result of our discussion then must be this: selection has proved to\nbe a negative factor only, and fluctuating variation as the only way\nin which new properties of the organisms might have arisen has proved\nto fail in the most marked manner, except perhaps for a few merely\nquantitative instances. Such a result betokens the complete collapse\nof dogmatic Darwinism as a general theory of descent: the most typical\nfeatures of all organisms remain as unexplained as ever.\n\nWhat then shall we put in the place of pure Darwinism? Let us first try\na method of explanation which was also adopted occasionally by Darwin\nhimself: let us study that form of transformation theories which is\ncommonly known under the title of Lamarckism.\n\n\n3. THE PRINCIPLES OF LAMARCKISM.\n\nAs the word \u201cDarwinism\u201d does not signify the proper theoretical system\nof Charles Darwin, so Lamarckism as commonly understood nowadays is a\ngood deal removed from the original views of Jean Baptiste Lamarck.\nLamarckism is generally regarded as reducing all organic diversities to\ndifferences in the needs of individual life, but Lamarck himself, as\nmust be emphasised from the very beginning, did not at all maintain the\nopinion that the great characteristics of the types were only due to\nsuch accidental factors. He supposed a sort of law of organisation to\nbe at the root of systematics, as developed in history, and the needs\nof life were only responsible, according to him, for splitting the\ngiven types of organisation into their ultimate branches. Thus Lamarck,\nto a great extent at any rate, belongs to a group of authors that we\nshall have to study afterwards: authors who regard an unknown law of\nphylogenetic development as the real basis of transformism. Modern\nso-called Neo-Lamarckism, on the other hand, has indeed conceded the\nprinciple of needs to be the sole principle of transformism. Let us then\nstudy Lamarckism in its dogmatic modern form.\n\n\nADAPTATION AS THE STARTING-POINT\n\nAll facts of morphological adaptations--facts which we have analysed\nalready from a different point of view, as being among the most typical\nphenomena of organic regulation--form the starting-point of this\ntheory, and it must be granted that they form a very solid foundation,\nfor they are facts. The theory only has to enlarge hypothetically the\nrealm of these facts, or rather the realm of the law that governs them.\nIndeed, it is assumed by Lamarckism that the organism is endowed with\nthe faculty of responding to *any* change of the environment which may\nchange its function by a morphologically expressed alteration of its\nfunctional state and form, which is adapted to the state of conditions\nimposed from without. Of course, as stated in this most general form,\nthe assumption is not true, but it is true within certain limits, as\nwe know; and there seems to be no reason why we should not believe\nthat there are many more cases of adaptation than we actually know at\npresent, or that, in former phylogenetic times, the organisms were more\ncapable of active adaptation than they are now. So to a certain extent,\nat least, Lamarckism can be said to rest upon a *causa vera*.\n\nIt is important to notice that this *causa vera* would imply vitalistic\ncausality when taken in the wide meaning which Lamarckism allows to\nit: indeed, the power of active adaptation to indefinite changes would\nimply a sort of causal connection that is nowhere known except in the\norganism. Lamarck himself is not very clear about this point, he seems\nto be afraid of certain types of uncritical vitalism in vogue in his\ndays; but modern writers have most clearly seen what the logical\nassumptions of pure Lamarckism are. Next to Cope, August Pauly[146] may\nbe said to be the most conscious representative of a sort of so-called\npsychological vitalism, which indeed Lamarckism as a general and\nall-embracing theory must have as its basis.\n\n[146] *Darwinismus und Lamarckismus*, M\u00fcnchen, 1905.\n\n\nTHE ACTIVE STORING OF CONTINGENT VARIATIONS AS A HYPOTHETIC PRINCIPLE\n\nThis point will come out more fully, if now we turn to study a certain\ngroup of principles, upon which dogmatic Lamarckism rests: I say\nprinciples and not facts, for there are no facts but only hypothetic\nassumptions in this group of statements. We do know a little about\nadaptations, at least to a certain extent, and it was only about the\nsphere of the validity of a law, which was known to be at work in\ncertain cases, that hypothetical additions were made. In the second\ngroup of the foundations of Lamarckism we know absolutely nothing;\naccidental variations of form are supposed to occur, and the organism is\nsaid to possess the faculty of keeping and storing these variations and\nof handing them down to the next generation, if they happen to satisfy\nany of its needs.\n\nBut these needs are not of the actual type, brought forth by a change of\nthe functional state of the individual, as in the case of adaptations:\nthey are of a somewhat mysterious nature. A glance at the theory of the\norigin of the movements which are called acts of volition in the human\nchild may serve to elucidate what is meant.\n\nActs of volition are said thus to originate in random movements of the\nnew-born infant: certain of these accidental motions which happen to\nrelieve some pain or to afford some pleasure are \u201cremembered,\u201d and are\nused another time quite consciously to bring forth what is liked or to\nremove what is disliked. So much for the present on a very difficult\nsubject, which will occupy us next year at much greater length. It is\nclear that at least three fundamental phenomena are concerned in this\ntheory of the origin of acts of volition: the liking and disliking, the\nkeeping in mind, and the volition itself. The real act of volition,\nindeed, is always based upon a connection of all these factors, these\nfactors now being connected in such a way that even their kind of\nconnection may be said to be a fourth fundamental principle. In order\nthat the particular effect may be obtained which is wanted because it is\nliked, the possible ways leading to it, which appeared among the random\nmovements in the very beginning, are now regarded as \u201cmeans\u201d and may now\nbe said to be \u201cused.\u201d But that is as much as to say that the \u201cmeans\u201d\nare judged with respect to their usefulness for the actual purpose, and\ntherefore *judgment* is the fourth foundation of the act of volition.\n\nIn fact, Pauly does not hesitate to attribute judgment, along with the\nother psychological elements, to the organisms whilst undergoing their\ntransformation. There has been formed, for instance, by accidental\nvariation some pigment which by its chemical nature brings the organism\ninto a closer connection with the light of the medium; the individual\nlikes that, keeps the pigment for itself and produces it again in the\nnext generation; and indeed it will safeguard any sort of improvement\nwhich chance may effect in this primitive \u201ceye.\u201d Such a view is said\nto hold well with respect to the origin of every new organ. And this\npsychological argument is also said to afford the real explanation of\nadaptation proper. Adaptation also is regarded not as a truly primary\nfaculty of the organism, but as a retention or provoking of metabolic\nstates which occurred by accident originally and were then found to\nbe useful; now they are reproduced either in every single case of\nindividual morphogenesis, without regard to actual requirements, or\nelse only in response to such: in the first case they are \u201cinherited,\u201d\nin the second they only occur as regulations. Thus the process of\njudgment, together with all the other elemental factors of psychical\nlife concerned in it, has been made to account for adaptation proper.\nThe whole theory has accordingly become very uniform and simple.\n\n\nCRITICISM OF THE \u201cINHERITANCE OF ACQUIRED CHARACTERS\u201d ASSUMED BY\nLAMARCKISM\n\nIn addressing ourselves to the criticism of Neo-Lamarckism we shall\nneglect as far as possible all the different psychological principles\nconcerned in it--which in any case would need rather a great amount of\nepistemological sifting--and shall keep to those hypothetic facts which\nare supposed to be such as may be actually observed in nature.\n\nAll of you know that the so-called inheritance of acquired characters\nlies at the root of Lamarckism; and from this hypothesis our critical\nanalysis is to start, disregarding a larger or smaller number of\npsychological principles that are brought into the field.\n\nThe name of \u201cacquired characters\u201d may *a priori* be given to three\ndifferent types of phenomena: firstly, variations including mutations;\nsecondly, disease or injuries; and thirdly, the results of the actual\nprocess of adaptation of every kind.\n\nIn the first of these groups, the true problem of the inheritance of\n\u201cacquired\u201d characters appears only with certain restrictions. All\nvariations and mutations are indeed \u201cacquired\u201d by one generation so\nfar as the earlier generation did not possess them, but mutations, at\nleast, cannot be said to be acquired by the actual adult personality:\nthey are innate in it from its very beginning, and therefore may better\nbe called congenital.[147] Congenital properties of the mutation type\nare, in fact, known to be inherited: their inheritance does not present\nany problem of its own, but is included in the changes of the hereditary\ncondition to which they are due altogether.[148] All properties of the\nvariation type, on the other hand, having been studied statistically,\nare known to be inherited, to a certain small extent, as we have seen\nalready whilst studying Darwinism, though they are possibly always\nliable to reversion. Modern science, as we know,[149] regards them as\ndue to changes of nutrition, in the most general meaning of the word.\nUnder such a view variations might indeed be said to belong to the\nacquired group of organic specifications; their inheritance, as will\nbe seen later on, would hardly be quite a pure instance of what we are\nsearching for. In no case can true variations claim to be of great\nimportance in problems of transformism.\n\n[147] This would not be true, if the varieties of plants produced by\nBlaringhem, Klebs, and MacDougal by means of *external* agents were\nreally \u201cmutations\u201d (comp. page 238, note 3).\n\n[148] Of course, the inheritance of mutations would imply a certain sort\nof \u201cinheritance of acquired characters,\u201d on the condition stated in the\npreceding note. But, probably, the germs of the next generation might\nbe regarded here as being directly affected by the external agent, in a\nmanner that will briefly be mentioned later on in the text.\n\n[149] Comp. page 238, note 2.\n\nBut what is known about the inheritance of those properties which\nbeyond any doubt may be said to have originated in the adult individual\nas such, and of which lesions and adaptations proper, as shown for\ninstance among amphibious plants, are instances of the two most\ntypical groups?[150] Weismann did good service by putting an end to\nthe scientific credulity which prevailed with regard to this subject.\nWeismann was led by his theory of the germ plasm to deny the inheritance\nof acquired characters of the typical kinds. He could not imagine how\nthe effect of any agent upon the adult, be it of the merely passive or\nof the adaptive kind, could have such an influence upon the germ as to\nforce it to produce the same effect in spite of the absence of that\nagent. In fact, that is what the inheritance of acquired characters\nwould render necessary, and a very strange phenomenon it would be,\nno doubt. But, of course, taken alone, it could never be a decisive\nargument against such inheritance. I fully agree, that science is\nobliged to explain new facts by what is known already, as long as it is\npossible; but if it is no longer possible, the theory of course has to\nbe changed, and not the facts. On this principle one would not neglect\nthe fact of an inheritance of acquired properties, but on the contrary\none perhaps might use it as a new evidence of vitalism.\n\n[150] Certain English authors have applied the term \u201cmodification\u201d to\nall kinds of organic properties acquired from without, whether they are\nadapted or not.\n\nBut are there any facts?\n\nAt this point we come to speak about the second group of Weismann\u2019s\nreasonings. He not only saw the difficulty of understanding inheritance\nof acquired characters on the principles of the science of his time,\nbut he also criticised the supposed facts; and scarcely any of them\nstood the test of his criticism. Indeed, it must fairly be granted that\nnot one case is known which really proves the inheritance of acquired\ncharacters, and that injuries certainly are never found to be inherited.\nIn spite of that, I do not believe that we are entitled to deny the\npossibility of the inheritance of a certain group of acquired characters\nin an absolute and dogmatic manner, for there are a few facts which seem\nat least to tend in the direction of such an inheritance, and which seem\nto show that it might be discovered perhaps one day, if the experimental\nconditions were changed.\n\nI am not referring here to the few cases in which bacteria were made\ncolourless or non-virulent by outside factors, or in which certain\nfungi were forced to permanent agamic reproduction by abnormal external\nconditions and were shown to retain their \u201cacquired properties\u201d\nafter the external conditions had been restored. In these cases only\nreproduction by simple division occurred, and that does not imply the\ntrue problem of inheritance. Nor am I referring to the few cases of\nnon-adaptive \u201cmodifications\u201d found by Standfuss and Fischer, in which\nbutterflies that had assumed an abnormal kind of pigmentation under\nthe influence of abnormal temperature acting upon the pupa, were seen\nto form this same kind of pigmentation in the next generation under\nnormal conditions of temperature. These cases, though important in\nthemselves, are capable perhaps of a rather simple explanation, as in\nfact has been suggested. Some necessary means both of inheritance and of\nmorphogenesis, the former being present in the propagation cells, may\nbe said to have been changed or destroyed by heat, and therefore, what\nseems to be inherited after the change of the body only, would actually\nbe the effect of a direct influence of the temperature upon the germ\nitself.[151] Let me be clearly understood: I do not say that it is so,\nbut it may be so. What seems to me to be more important than everything\nand to have a direct bearing on the real discovery of the inheritance\nof acquired characters in the future, is this. In some instances\nplants which had been forced from without to undergo certain typical\nmorphological adaptations, or at least changes through many generations,\nthough they did not keep the acquired characters permanently in spite\nof the conditions being changed to another type, were yet found to lose\nthe acquired adaptations not suddenly but only in the course of three\nor more generations. A certain fern, *Adiantum*, is known to assume a\nvery typical modification of form and structure, if grown on serpentine;\nnow Sadebeck,[152] while cultivating this serpentine modification of\n*Adiantum* on ordinary ground, found that the first generation grown in\nthe ordinary conditions loses only a little of its typical serpentine\ncharacter, and that the next generation loses a little more, so that\nit is not before the fifth generation that all the characters of the\nserpentine modification have disappeared. There are a few more cases\nof a similar type relating to plants grown in the plains or on the\nmountains. There also it was found to take time, or rather to take the\ncourse of *several* generations, until what was required by the new\nconditions was reached. Of course these cases are very very few compared\nwith those in which a *sudden* change of the adaptive character,\ncorresponding to the actual conditions, sets in; but it is enough that\nthey do exist.\n\n[151] Of course the inheritance of specific values from the results of\nfluctuating variations, leading to new averages of variability (see\np. 265), may also be understood in this manner, the conditions of\nnourishment acting upon the adult and upon its germs equally well.\n\n[152] *Berichte \u00fcb. d. Sitzung. d. Ges. f. Bot.*, Hamburg, 1887, 3 Heft.\n\nWould it not be possible at least that adaptations which last\nfor thousands of generations or more might in fact change the\nadaptive character into a congenital one? Then we not only should\nhave inheritance of acquired characters, but should have a sort\nof explanation at the same time for the remarkable fact that\ncertain histological structures of a very adapted kind are formed\nontogenetically before any function exists, as is known to be the\ncase with the structures in the bones of vertebrates, for instance.\nExperiments are going on at Paris, and perhaps in other places of\nscientific research also, which, it is hoped, will show that animals\nreared in absolute darkness for many generations will lose their\nperfectly formed eyes, and that animals from the dark with very\nrudimentary eyes will be endowed with properly functioning ones, after\nthey have been reared in the light for generations. Such a result indeed\nwould account for the many animals, of the most different groups, which\nlive in dark caves and possess only rudiments of eyes: functional\nadaptation is no longer necessary, so-called atrophy by inactivity sets\nin, and the results \u201cacquired\u201d by it are inherited.[153]\n\n[153] Quite recently Kammerer (*Arch. Entw. Mech.* 25, 1907, p. 7) has\npublished very important experiments on the inheritance of \u201cacquired\u201d\nmodifications with regard to the peculiarities of reproduction in\n*Salamandra atra* and *S. maculosa*. It seems rather improbable--though\nnot absolutely impossible--that the germ cells were directly affected by\nthe external modifying agent in this case.\n\nBut enough of possibilities. Let us be content at present to know at\nleast a few real instances with regard to the slowness of the process of\nwhat might be said to be \u201cre-adaptation\u201d in some plants. This process\nshows us a way by which our problem may some day be solved; it allows\nus to introduce inheritance of acquired characters as a legitimate\nhypothesis at least, which not only will explain many of the diversities\nin systematics historically, but also can be called, though not a *causa\nvera*, yet certainly more than a mere fiction.\n\n\nOTHER PRINCIPLES WANTED\n\nWe have only dealt with the probability of the inheritance of\nmorphological or physiological[154] adaptation. If that could really be\nconsidered as one of the factors concerned in the theory of descent,\nmany, if not all of those congenital diversities among organic species\nwhich are of the type of a true structural correspondence to their\nfuture functional life, might be regarded as explained, that is,\nas reduced to one and the same principle. But nothing more than an\nexplanation of *this* kind of diversities is effected by our principle,\nand very much more remains to be done, for organic diversities not only\nconsist in specifications and differences as to histology, but are to a\nmuch more important degree, differences of organisation proper, that is,\nof the arrangement of parts, in the widest sense of the word.[155]\n\n[154] We have not spoken about the hypothetic inheritance of pure\nphysiological adaptations, for it is clear without further discussion\nthat innate specific immunity, for instance, being a specific\n\u201cadaptedness\u201d (*see* p. 186) *might* be due to the inheritance of the\nresults of active immunity as an adaptation, just as adaptive congenital\nstructures *might* be due to such an inheritance.\n\n[155] C. E. v. Baer clearly discriminated between the type, the degree\nof organisation, and the histological structure. All these three topics\nindeed have to be taken into account separately; the third alone is of\nthe adaptive type. All of them may be independent of each other: the\nAmoeba may be as adapted histologically as is a high vertebrate, but it\nis of much lower type; and in its own type it is of a lower degree of\norganisation than Radiolaria are.\n\nWould it be possible to interpret the origin of this sort of systematic\ndiversities by a reasoning similar to that by which we have understood,\nat least hypothetically, congenital adaptedness?\n\nDogmatic Lamarckism, we know, uses two principles as its foundations;\none of them, adaptation and its inheritance, we have studied with what\nmay be called a partly positive result. The other is the supposed\nfaculty of the organism to keep, to store, and to transfer those\nvariations or mutations of a not properly adaptive sort which, though\noriginating by chance, happen to satisfy some needs of the organism.\n\n\nCRITICISM OF THE HYPOTHESIS OF STORING AND HANDING DOWN CONTINGENT\nVARIATIONS\n\nStrange to say, this second hypothesis of dogmatic Lamarckism, invented\nwith the express purpose of defeating Darwinism and taking the place of\nits fluctuating variability, which was found not to do justice to the\nfacts--this second hypothesis of dogmatic Lamarckism is liable to just\nthe same objections as dogmatic Darwinism itself.\n\nAs it is important to understand well the real logical nature of\nour objections to both of the great transformistic theories, we\nthink it well to interrupt our argument for a moment, in order to\nconsider a certain point which, though very important in itself,\nseems of only secondary importance to us in our present discussion.\nDogmatic Darwinism--I do not say the doctrine of Charles Darwin--is\nmaterialistic at bottom, and indeed has been used by many to complete\ntheir materialistic view of the universe on its organic side. The word\n\u201cmaterialism\u201d must not necessarily be taken here in its metaphysical\nsense, though most materialists are dogmatic metaphysicians. It also\ncan be understood as forming part of a phenomenological point of view.\nMaterialism as a doctrine of science means simply this: that whether\n\u201cnature\u201d be reality or phenomenon, in any case there is but one ultimate\nprinciple at its base, a principle relating to the movements of\nparticles of matter. It is this point of view which dogmatic Darwinism\nstrengthens; on the theory of natural selection and fluctuating\nvariations, due to accidental differences of nutrition, organisms are\nmerely arrangements of particles of matter, nothing else; and moreover,\ntheir kinds of arrangement are understood, at least in principle.\nLamarckism, on the other hand, is not materialistic, but most markedly\nvitalistic--psychistic even; it takes life for granted when it begins\nits explanations.\n\nYou may tell me that Darwin did the same, that he expressly states that\nhis theory has nothing to do with the origin of life; that the title\nof his work is \u201cThe Origin of *Species*.\u201d It would certainly be right\nto say so, at least with reference to Darwin personally; but in spite\nof that, it must be granted that Darwin\u2019s doctrine contains a certain\ngerm of materialism which has been fully developed by the Darwinian\ndogmatists, while Lamarckism is antimaterialistic by its very nature.\n\nNow it is very important, I think, to notice that this difference\nbetween the two theories is unable to disguise one main point which is\ncommon to both: and it is to this point, and to this point only, that\nour chief objections against both these theories converge at present.\n\nThe *contingency* of the typical organic form is maintained by Darwinism\nas well as by Lamarckism: both theories, therefore, break down for\nalmost the same reasons. The term \u201ccontingency\u201d can signify very\ndifferent relations, having but little in common; but it is sufficient\nfor our present purpose to observe that there may be distinguished\nroughly two main classes of contingencies, which may provisionally be\ncalled the \u201ccontingency of being,\u201d and the \u201ccontingency of occurring.\u201d\nIt is with the contingency of being that criticism of Darwinism and\nLamarckism of the dogmatic type has to deal. Darwinism dealt with\nvariations occurring at random; the organic form was the result of\na fixation of only one kind of such variations, all others being\nextinguished by selection. In other terms, the specific organised\nform, as understood by Darwinism, was a unit only to the extent that\nall its properties related to one and the same body, but for the rest\nit was a mere aggregation or summation. It may be objected to this\nstatement, that by being inherited in its specificity the Darwinian\nform proved to be a unit in a higher sense of the word, even in the\nopinion of dogmatic Darwinians; and this objection, perhaps, holds good\nas far as inheritance is concerned. But on the other hand, it must\nnever be forgotten that the word \u201cunit\u201d had quite a vague and empty\nmeaning even then, as indeed everything the organism is made up of\nis regarded as being in itself due to a contingent primary process,\nwhich has no relation to its fellow-processes. \u201cUnit,\u201d indeed, in spite\nof inheritance--which, by the way, is alleged also to be a merely\nmaterialistic event--means to Darwinians no more when applied to the\norganism than it does when applied to mountains or islands, where of\ncourse a sort of \u201cunit\u201d also exists in some sense, as far as one and the\nsame body comes into account, but where every single character of this\nunit, in every single feature of form or of quality, is the result of\nfactors or agents each of which is independent of every other.\n\nTo this sort of contingency of being, as maintained by Darwinians,\ncriticism has objected, as we know, that it is quite an impossible\nbasis of a theory of descent, since it would explain neither the first\norigin of an organ, nor any sort of harmony among parts or among whole\nindividuals, nor any sort of restitution processes.\n\nNow Lamarckism of the dogmatic kind, as will easily be seen, only\ndiffers from Darwinism in this respect, that what according to the\nlatter happens to the organism passively by means of selection, is\naccording to the former performed actively by the organism, by means of\na \u201cjudgment\u201d--by the retention and handing down of chance variations.\nThe specificity of the form as a whole is contingent also according\nto Lamarckism. And, indeed, criticism must reject this contingency of\nbeing in exactly the same way as it rejected the contingency of form\nmaintained by Darwinians.\n\nAs far as the inheritance of truly adaptive characters comes into\naccount--that is, the inheritance of characters which are due to the\nactive faculty of adaptation possessed by the organism, bearing a\nvitalistic aspect throughout--hardly anything could be said against\nLamarckism, except that inheritance of acquired characters is still\nan hypothesis of small and doubtful value at present. But that\n*specific organisation proper* is due to *contingent* variations, which\naccidentally have been found to satisfy some needs of the individual and\ntherefore have been maintained and handed down, this reasoning is quite\nan impossibility of exactly the same kind as the argument of Darwinism.\n\nThe process of restitution, perfect the very first time it occurs, if it\noccurs at all, is again the classical instance against this new sort of\ncontingency, which is assumed to be the basis of transformism. Here we\nsee with our eyes that the organism can do more than simply perpetuate\nvariations that have occurred at random and bear in themselves no\nrelation whatever to any sort of unit or totality. There *exists* a\nfaculty of a certain higher degree in the organism, and this faculty\ncannot possibly have originated by the process which Lamarckians[156]\nassume. But if their principle fails in one instance, it fails as a\n*general* theory altogether. And now, on the other hand, as we actually\nsee the individual organism endowed with a morphogenetic power,\ninexplicable by Lamarckism, but far exceeding the organogenetic faculty\nassumed by that theory, would it not be most reasonable to conclude from\nsuch facts, that there exists a certain organising power at the root of\nthe transformism of species also, a power which we do not understand,\nwhich we see only partially manifested in the work of restitutions,\nbut which certainly is not even touched by any of the Lamarckian\narguments? There does indeed exist what Gustav Wolff has called primary\npurposefulness (\u201cprim\u00e4re Zweckm\u00e4ssigkeit\u201d), at least in restitutions,\nand this is equally unexplainable by Darwinism and by the dogmatism of\nthe Lamarckians.\n\n[156] I repeat once more that we are dealing here with dogmatic\n\u201cNeo-\u201dLamarckism exclusively. This theory indeed claims to explain *all*\nfeatures and properties of organic bodies on the basis of the feeling\nof needs and storing of contingent fulfilments and on this basis alone,\njust as dogmatic \u201cNeo\u201d-Darwinism claims to account for *all* those\nphenomena on the ground of contingent variations and natural selection.\nDarwin himself, as we have seen, intentionally left unexplained certain\nprimary features of life and therefore cannot be blamed for having\nfailed to explain them, though even then his theory remains wrong.\nLamarck personally considered a real primary organisatory law of\nphylogeny as being of fundamental importance, and therefore he is not in\nthe least responsible if \u201cNeo-Lamarckism\u201d fails as a universal theory.\n\nBut before entering into this area of hypothesis, let us mention a few\nmore objections to be made to the theory of the contingency of form as\nput forward by Lamarckians. In the first place, let us say a few words\nabout the appropriateness of the term \u201ccontingency\u201d as used in this\nconnection. The forms are regarded as contingent by Lamarckians inasmuch\nas the variations which afterwards serve as \u201cmeans\u201d to the \u201cneeds\u201d of\nthe organism occur quite accidentally with regard to the whole organism.\nIt might be said that these \u201cneeds\u201d are not contingent but subject\nto an inherent destiny, but this plea is excluded by the Lamarckians\nthemselves, when they say that the organism experiences no need until it\nhas enjoyed the accidental fulfilment of the same. So the only thing in\nLamarckian transformism which is not of a contingent character would be\nthe psychological agent concerned in it, as being an agent endowed with\nthe primary power of feeling needs after it has felt fulfilment, and of\njudging about what the means of future fulfilment are, in order to keep\nthem whenever they offer. But these are characteristics of life itself,\nirrespective of all its specific forms, which alone are concerned in\ntransformism. Now indeed, I think, we see as clearly as possible that\nDarwinism and Lamarckism, in spite of the great contrast of materialism\nand psychologism, shake hands on the common ground of the contingency of\norganic forms.\n\nThe whole anti-Darwinistic criticism therefore of Gustav Wolff for\ninstance, may also be applied to Lamarckism with only a few changes\nof words. How could the origin of so complete an organ as the eye of\nvertebrates be due to contingent variations? How could that account for\nthe harmony of the different kinds of cells in this very complicated\norgan with each other and with parts of the brain? And how is it to be\nunderstood, on the assumption of contingency, that there are two eyes of\nalmost equal perfection, and that there are two feet, two ears? Islands\nand mountains do not show such symmetry in *their* structures.\n\nWe shall not repeat our deduction of the origin of restitutions, of\nregeneration for instance, on the dogmatic Lamarckian theory. As we\nhave said already, it would lead to absurdities as great as in the\ncase of dogmatic Darwinism, and indeed we already have mentioned that\nLamarckians would hardly even attempt to explain these phenomena.\nIt follows that dogmatic Lamarckism fails as a general theory about\nform.[157]\n\n[157] Compare also the excellent criticism of Lamarckism lately given by\nG. Wolff, *Die Begr\u00fcndung der Abstammungslehre*, M\u00fcnchen, 1907.\n\nThere is finally one group of facts often brought forward against\nLamarckism by Darwinian authors[158] which may be called the logical\n*experimentum crucis* of this doctrine, an *experimentum* destined\nto prove fatal. You know that among the polymorphic groups of bees,\ntermites, and ants, there exists one type of individuals, or even\nseveral types, endowed with some very typical features of organisation,\nbut at the same time absolutely excluded from reproduction: how could\nthose morphological types have originated on the plan allowed by the\nLamarckians? Of what use would \u201cjudgment\u201d about means that are offered\nby chance and happen to satisfy needs, be to individuals which die\nwithout offspring? Here Lamarckism becomes a simple absurdity, just as\nDarwinism resulted in absurdities elsewhere.\n\n[158] It has also very often been said by Darwinians that Lamarckism is\nonly able to explain those cases of adaptedness which relate to active\nfunctioning but not mere passive adapted characters, like \u201cmimicry\u201d for\nexample. But this argument *taken by itself*, it seems to me, would not\nbe fatal to Neo-Lamarckism in the special form August Pauly gave to this\ndoctrine.\n\nWe were speaking about dogmatic Darwinism then, and it is about dogmatic\nLamarckism that we are reasoning at present; both theories must fall in\ntheir dogmatic form, though a small part of both can be said to stand\ncriticism. But these two parts which survive criticism, one offered by\nLamarck, the other by Darwin, are far from being a complete theory of\ntransformism, even if taken together: they only cover a small area of\nthe field concerned in the theory of descent. Almost everything is still\nto be done, and we may here formulate, briefly at least, what we expect\nto be accomplished by the science of the future.\n\n\n4. THE REAL RESULTS AND THE UNSOLVED PROBLEMS OF TRANSFORMISM\n\nWhat has been explained to a certain extent by the two great theories\nnow current is only this. Systematic diversities consisting in mere\ndifferences as to intensity or number may perhaps owe their origin to\nordinary variation. They may at least, if we are entitled to assume\nthat heredity in some cases is able to hand on such variations without\nreversion, which, it must be again remarked, is by no means proved by\nthe facts at present. Natural selection may share in this process by\neliminating all those individuals that do not show the character which\nhappens to be useful. That is the Darwinian part of an explanation of\ntransformism which may be conceded as an hypothesis. On the other side,\ncongenital histological adaptedness may be regarded hypothetically as\ndue to an inheritance of adaptive characters which had been acquired by\nthe organism\u2019s activity, exerted during a great number of generations.\nThat is the Lamarckian part in the theory of descent.\n\nBut nothing more is contributed to this theory either by the doctrine\nof Darwin or by that of Lamarck. So it follows that almost everything\nhas still to be done; for no hypothesis at present accounts for\nthe foundation of all systematics, viz., for the differences in\norganisation, in all that relates to the so-called types as such and\nthe degree of complication in these types, both of which (types and\ndegree of complication) are independent of histological adaptation and\nadaptedness.\n\nWhat then do we know about any facts that might be said to bear on\nthis problem? We have stated already at the end of our chapter devoted\nto the analysis of heredity that what we actually know about any\ndeviation of inheritance proper, that is, about congenital differences\nbetween the parents and the offspring, relating to mere tectonics,\nis practically nothing: indeed, there are at our disposal only the\nfew facts observed by de Vries or derived from the experience of\nhorticulturalists and breeders. We may admit that these facts at\nleast prove the possibility[159] of a discontinuous variation, that\nis of \u201cmutation,\u201d following certain lines of tectonics and leading to\n*constant* results; but everything else, that is everything about a real\ntheory of phylogeny, must be left to the taste of each author who writes\non the theory of the Living. You may call that a very unscientific state\nof affairs, but no other is possible.\n\n[159] But nothing more. All \u201cmutations\u201d hitherto observed in nature\nor (comp. page 238, note 3) experimentally produced relate only to\n\u201cvarieties\u201d and not to \u201cspecies.\u201d One could hardly say that the\nrecent investigations about the production of mutations by *external*\nmeans have strengthened their importance for the general theory of\ntransformism.\n\nAnd, in fact, it has been admitted by almost all who have dealt with\ntransformism without prepossessions that such is the state of affairs.\nLamarck himself, as we have mentioned already, was not blind to the fact\nthat a sort of organisatory law must be at the base of all transformism,\nand it is well known that hypothetical statements about an original law\nof phylogeny have been attempted by N\u00e4geli, K\u00f6lliker, Wigand, Eimer,\nand many others. But a full discussion of all these \u201claws\u201d would hardly\nhelp us much in our theoretical endeavour, as all of them, it must be\nconfessed, do little more than state the mere fact that some unknown\nprinciple of organisation must have been at work in phylogeny, if we are\nto accept the theory of descent at all.\n\nIt is important to notice that even such a convinced Darwinian as\nWallace, who is well known to have been an independent discoverer of the\nelimination principle, admitted an exception to this principle in at\nleast one case--with regard to the origin of man. But one exception of\ncourse destroys the generality of a principle.\n\nAs we ourselves feel absolutely incapable of adding anything specific\nto the general statement that there *must* be an unknown principle of\ntransformism, if the hypothesis of descent is justified at all, we may\nhere close our discussion of the subject.\n\n\n5. THE LOGICAL VALUE OF THE ORGANIC FORM ACCORDING TO THE DIFFERENT\nTRANSFORMISTIC THEORIES\n\nA few words only must be added about two topics: on the character of\norganic forms as regarded by the different transformistic theories, and\non the relation of transformism in general to our concept of entelechy.\n\nWe have learnt that both Darwinism and Lamarckism, in their dogmatic\nshape, regard the specific forms of animals and plants as being\ncontingent; in fact, it was to this contingency that criticism was\nmainly directed. We therefore are entitled to say that to Darwinism and\nLamarckism organic forms are accidental in the very sense of the *forma\naccidentalis* of the old logicians. There are indefinite forms possible,\naccording to these theories, and there is no law relating to these\nforms. Systematics, under such a view, must lose, of course, any really\nfundamental importance. \u201cThere is no rational system about organisms\u201d:\nthat is the ultimate statement of Darwinism and of Lamarckism on this\ndoubtful question. Systematics is a mere catalogue, not at present\nonly, but for ever, by the very nature of the organisms. It is not\nowing to the indefinite number of possible forms that both our theories\ncame to deny the importance of systematics, but to the want of a *law*\nrelating to this indefinite number: among chemical compounds indefinite\npossibilities also exist in some cases, but they obey the law of the\ngeneral formula. It is very strange that Darwinians of all people are\nin the forefront of systematic research in all countries: do they not\nsee that what they are trying to build up can only relate to accidental\nphenomena? Or have they some doubts about the foundations of their own\ntheoretical views, in spite of the dogmatic air with which they defend\nthem? Or is it the so-called historical interest which attracts them?\n\nA new question seems to arise at this point: Have not we ourselves\nneglected history in favour of systematics and laws? Our next lecture,\nthe last of this year, will give the answer to this question.\n\nAt present we continue our study of the possible aspects of systematics.\nIt is not difficult to find out what meaning organic forms would assume\nunder any phylogenetic theory opposed to the theories of contingency.\nIt was their defence of contingency, that is, their lack of any law\nof forms, that caused these theories to be overthrown--reduced to\nabsurdities even--and therefore, it follows that to assume any kind of\ntransformistic law is at the same time to deny the accidental character\nof the forms of living beings.\n\nThere is no *forma accidentalis*. Does that mean that the *forma\nessentialis* is introduced by this mere statement? And what would *that*\nassert about the character of systematics?\n\n\nTHE ORGANIC FORM AND ENTELECHY\n\nThis problem is not as simple as it might seem to be at the first\nglance, and, in fact, it is insoluble at present. It is here that the\nrelation of the hypothetic transformistic principle to our concept of\nentelechy is concerned.\n\nWe know that entelechy, though not material in itself, uses material\nmeans in each individual morphogenesis, handed down by the material\ncontinuity in inheritance. What then undergoes change in phylogeny,\nthe means or the entelechy? And what would be the logical aspect of\nsystematics in either case?\n\nOf course there would be a law in systematics in any case; and therefore\nsystematics in any case would be rational in principle. But if the\ntransformistic factor were connected with the means of morphogenesis,\none could hardly say that specific form as such was a primary essence.\nEntelechy would be that essence, but entelechy in its generality and\nalways remaining the same in its most intimate character, as the\nspecific diversities would only be due to a something, which is not\nform, but simply means to form. But the *harmony* revealed to us in\nevery typical morphogenesis, be it normal or be it regulatory, seems\nto forbid us to connect transformism with the means of morphogenesis.\nAnd therefore we shall close this discussion about the most problematic\nphenomena of biology with the declaration, that we regard it as more\ncongruent to the general aspect of life to correlate the unknown\nprinciple concerned in descent with entelechy itself, and not with\nits means. Systematics of organisms therefore would be in fact\nsystematics of entelechies, and therefore organic forms would be\n*formae essentiales*, entelechy being the very essence of form in its\nspecificity. Of course systematics would then be able to assume a truly\nrational character at some future date: there might one day be found\na principle to account for the totality of possible[160] forms, a\nprinciple based upon the analysis of entelechy.[161] As we have allowed\nthat Lamarckism hypothetically explains congenital adaptedness in\nhistology, and that Darwinism explains a few differences in quantity,\nand as such properties, of course, would both be of a contingent\ncharacter, it follows that our future rational system would be combined\nwith certain accidental diversities. And so it might be said to be\none of the principal tasks of systematic biological science in the\nfuture to discover the really rational system among a given totality of\ndiversities which cannot appear rational at the first glance, one sort\nof differences, so to speak, being superimposed upon the other.\n\n[160] The word \u201cpossible\u201d relating to originating, of course, not to\nsurviving. It is here that natural selection may acquire its logical\nimportance alluded to above (see page 264).\n\n[161] The discussions in the second volume of this book will show the\npossible significance of such an analysis. We at present are dealing\nwith entelechy in a quasi-popular manner.\n\n\n\n\n*C.* THE LOGIC OF HISTORY\n\n\nHistory, in the strictest sense of the word, is the enumeration of the\nthings which have followed one another in order of time. History deals\nwith the single, with regard both to time and space. Even if its facts\nare complex in themselves and proper to certain other kinds of human\nstudy, they are nevertheless regarded by history as single. Facts, we\nhad better say, so far as they are regarded as single, are regarded\nhistorically, for what relates to specific time and space is called\nhistory.\n\nTaken as a simple enumeration or registration, history, of course,\ncannot claim to be a \u201cscience\u201d unless we are prepared to denude that\nword of all specific meaning. But that would hardly be useful. As a\nmatter of fact, what has actually claimed to be history, has always\nbeen more than a mere enumeration, even in biology proper. So-called\nphylogeny implies, as we have shown, that every one of its actual\nforms contains some rational elements. Phylogeny always rests on\nthe assumption that only some of the characters of the organisms\nwere changed in transformism and that what remained unchanged may be\nexplained by the fact of inheritance.\n\nBut this, remember, was the utmost we were able to say for phylogeny.\nIt remains fantastic and for the most part unscientific in spite of\nthis small degree of rationality, as to which it is generally not very\nclear itself. For nothing is known with regard to the positive factors\nof transformism, and we were only able to offer the discussion of a few\npossibilities in place of a real theory of the factors of descent.\n\nIn spite of that it will not be without a certain logical value to begin\nour analysis of history in general by the discussion of possibilities\nagain. Biology proper would hardly allow us to do more: for the\nsimple \u201cfact\u201d of history is not even a \u201cfact\u201d in this science, but an\nhypothesis, albeit one of some probability.\n\nAs discussions of mere possibilities should always rest on as broad a\nbasis as possible, we shall begin our analysis by raising two general\nquestions. To what kinds of realities may the concept of history\nreasonably be applied? And what different types of \u201chistory\u201d would be\npossible *a priori*, if the word history is to signify more than a mere\nenumeration?\n\n\n1. THE POSSIBLE ASPECTS OF HISTORY\n\nOf course, we could select one definite volume in space and call all the\nconsecutive stages which it goes through, its history: it then would be\npart of its history that a cloud was formed in it, or that a bird passed\nthrough it on the wing. But it would hardly be found very suggestive to\nwrite the history of space-volumes. In fact, it is to *bodies* in space\nthat all history actually relates, at least indirectly, for even the\nhistory of sciences is in some respect the history of men or of books.\nIt may suffice for our analysis to understand here the word body in its\npopular sense.\n\nNow in its relation to bodies history may have the three following\naspects, as far as anything more than a simple enumeration comes into\naccount. Firstly, it may relate to one and the same body, the term\nbody again to be understood popularly. So it is when the individual\nhistory of the organism is traced from the egg to the adult, or when the\nhistory of a cloud or of an island or of a volcano is written. Secondly,\nthe subject-matter of history may be formed by the single units of a\nconsecutive series of bodies following each other periodically. To this\nvariety of history the discoveries of Mendel and his followers would\nbelong in the strictest sense, but so does our hypothetical phylogeny\nand a great part of the history of mankind. And lastly, there is a\nrather complicated kind of sequence of which the \u201chistory\u201d has actually\nbeen written. History can refer to bodies which are in no direct\nrelation with one another, but which are each the effect of another body\nthat belongs to a consecutive series of body-units showing periodicity.\nThis sounds rather complicated; but it is only the strict expression\nof what is perfectly familiar to you all. Our sentence indeed is\nsimply part of the definition of a history of art or of literature for\ninstance--or, say, of a phylogenetic history of the nests of birds. The\nsingle pictures are the subjects of the history of art, and nobody would\ndeny that these pictures are the effects of their painters, and that\nthe painters are individuals of mankind--that is, that they are bodies\nbelonging to a consecutive series of body-units showing periodicity. Of\ncourse, it is only improperly that we speak of a history of pictures or\nof books or of nests. In fact, we are dealing with painters, and with\nmen of letters or of science, and with certain birds, and therefore\nthe third type of history may be reduced to the second. But it was not\nwithout value to pursue our logical discrimination as far as possible.\n\nSo far we have always spoken of history as being more than a mere\nenumeration, but we have not ascertained what this \u201cmore\u201d signifies. It\nis not very difficult to do so: in fact, there are three different types\nof history, each of a different degree of importance with respect to the\nunderstanding of reality.\n\nIn the first place, history may start as a mere enumeration at the\nbeginning, and at the end, in spite of all further endeavour, may\n*remain* that and nothing more. That may occur in the first as well\nas in the second group of our division of history with regard to\nits relation to bodies. Take a cloud and describe its history from\nthe beginning to the end: there would never be much more than pure\ndescription. Or take one pair of dogs and describe them and their\noffspring for four generations or more: I doubt if you will get beyond\nmere descriptions in this case either. The only step beyond a mere\nenumeration which we can be said to have advanced in these instances,\nconsists in the conviction, gained at the end of the analysis, that\nnothing more than such an enumeration is in any way *possible*.\n\nQuite the opposite happens when \u201chistory\u201d deals with the individual\nfrom the egg to the adult: here the whole series of historical facts is\nseen to form one whole. This case therefore we shall call not history,\nbut *evolution*, an evolving of something; the word \u201cevolution\u201d being\nunderstood here in a much wider sense than on former occasions,[162] and\n*including*, for instance, the embryological alternative \u201cevolutio\u201d or\n\u201cepigenesis.\u201d\n\n[162] See pp. 26, 45, 54, etc.\n\nAnd half-way between enumeration and evolution there now stands a type\nof history which is more than the one and less than the other: there is\na kind of intelligible connection between the consecutive historical\nstages and yet the concept of a whole does not come in. The geological\nhistory of a mountain or of an island is a very clear instance of this\nclass. It is easy to see here, how what *has been* always becomes the\nfoundation of what *will be* in the *next* phase of the historical\nprocess. There is a sort of *cumulation* of consecutive phases, the\nlater ones being impossible without the earlier. So we shall speak\nof the type of \u201chistorical cumulation\u201d as standing between evolution\nand bare temporal sequence. By means of historical cumulations history\nmay fairly claim to \u201cexplain\u201d things. We \u201cunderstand\u201d a mountain or an\nisland in all its actual characteristics, if we know its history. This\n\u201chistorical understanding\u201d rests on the fact that what first appeared\nas an inconceivable complex has been resolved into a sequence of single\nevents, each of which may claim to have been explained by actually\nexisting sciences. The complex has been explained as being, though not\na real \u201cwhole,\u201d yet a sum of singularities, every element of which is\nfamiliar.\n\nBut you may tell me that my discussion of evolution and of cumulation,\nas the higher aspects of history, is by no means complete; nay,\nmore--that it is altogether wrong. You would certainly not be mistaken\nin calling my analysis incomplete. We have called one type of history\nevolution, the other cumulation; but how have these higher types been\nreached? Has historical enumeration itself, which was supposed to\nstand at the beginning of all analysis, or has \u201chistory\u201d itself in its\nstrictest sense, as relating to the single as such, risen unaided into\nsomething more than \u201chistory\u201d? By no means: history has grown beyond\nits bounds by the aid of something from without. It is unhistorical\nelements that have brought us from mere history to more than history.\nWe have created the concept of evolution, not from our knowledge of the\nsingle line of events attendant on a single egg of a frog, but from our\nknowledge that there are billions or more of frogs\u2019 eggs, all destined\nto the same \u201chistory,\u201d which therefore is not history at all. We have\ncreated the concept of cumulation not from the historical study of\na single mountain, but from our knowledge of physics and chemistry\nand so-called dynamical geology: by the aid of these sciences we\n\u201cunderstood\u201d historically, and thus our understanding came from another\nsource than history itself.\n\n\n2. PHYLOGENETIC POSSIBILITIES\n\nDoes history always gain its importance from what it is not? Must\nhistory always lose its \u201chistorical\u201d aspect, in order to become of\nimportance to human knowledge? And can it *always* become \u201cscience\u201d by\nsuch a transformation? We afterwards shall resume this discussion on\na larger scale, but at present we shall apply what we have learned to\nhypothetic phylogeny. What then are the possibilities of phylogeny, to\nwhat class of history would it belong if it were complete? Of course, we\nshall not be able to answer this question fully; for phylogeny is *not*\ncomplete, and scarcely anything is known about the factors which act\nin it. But in spite of that, so much, it seems to me, is gained by our\nanalysis of the possible aspects of history and of the factors possibly\nconcerned in transformism, that we are at least able to formulate the\npossibilities of a phylogeny of the future in their strict logical\noutlines.\n\nDarwinism and Lamarckism, regarding organic forms as contingent, must\nat the same time regard organic history as a cumulation; they indeed\n*might* claim to furnish an historical explanation in the realm of\nbiology--if only their statements were unimpeachable, which as we have\nseen, they are not.\n\nBut any transformistic theory, which locates the very principle of\nphylogeny in the organism itself, and to which therefore even organic\nforms would be not accidental but essential, might be forced to regard\nthe descent of organisms as a true evolution. The singularities in\nphylogenetic history would thus become links in one whole: history\nproper would become more than history. But I only say that phylogeny\n*might* be evolution, and in fact I cannot admit more than this *a\npriori*, even on the basis of an internal transformistic principle,\nas has been assumed. Such a principle also might lead always from one\ntypical state of organisation to the next: but *ad infinitum*.[163]\nThen phylogeny, though containing what might in some sense be called\n\u201cprogress,\u201d would not be \u201cevolution\u201d; it might even be called cumulation\nin such a case, in spite of the internal transforming principle, though,\nof course, cumulation from within would always mean something very\ndifferent from cumulation from without.[164]\n\n[163] An immanent vitalistic phylogeny *without* a pre-established end\nhas recently been advocated by H. Bergson (*L\u2019\u00e9volution cr\u00e9atrice*,\nParis, 1907).\n\n[164] In this connection the problem may be raised, whether there can be\nsuch a thing as unchangeable \u201cspecies\u201d in spite of the mutability of the\nindividuals. Compare page 251, note 1.\n\nBut we must leave this problem an open question, as long as our actual\nknowledge about transformism remains as poor as it is. We need only add,\nfor the sake of logical interest, that phylogeny, as a true evolution,\nwould necessarily be characterised by the possibility of being repeated.\n\n\n3. THE HISTORY OF MANKIND\n\nWe only assume hypothetically that phylogeny has happened, and we know\nscarcely anything about the factors concerned in it. Now, it certainly\nwould be of great importance, if at least in a small and definite field\nof biology we were able to state a little more, if the *mere fact* of\nphylogeny, of \u201chistory,\u201d were at least beyond any doubt within a certain\nrange of our biological experience. And indeed there is one department\nof knowledge, where history, as we know, *has happened*, and where we\nalso know at least some of the factors concerned in it.\n\nI refer to the history of mankind; and I use the expression not at all\nin its anthropological or ethnographical sense, as you might expect\nfrom a biologist, but in its proper and common sense as the history of\npolitics and of laws and of arts, of literature and of sciences: in a\nword, the history of civilisation. Here is the only field, where we know\nthat there actually *are* historical facts: let us try to find out what\nthese facts can teach us about their succession.\n\nThe theory of history in this narrower meaning of the word has been\nthe subject of very numerous controversies in the last twenty years,\nespecially in Germany, and these controversies have led very deeply into\nthe whole philosophical view of the universe. We shall try to treat our\nsubject as impartially as possible.\n\nHegel says, in the introduction to his *Ph\u00e4nomenologie des Geistes*:\n\u201c*Die Philosophie muss sich h\u00fcten erbaulich sein zu wollen*\u201d\n(\u201cPhilosophy must beware of trying to be edifying\u201d). These words,\nindeed, ought to be inscribed on the lintel of the door that leads\ninto historical methodology, for they have been sadly neglected by\ncertain theoretical writers. Instead of analysing history in order to\nsee what it would yield to philosophy, they have often made philosophy,\nespecially moral philosophy, the starting-point of research, and history\nthen has had to obey certain doctrines from the very beginning.\n\nWe shall try as far as we can not to become \u201cerbaulich\u201d in our\ndiscussions. We want to learn from history for the purposes of\nphilosophy, and we want to learn from history as from a phenomenon in\ntime and in space, just as we have learnt from all the other phenomena\nregarding life in nature. Every class of phenomena of course may\nbe studied with respect to generalities as well as with respect to\nparticulars. The particular, it is true, has not taught us much in our\nstudies so far. Perhaps it may be successful in the domain of history\nproper.\n\nIf I take into consideration what the best authors of the last century\nhave written about human history with respect to its general value, I\ncannot help feeling that none of them has succeeded in assigning to\nhistory a position where it would really prove to be of great importance\nfor the aims of philosophical inquiry. Is that the fault of the authors\nor of human history? And what then would explain the general interest\nwhich almost every one takes, and which I myself take in history in\nspite of this unsatisfactory state of things?\n\n\nCUMULATIONS IN HUMAN HISTORY\n\nLet us begin our analytical studies of the value and the meaning of\nhuman history, by considering some opinions which deserve the foremost\nplace in our discussion, not as being the first in time, but as being\nthe first in simplicity. I refer to the views of men like Buckle, Taine,\nand Lamprecht, and especially Lamprecht, for he has tried the hardest to\njustify theoretically what he regards the only scientific aim of history\nto be. If we may make use of our logical scheme of the three possible\naspects of history, it is clear from the beginning that the history of\nmankind, as understood by the three authors we have named, but most\nparticularly by Lamprecht, is neither a mere enumeration nor a true\nevolution, but that it has to do with *cumulations*, in the clearest\nof their possible forms. The processes of civilisation among the\ndifferent peoples are in fact to be compared logically with the origin\nof volcanoes or mountain-ranges in Japan, or in Italy, or in America,\nand show us a typical series of consecutive phases, as do these. There\nexists, for instance, in the sphere of any single civilisation an\neconomic system, founded first on the exchange of natural products,\nand then on money. There are, or better, perhaps, there are said to\nbe, characteristic phases succeeding one another in the arts, such as\nthe \u201ctypical,\u201d the \u201cindividualistic,\u201d and the \u201csubjective\u201d phases. Any\ncivilisation may be said to have its \u201cmiddle ages,\u201d and so on. All these\nare \u201claws\u201d of course in the meaning of \u201crules\u201d only, for they are far\nfrom being elemental, they are not \u201cprinciples\u201d in any sense. And there\nare other sorts of \u201crules\u201d at work for exceptional cases: revolutions\nhave their rules, and imperialism, for instance, has its rules also.\n\nNow, as the consecutive phases of history have been shown to be\ntrue cumulations, it follows that the rules which are revealed by\nour analysis, are rules relating to the very origin of cumulations\nalso. The real *element* upon which the cumulation-phases, and the\ncumulation-rules together rest, is the human individual as the bearer\nof its psychology. Nobody, it seems to me, has shown more clearly than\nSimmel that it is the human individual, *qua* individual, which is\nconcerned in *every* kind of history.\n\nHistory, viewed as a series of cumulations, may in fact claim to\nsatisfy the intellect by \u201cexplaining\u201d a good deal of historical facts.\nIt explains by means of the elemental factor of individual psychology,\nwhich every one knows from himself, and by the simple concept that there\nis a cumulation, supported by language and by writing as its principal\nfactors, which both of course rest on psychology again. Psychology,\nso we may say, is capable of leading to cumulation phenomena; the\ncumulations in history are such that we are able to understand them by\nour everyday psychology; and history, so far as it is of scientific\nvalue, consists exclusively of cumulations.\n\nNo doubt there is much truth in such a conception of history; but\nno doubt also, it puts history in the second rank as compared with\npsychology; just as geology stands in the second rank as compared with\nchemistry or physics. Geology and human history may lead to generalities\nin the form of rules, but these rules are *known* to be not elemental\nbut only cumulative; and moreover, we know the elements concerned in\nthem. The elements, therefore, are the real subjects for further studies\nin the realm of philosophy, but not the cumulations, not the rules,\nwhich are known to be due to accidental constellations. Of course, the\n\u201csingle\u201d is the immediate subject of this sort of history, but the\nsingle as such is emphatically pronounced to be insignificant, and the\ncumulations and the cumulative rules, though \u201csingles\u201d in a higher sense\nof the word, are shown to be anything but elementalities.\n\nTherefore, on a conception of human history such as that of Buckle,\nTaine, Lamprecht, and others, we, of course, ought to take an interest\nin history, because what is \u201cexplained\u201d by historical research touches\nall of us most personally every day and every year. But our philosophy,\nour view of the world, would remain the same without history as it is\nwith it. We only study history, and especially the history of our own\ncivilisation, because it is a field of actuality which directly relates\nto ourselves, just as we study for practical purposes the railway\ntime-tables of our own country, but not of Australia; just as we study\nthe local time-table in particular.\n\nIf the mere *rerum cognoscere causas* is regarded as the criterium of\nscience, history of Lamprecht\u2019s type of course is a science, for its\nexplanations rest upon the demonstration of the typical constellations\nand of the elemental factor or law from which together the next\nconstellations are known necessarily to follow. But history of this kind\nis not a science in the sense of discovering *den ruhenden Pol in der\nErscheinungen Flucht*.\n\n\nHUMAN HISTORY NOT AN \u201cEVOLUTION\u201d\n\nQuite another view of history has been maintained by Hegel, if his\nexplanations about the *Entwicklung des objectiven Geistes* (\u201cthe\ndevelopment of the objective mind\u201d) may be co-ordinated with our\nstrictly logical categories of the possible aspects of history. But I\nbelieve we are entitled to say that it was a real *evolution* of mankind\nthat Hegel was thinking of; an evolution regarding mankind as spiritual\nbeings and having an end, at least ideally. One psychical state was\nconsidered by Hegel to generate the next, not as a mere cumulation\nof elemental stages, but in such a way that each of the states would\nrepresent an elementality and an irreducibility in itself; and he\nassumed that there was a continuous series of such stages of the mind\nthrough the course of generations. Is there any sufficient reason in\nhistorical facts for such an assumption?\n\nThe mind \u201cevolves\u201d itself from error to truth by what might be called\na system of contradictions, according to Hegel, with respect to logic\nas well as to morality; the sum of such contradictions becoming smaller\nand less complicated with every single step of this evolution. No doubt\nthere really occurs a process of logical and moral refining, so to say,\nin the individual, and no doubt also, the results of this process,\nas far as attained, can be handed down to the next generation by the\nspoken word or by books. But it is by no means clear, I think, that this\nprocess is of the type of a real evolution towards an end, so far as it\nrelates to the actual series of generations as such. On the contrary,\nit seems to me that we have here simply what we meet everywhere in\nhistory--a sort of cumulation resting upon a psychological basis.\n\nThe dissatisfaction that exists at any actual stage of contradiction,\nboth moral and logical, is one of the psychical factors concerned;\nthe faculty of reasoning is the other. Now it is a consequence of the\nreasoning faculty that the dissatisfaction continually decreases, or\nat least changes in such a way that each partial result of the logical\nprocess brings with it the statement of new problems. The number of\nsuch problems may become less, as the logical process advances, and,\nindeed, there is an ideal state, both logical and moral, in which there\nare no more problems, but only results, though this ideal could hardly\nbe regarded as attainable by the *human* mind. In the history of those\nsciences which are wholly or chiefly of the *a priori* type, this\nprocess of deliverance from contradictions is most advantageously to\nbe seen. It is obvious in mechanics and thermodynamics, and the theory\nof matter is another very good instance. A certain result is reached;\nmuch seems to be gained, but suddenly another group of facts presents\nitself, which had been previously unknown or neglected. The first result\nhas to be changed or enlarged; many problems of the second order arise;\nthere are contradictions among them, which disappear after a certain\nalteration of what was the first fundamental result, and so on. And the\nsame is true about morality, though the difficulties are much greater\nhere, as a clear and well-marked standard of measurement of what is good\nand what is bad, is wanting, or at least, is not conceded unanimously.\nBut even here there is a consensus on some matters: one would hardly go\nback to slavery again, for instance, and there are still other points\nin morality which are claimed as ideals at least by a great majority of\nmoral thinkers.\n\nBut all this is not true \u201cevolution,\u201d and indeed, I doubt if such an\nevolution of mankind could be proved at present in the sense in which\nHegel thought it possible. The process of logical and moral deliverance\nfrom contradictions *might* come to an end in *one* individual; at least\nthat is a logical possibility, or it might come to an end in, say,\nsix or ten generations. And there is, unfortunately for mankind, no\nguarantee that the result will not be lost again and have to be acquired\na second time. All this proves that what Hegel regarded as an evolution\nof the race is only a cumulation. There is nothing evolutionary relating\nto the generations of mankind as such. At least, nothing is proved about\nsuch an evolution.[165]\n\n[165] On account of the limited size of the earth a certain final stage\nof human civilisation might be expected in a future time; but it would\nbe the size of the earth which determined this end, and not the process\nof civilisation itself.\n\nYou may call my view pessimistic, and indeed you may be right so far\nas the sum total of human beings as such is in question. But, be it\npessimistic or not, we are here moving on scientific ground only, and\nhave merely to study the probability or improbability of problematic\nfacts, and with such a view in our mind, we are bound to say that a\ntrue logical and moral evolution of mankind is not at all supported\nby known facts. There is a process of logical and moral perfection,\nbut this process is *not one*, is not \u201csingle\u201d in its actuality; it is\nnot connected with the one and single line of history, but only with a\nfew generations each time it occurs, or even with one individual, at\nleast ideally. And this process is not less a process of cumulation\nthan any other sort of development or so-called \u201cprogress\u201d in history\nis. Philosophers of the Middle Ages, in fact, sometimes regarded human\nhistory as *one* evolutionary unity, beginning with the Creation and\nending with the Day of Judgment; but every one must agree, I think,\nthat even under the dogmatic assumptions of orthodoxy history would by\nno means *necessarily* be an \u201cevolution.\u201d Even then the paths taken by\ndifferent individuals or different branches of the human race on their\nway to redemption *can* be regarded as independent lines.\n\nThus Hegel\u2019s conception of an evolution of mankind, it seems to me,\nfails to stand criticism. By emphasising that there are certain lines of\ndevelopment in history which bring with them a stimulus to perfection,\nand that these lines relate to all that is highest in culture, Hegel\ncertainly rendered the most important service to the theory of history;\nbut in spite of that he has revealed to us only a special and typical\nkind of cumulation process, and nothing like an evolution. We may say\nthat the very essence of history lies in this sort of cumulation, in\nthis \u201cpseudo-evolution\u201d as we might say; and if we like to become moral\nmetaphysicians we might add, that it is for the sake of the possibility\nof this sort of cumulation that man lives his earthly life; the Hindoos\nsay so, indeed, and so do many Christians. But even if we were to depart\nfrom our scientific basis in this way we should not get beyond the realm\nof cumulations.\n\nAll this, of course, is not to be understood to affirm that there never\n*will* be discovered any real evolutionary element in human history--in\nthe so-called \u201csubconscious\u201d sphere perhaps--but at present we\ncertainly are ignorant of such an element.\n\n\nTHE PROBLEM OF THE \u201cSINGLE\u201d AS SUCH\n\nIf history has failed to appear as a true evolution, and if, on the\nother hand, it reveals to us a great sum of different cumulations, some\nof very great importance, others of minor importance, what then remains\nof the importance of the single historical event in its very singleness?\nWhat importance can the description of this event have with regard to\nour scientific aims? We could hardly say at present that it appears to\nbe of very much importance at all. The historical process as a whole\nhas proved to be not a real elemental unit, as far as we know, and such\nelemental units as there are in it have proved to be of importance only\n*for* individual psychology but not *as* history. History has offered\nus only instances of what every psychologist knew already from his own\nexperience, or at least might have known if he had conceived his task in\nthe widest possible spirit.\n\nBut is no other way left by which true history might show its real\nimportance in spite of all our former analysis? Can history be saved\nperhaps to philosophical science by any new sort of reasoning which we\nhave not yet applied to it here.\n\nAs a matter of fact, such new reasoning has been tried, and\nRickert,[166] in particular, has laid much stress upon the point\nthat natural sciences have to do with generalities, while historical\nsciences have to do with the single in its singleness only, and, in\nspite of that, are of the highest philosophical importance. He does not\nthink very highly of so-called \u201chistorical laws,\u201d which must be mere\nborrowings from psychology or biology, applied to history proper, and\nnot touching its character as \u201chistory.\u201d We agree with these statements\nto a considerable extent. But what then about \u201chistory proper,\u201d what\nabout \u201cthe single in its very singleness\u201d?\n\n[166] *Die Grenzen der naturwissenschaftlichen Begriffsbildung*,\nT\u00fcbingen and Leipzig, 1902.\n\nLet us say at first a few words about this term \u201csingle\u201d so very often\napplied by us. In the ultimate meaning of the word, of course, the\nseries of actual sensations or \u201cpresentations\u201d is the \u201csingle\u201d which is\ngiven \u201chistorically\u201d to each individual, and therefore to the writer of\nhistory also, and in fact, history as understood by Rickert is based\nto a great extent upon this primordial meaning of single \u201cgivenness.\u201d\nThe word \u201csingle,\u201d in his opinion, relates to the *actual and true\nspecification* of any event, or group of events, at a given time and\nat a given locality in space, these events possessing an identity of\ntheir own and never being repeated without change of identity. If the\nsubject-matter of history is defined like this, then there are, indeed,\n\u201cGrenzen der naturwissenschaftlichen Begriffsbildung\u201d with regard to\nhistory, for natural sciences have nothing to do with the single in such\nan understanding of the word.\n\nRickert says somewhere that history as a real evolution, as one\ntotality of a higher order, would cease to be proper history: and he\nis right. History, in fact, would soon lose the character of specific\nattachment to a given space and to a given time, and would lose its\n\u201cnon-repeatability,\u201d in the logical sense at least, if it were one\n*unit* in reality: as soon as it was that, it would have become a\nlogical generality, an element in nature, so to say, in spite of its\nfactual singularity. But history is not obliged to become that, Rickert\nstates; and we may add that history in fact cannot become that, because\nit simply proves not to be an evolution as far as we know at present.\n\nBut what importance does Rickert attach to his history specified and\nnon-repeatably single?\n\nHistory has a logic of its own, he says; the scheme of its logic is not\nthe syllogism, but the *relation to \u201cvalues.\u201d* So far as the single\nhistorical facts can be related to values, they are of historical\nimportance, and in such a way only does history in its proper sense\nbecome important in itself and through itself at the same time. Must\nhistory always lose its historical aspect to become of importance to\nhuman knowledge? That is the question we asked whilst considering the\ngeneral logical types of the \u201cevolution\u201d and \u201ccumulation\u201d that arose out\nof the analysis of the historical facts of problematic phylogeny. It\nnow might seem that this question may be answered, and that it may be\nanswered by a clear and simple \u201cNo.\u201d The history of mankind, according\nto Rickert, seems to be important in itself, and without borrowing from\nany other branch of study. But is his reasoning altogether cogent and\nconvincing?\n\nHas it really been able to attribute to history in the strictest sense\nsuch an importance for philosophy, for the theory of the universe, \u201cf\u00fcr\ndie Weltanschauung,\u201d that history proper may in fact be allowed to take\nits place beside science proper?\n\nThe relation to values is not to include any kind of \u201cBewertung\u201d of\njudgment, Rickert allows. In fact, history of any kind would hardly\nsatisfy the reader, if moral judgment were its basis. Every reader, of\ncourse, has a moral judgment of his own, but, unfortunately, almost\nevery reader\u2019s judgment is different from his neighbour\u2019s, and there\nis no uniformity of moral principles as there is of geometrical ones.\nWe shall come back to this point. At present we only state the fact\nthat indeed moral judgment can never be the foundation of history, and\nthat Rickert was very right to say so: it is enough to put the names\nof Tolstoy and Nietzsche together to understand how devoid of even\nthe smallest general validity would be a history resting upon moral\nprinciples.\n\nBut what then are the \u201cvalues\u201d of Rickert to which history has to\nrelate, if moral values in their proper sense have to be excluded? It is\nhere that his discussions begin to become obscure and unsatisfactory,\nand the reason is fairly intelligible. He is trying to prove the\nimpossible; he wants to put history beside science in its real\nphilosophical importance, in spite of the fact that all evidence to\nestablish this is wanting.\n\nThese \u201cvalues,\u201d to which every historical act in its singularity has to\nbe related in order to become an element of real history, are they after\nall nothing but those groups of the products of civilisation which in\nfact absorb the interest of men? Is it to groups of cultural phenomena,\nsuch as arts, science, the State, religion, war, economics, and so on,\nthat \u201chistorical\u201d facts have to be related? Yes, as far as I understand\nour author, it is simply to these or other even less important groups\nof cultural effects--cultural \u201ccumulations,\u201d to apply our term--that a\nsingle action of a man or a group of men must bear some relation in\norder to become important historically.\n\nBut what does that mean? Is the relation to such \u201cvalues\u201d to be\nregarded as really rendering history equal to the sciences of nature in\nphilosophical importance?\n\nIn the first place, there is no more agreement about such \u201cvalues\u201d than\nthere is in the field of morals. Imagine, for instance, a religious\nenthusiast or recluse writing history! I fancy there would be very\nlittle mention of warriors and politicians: war and politics would\nnot be \u201cvalues\u201d in *any* sense to such a man. And we know that there\nare others to whom those products of civilised life rank amongst the\nfirst. Rickert well notes that there is one great objection to his\ndoctrine--the character of universality[167] is wanting to his history,\nor rather to the values forming its basis; for there cannot be, or at\nleast there actually is not at present, a *consensus omnium* with regard\nto these \u201cvalues.\u201d\n\n[167] The word \u201cuniversality\u201d to be understood here in quite an\nunpretentious quasi-popular meaning, not strictly epistemologically.\n\nI am convinced that Rickert is right in his conception of real \u201chistory\u201d\nas the knowledge of the single acts of mankind. But this conception\nproves just the contrary of what Rickert hoped to prove; for history in\nthis sense is moulded by the actual products of culture, that is, by\nthe effects which actually exist as groups of cultural processes, and\nit cannot be moulded by anything else; the historian correlates history\nwith what *interests* him personally.\n\nHere now we have met definitively the ambiguous word: history indeed\nis to end in \u201cinterest\u201d and in being \u201cinteresting.\u201d There is nothing\nlike a real \u201cvalue\u201d in any sense underlying history; the word *value*\ntherefore would better give place to the term \u201ccentre of interest\u201d--a\ncollection of stamps may be such a \u201ccentre.\u201d History, then, as the\nknowledge of cultural singularities, is \u201cinteresting,\u201d and its aspects\nchange with the interests of the person who writes history: there is no\ncommonly accepted foundation of history.[168]\n\n[168] To avoid mistakes I wish to say here most emphatically that,\naccording to Rickert, the method of history is regarded as completely\n*free* from subjectivity as soon as its \u201cvalues\u201d are once *established*.\nBut this cannot avail to save the theory.\n\nAnd it follows that history as regarded by Rickert cannot serve as\nthe preliminary to philosophy. It *may* be[169] of use for personal\nedification or for practical life: granting that the \u201ccentres of\ninterest\u201d as referred to are of any real ethical or at least factual\nimportance. But you may take away from history even the greatest\npersonalities, and your view of the universe, your philosophy, would\nremain the same, except of course so far as these personalities\nthemselves have contributed to philosophy in any way.\n\n[169] This is a rather optimistic conception of \u201chistory.\u201d Personally, I\nmust confess that even its emotional and practical importance seems to\nme to be at least diminished by the retarding effects which all sorts\nof \u201chistorical\u201d considerations--in science as well as in arts and in\npublic life--carry with them. All real progress is non-historical--and\nits champions almost always have become martyrs: this fact seems not to\nrecommend history as a means of education, except for persons of a very\nstrong character.\n\nNow, on the other hand, it is worth noticing that, even if there were\ngenerally accepted \u201cvalues,\u201d history as the doctrine of singularities\nwould be deprived of philosophical importance. Its single cases would\nthen be merely *instances* of certain types of actions and occurrences\nwhich have been proved to be \u201cvaluable,\u201d *i.e.* to be centres of\ninterest, before-hand. Rickert has observed that the relation to\nany judgments about moral values would render history unhistorical,\nfor the generalities to which it is related would be the main thing\nin such a case. But he did not notice, as far as I can see, that\nhistory, if related to *any* \u201cvalues\u201d whatever--if there were any\ngenerally conceded--would become \u201cnon-historical\u201d just as well: for the\n*generalities* as expressed in the \u201cvalues\u201d would be the main thing in\nthis case also. In fact, there is no escape from the dilemma:--either no\ngeneral centres of interest, and therefore a mere subjective \u201chistory\u201d;\nor general \u201cvalues,\u201d and therefore history a mere collection of\ninstances.\n\nThe \u201climits of concepts in natural sciences\u201d then are the same as the\nlimits of *intellectual* concepts in general. For intellectual, *i.e.*\nlogical, \u201cvalues\u201d are the only centres of interest that can lay claim\nto universality. There are indeed other groups of important concepts,\nthe ethical ones, but they are outside intellectuality and may enter\nphilosophy only as problems, not as solutions. Therefore, history in\nits true sense, even if related to the ethical group of concepts,\nhas no bearing on philosophy. Philosophically it remains a sum of\ncontingencies, in which certain laws of cumulation and certain series of\ncumulation may be discovered. But these series and these laws, if taken\nscientifically, only offer us instances of psychological elementalities.\nThey also might be instances of primary ethical states and relations, if\nthere were such relations of more than a mere subjective and personal\nvalidity, which at present at least seems not to be the case.\n\n\n\n\nCONCLUSIONS ABOUT SYSTEMATICS AND HISTORY IN GENERAL\n\n\nWe have finished our analysis of the history of mankind as the only\ninstance of an historical biological process that is actually known to\nexist and is not only assumed hypothetically.\n\nWhat we have learnt from this analysis, though certainly important in\nitself, has not afforded us any new result for theoretical biology.\n\nThe history of mankind is proved to be of philosophical importance,\nat present, so far only as it offers instances to the science of\npsychology; besides that it may be of value and importance to many\nconditions of practical and emotional life.\n\nThere is only one science, and only one kind of logic too. \u201cIn one sense\nthe only science\u201d--that was the predicate attached to natural sciences\nby Lord Gifford, as you will remember from our first lecture. It is not\nwithout interest to note that at the end of our course of this year,\nwe find occasion to realise on what a deep insight into logical and\nphilosophical relations that sentence was grounded.\n\nWe now leave the theory of human history, which has been to us nothing\nmore than a branch of biological phylogeny in general. We have dealt\nwith it from quite a simple realistic point of view, not burdened by any\nepistemology. We have taken psychical states as realities, just as we\nhave taken as realities all parts of the animal body; and it seems to\nme that we were entitled to do so, as it was only history *about* the\nactions of men we were dealing with, not their actions themselves. Next\nsummer we shall begin with studying action as action, and then, in fact,\na well-founded epistemology will be among our first requirements. And\nhistory also will come on the scene once more.\n\nIt is the main result of our last chapters, devoted to systematics,\ntransformism, and human history in particular, that no conclusions\nreally useful for further philosophical discussion can at present be\ngained from these topics; there either is too little actual knowledge,\nor there are only combinations of natural elementalities, but no\nelementalities of any new kind.\n\nTo sum up: we expected that a rational system might be a biological\nresult of the future, but we could not claim at all to possess such a\nsystem. We said that transformism might be proved one day to be a true\nevolution, governed by one immanent principle, which then would have to\nbe regarded as a new primary factor in nature, but we did not know the\nleast about that principle.\n\nHuman history, on the other hand--that is, the only historical process\nconcerned with life that is actually known to have occurred--could not\nteach us anything of an elemental character, since human history, at\npresent at least, did not appear to us as a true evolution, but only as\na sum of cumulations, and the singularities of this history, taken by\nthemselves, could only be of practical or emotional interest.\n\nThus it is from the study of the living *individual* only, that we\nhave so far gained elemental principles in biology. The analysis of\nindividual morphogenesis and of individual inheritance has yielded\nus the concept of entelechy as the chief result of the first part of\nour lectures. We shall be able to get more proofs of the autonomy of\nthe individual life in the beginning of the second part; indeed, the\nbeginning of that part will bring us to a full understanding of what the\nliving individual is, and what it is not. And then the real philosophy\nof life, that is, the philosophy of the individual, will occupy us for\nthe greater half of our lectures of next summer.\n\n\n\n\nINDEX\n\n\n  Absolute, 5\n\n  Acclimatisation, 191\n\n  Acquired characters, 217, 276 f.\n\n  Adaptation (definition), 166, 171, 185\n    to changes from without, 172 ff.\n    functional, 114, 176 ff.\n    and Lamarckism, 272, 280\n    mechanical, 177 f.\n    morphological, 168 ff.\n    physiological, 184 ff.\n    primary and secondary, 188 f.\n\n  Adaptedness, 186 f.\n\n  *Adiantum*, 279\n\n  Adventitious, 55, 74, 111, 221\n\n  Albumen, 200\n\n  Allelomorphs, 231\n\n  Amphibious plants, 172 ff.\n\n  Annelids, 65, 70, 221\n\n  Answering reaction, 181\n\n  Anti-bodies, 206 f.\n\n  Antitoxins, 207 f.\n\n  *A priori*, 6\n\n  Aristotle, 144\n\n  *Ascaris*, 93\n\n  *Aspergillus*, 195\n\n  Assimilation, 17\n\n  Atrophy, 178\n\n  Autonomy of life, 143, 224 f., 324\n\n\n  Bab\u00e1k, 177\n\n  Baer, C. E. v., 48 f. 282\n\n  Bateson, 229 ff., 238\n\n  Bayliss, 204, 212\n\n  *Begonia*, 221\n\n  Bergson, 305\n\n  Berkeley, 6\n\n  Berthold, 91\n\n  Biogenetisches Grundgesetz, 248\n\n  Biology, 8 ff., 15 f.\n\n  Blaringhem, 238, 276\n\n  Blastoderm, 39\n\n  Blastomeres, 36, 59, 61 f., 79\n\n  Blastula, 37, 61, 79\n\n  Blumenbach, 26\n\n  Boirivant, 174\n\n  Bonnet, 26\n\n  Boveri, 29, 60, 95, 235 f.\n\n  Buckle, 308, 310\n\n  Bunge, v., 248\n\n  B\u00fctschli, 91\n\n\n  Calcium, 97\n\n  Calkins, 33\n\n  Cambium, 120, 183, 220\n\n  Catalysis, 164, 203\n\n  Categories, 6 f.\n\n  Cause, 99 ff.\n\n  Cell, 27 f.\n    -division, 28 ff., 53, 94\n    -lineage, 58, 70\n    -theory, 27 f.\n\n  Chemical theory (of morphogenesis), 134 ff.\n\n  Chemistry, systematics of, 244.\n\n  Child, C. M., 180\n\n  Chromatic regulations, 197\n\n  Chromatin, 28 f.\n\n  Chromosomes, 30, 237\n\n  Chun, 66\n\n  Classification, 246 f.\n\n  *Clavellina*, 129, 154, 162 f.\n\n  Cleavage, 35 ff., 53, 58, 60, 63, 71, 92\n\n  Colloids, 187\n\n  Compensatory process, 112\n\n  Complex potencies, 112, 120\n\n  Conic sections, 243\n\n  Conjugation, 33\n\n  Conklin, 86\n\n  Contingency, 218, 284 ff. 304\n\n  Continuity of germ-plasm, 215, 227\n\n  Cope, 273\n\n  Correlation (of masses), 93\n    (of parts), 247\n\n  Correns, 228\n\n  Crampton, 70 f.\n\n  Crayfish, 105\n\n  Ctenophores, 66\n\n  Cumulation, 301 ff., 308 ff., 314, 317\n\n  Cuvier, 247\n\n\n  Darwin, Ch., 260 ff., 271, 283\n\n  Darwinism, 260 ff., 271, 283 ff., 293 ff., 304\n\n  Davenport, 191, 206\n\n  Delage, 32\n\n  Descent, theory of, 250 ff.\n\n  Description, 12, 50\n\n  Detto, 172\n\n  Directive stimuli, 102 ff.\n\n  Doncaster, 232\n\n  Dreyer, 92\n\n\n  *Echinus*, 27, 33 ff., 60 ff., 68, 81, 85, 87,\n    98, 104, 108, 111, 154, 232, 235\n\n  Ectoderm, 41, 81, 122\n\n  Egg, 31, 33 f.\n\n  Ehrlich, 207 f.\n\n  Eimer, 292\n\n  Elementary organs, 46 ff.\n    processes, 46 ff.\n\n  Elements of nature, 9\n\n  Embryo, 44\n    frog\u2019s, 59, 65, 67\n    half, 59, 61, 66 ff.\n    whole, 61, 67 f.\n\n  Endoderm, 41, 81\n\n  Entelechy, 143 f., 224 f., 295\n\n  Entwickelungsmechanik, 57, 70, 78, 241\n\n  Enumeration, 297, 300\n\n  Enzymes, 164, 203\n\n  Epigenesis, 26, 45, 54, 72, 144, 301\n\n  Equifinality (of restitutions), 159 f.\n\n  Equipotential, 83\n\n  Eschenhagen, 195\n\n  Evolutio, 26, 45 f., 54, 59, 61, 64, 72, 144, 205, 301\n\n  Evolution, 8, 21, 46, 250, 301, 305, 311 ff., 317\n\n  Experience, 7 f., 12, 212\n\n  Experiment, 51, 56 f.\n\n  \u201cExplaining,\u201d 51, 309\n\n  Explicit potency, 84\n\n\n  Fasting, 199 f.\n\n  Ferments, 164, 203 f.\n\n  Fertilisation, 32 ff.\n\n  Fischer, 278\n\n  Foges, 107\n\n  Form, closed or open, 49\n\n  Form, organic, specific, 16 ff., 25, 92, 293 ff.\n\n  Forma accidentalis, 293\n    essentialis, 294 f.\n\n  Formative stimuli, 102 ff., 113, 118, 133\n\n  Franc\u00e9, 158, 239\n\n  Fr\u00e9d\u00e9ricq, 196\n\n  Frog, embryo of, 59, 65, 67\n\n  Fromm, 205\n\n  Function (mathematical), 80\n\n  Fungi, metabolism of, 201\n\n\n  Gaidukow, 197 f.\n\n  Galls, 101\n\n  Galton, 228, 238\n\n  Gamble and Keeble, 198\n\n  Gastrula, 41, 61, 81\n\n  Gautier, 239\n\n  Geographical distribution, 251 f.\n\n  Geometry, solid, 243\n\n  Germ-layers, 41, 44, 61\n    -lineage, 215\n    -plasm, 52, 215\n\n  Gifford, Lord, 1 ff., 322\n\n  Godlewski, 105, 155, 235\n\n  Goebel, 116\n\n  Goethe, 247\n\n  Goette, 48, 56, 214\n\n  Goltz, 181\n\n  Growth, 30, 93 f.\n\n  Gruber, 236\n\n\n  Haeckel, 37, 41\n\n  Half-embryo, 59, 61, 66 ff.\n\n  Haller, A. v., 26\n\n  Harmony, 107 ff., 117, 295\n\n  Hausmann, 206\n\n  Heat production, 193\n\n  Hegel, 307, 311 ff.\n\n  Herbst, 96 ff., 102, 104 ff., 172, 177, 200, 232, 236\n\n  Heredity, 21, 52\n\n  Hering, 216 f.\n\n  Hertwig, O., 60, 65\n\n  Hertwig, R., 32 f., 60, 107\n\n  His, 56, 93\n\n  History, 2, 14, 21, 250, 257, 297 ff.\n    of mankind, 306 ff.\n\n  Holmes, 180\n\n  Hume, 6\n\n  Hypertrophy, 112, 114\n\n  Hypertypy, 112\n\n\n  Idealism, 5, 7\n\n  Immunity, 204 ff.\n\n  Implicit potency, 84\n\n  Improvement (of morphogenesis), 212\n\n  Indifferent cells, 182\n\n  Inflammation, 206\n\n  Inheritance, 35, 214 ff.\n    of acquired characters, 217, 275 ff., 290\n\n  Irritability, 190 ff.\n\n\n  Jacoby, 207\n\n  Jaeger, 214\n\n  Jennings, 218\n\n\n  Kammerer, 176, 280\n\n  Kant, 6 f.\n\n  Kirchhoff, 50\n\n  Klebs, 96, 170, 180, 238, 276\n\n  K\u00f6lliker, 292\n\n  Korshinsky, 239\n\n  Kra\u0161an, 221, 251\n\n\n  Lamarck, 271 f., 291\n\n  Lamarckism, 271 f., 284 ff., 293 ff., 304\n\n  Lamprecht, 308, 310\n\n  Larva, 41 f., 44\n\n  Law of nature, 13, 16\n\n  Leibniz, 6\n\n  Lens (of eye), 105, 221\n\n  Liebmann, 256\n\n  Life, 9 f., 16, 21\n\n  Lillie, R. S., 236\n\n  Limits of regulability, 212\n\n  Lithium, 99\n\n  \u201cLiving,\u201d 9, 16\n\n  Localisation, 101, 103, 118 ff.\n\n  Locke, 6\n\n  Loeb, J., 32, 102, 164, 179, 196, 236\n\n  Loeb, L., 208\n\n  Lyon, 87\n\n\n  MacDougal, 238 f., 276\n\n  Machine (definition), 139\n\n  Machine-theory of life, 138 ff., 187, 210\n\n  Maillard, 196\n\n  Manifoldness, 25 f., 30, 45\n    intensive, 144\n\n  Materialism, 283\n\n  Materials, transport of, 194\n\n  Matter, theory of, 8\n\n  Maturation, 31, 87\n\n  Mayenburg, v., 195\n\n  Means, of morphogenesis, 89 ff., 101, 113, 118, 228, 234\n\n  Memory, 216 f.\n\n  Mendel, 229 f.\n\n  Merrifield, 198\n\n  Mesenchyme, 39, 41, 104, 111, 151 f.\n\n  Metabolic regulations, 198 f.\n\n  Metabolism, 16, 184\n    of fungi, 201\n\n  Metschnikoff, 206\n\n  Micromeres, 36, 60\n\n  Miehe, 116\n\n  Mill, J. S., 57\n\n  *Mimosa*, 191\n\n  Minkiewicz, 198\n\n  Modification, 277\n\n  Molluscs, 70 f., 86\n\n  Morgan, T. H., 32, 66 f., 95, 107, 114 f., 162, 230\n\n  Morphaesthesia, 157\n\n  Morphogenesis, 20, 52, 76, 112, 118 f.\n\n  Morphology, 12\n\n  Movements, organic, 17\n\n  Mutations, 237 f., 276, 291\n\n\n  N\u00e4geli, 266, 292\n\n  Nathansohn, 196\n\n  Natural selection, 261 f., 290\n\n  Nature, 5 ff.\n\n  N\u011bmec, 116\n\n  Newport, 57\n\n  Newt (regeneration of), 155, 221 f.\n\n  Noll, 146, 157 f.\n\n  Nomothetic, 14 f.\n\n  Normal, 78\n\n  Nuclear division, 28 f., 62, 64 f., 72, 235\n\n  Nucleus, 28, 35\n    r\u00f4le of nucleus in inheritance, 233 f.\n\n\n  Organ-forming substances, 117\n\n  *Oscillariae*, 197\n\n  Osmotic pressure, 93, 187, 194 f.\n\n  Overton, 196 f.\n\n  Oxidation, r\u00f4le of, 198 f.\n\n\n  Palaeontology, 252\n\n  Parallelism (psycho-physical), 146\n\n  Parthenogenesis, 32\n\n  Pauly, 146, 217, 273 f.\n\n  Pawlow, 204, 210, 212\n\n  Pearl, R., 212\n\n  Pfeffer, 195, 201\n\n  Phagocytosis, 206\n\n  Phenomenon, 5 f.\n\n  Philosophy, natural, 4\n    of nature, 4, 7, 9\n    of the organism, 9, 15\n\n  Phylogeny, 255, 291, 297, 304 ff.\n\n  Physiology, 12\n    of development (morphogenesis), 20\n\n  *Planaria*, 130, 155, 162 f., 200\n\n  Plants, 48 f.\n\n  Plato, 2\n\n  Pluteus, 42\n\n  Poisons, 205 ff.\n\n  Pole, 36\n\n  Polarity, 106\n\n  Potencies, complex, 112, 120\n    explicit, 84\n    implicit, 84\n    primary, 84, 111\n    prospective, 77 ff., 83, 89, 118, 125, 241\n    secondary, 84, 110\n\n  Poulton, 198\n\n  Precipitin, 207 f.\n\n  Pressure experiments, 63, 141\n\n  Primary potency, 84, 111\n    purposefulness, 146, 287\n    regulation, 85, 174, 188\n\n  Progress, 305\n\n  Pronuclei, 55\n\n  Prospective potency, 77 ff., 83, 89, 118, 125, 241\n    value, 77 f., 80, 122\n\n  Protista (Protozoa), 27, 130, 236\n\n  Protoplasm, 28, 30\n    morphogenetic r\u00f4le of, 67\n\n  Przibram, 112, 248\n\n\n  R\u00e1dl, 247\n\n  Rauber, 235\n\n  Reaction, answering, 181\n\n  Reciprocity of harmony, 156 f.\n\n  Re-differentiation, 75, 111, 163\n\n  Regeneration, 55, 74, 105, 111, 221\n    super-, 115 f.\n\n  Regulation, 68, 73, 85, 111, 165\n    defined, 166\n    metabolic, 198 f.\n    secondary, 85, 165, 188\n\n  Reinke, 146\n\n  Restitution, 21, 74, 110, 112 ff.\n    defined, 166\n    and Darwinism, 267\n    and Lamarckism, 286\n    of second order, 158\n\n  Retina, 191\n\n  Retro-differentiation, 163 f.\n\n  Rhumbler, 93\n\n  Ribbert, 114\n\n  Rickert, 315 ff.\n\n  Roux, 26, 48, 55 ff., 66 f., 76, 89, 92 f., 108, 161, 176 f., 241\n\n  Rubner, 193\n\n\n  Sachs, 117\n\n  Sadebeck, 279\n\n  *Salamandra*, 175, 281\n\n  Schneider, 146\n\n  Schultz, E., 200\n\n  Schultze, O., 67\n\n  Schwendener, 177\n\n  Science, 14, 297\n    natural, 1 ff.\n    rational, 12\n\n  Sea-urchin, *see* Echinus\n\n  Secondary potency, 84, 110\n    regulation, 85, 165, 188\n\n  Secretion, internal, 116, 200\n\n  Segmentation, 35\n\n  Selective qualities (of tissues), 186\n\n  Self-differentiation, 108\n\n  Semon, 216 f.\n\n  Sex, 107\n\n  Single, the, 315 ff.\n\n  Skeleton, 40 ff., 44, 47, 92\n\n  Spemann, 105\n\n  Spermatozoon (spermia), 32 ff.\n\n  Splitting (of hybrids), 229 f.\n\n  Stahl, 197\n\n  Standfuss, 278\n\n  Starfish, 44, 81, 122\n\n  Starling, E., 116, 204, 212\n\n  *Stentor*, 131\n\n  Stimuli, directive, 102 ff.\n    formative, 102 ff., 113, 118, 133\n    of restitutions, 113 f.\n\n  Structure of protoplasm, 66, 69, 72 f. 85, 88\n\n  Substance, living, 17\n\n  Sumner, 196\n\n  Super-regeneration, 115 f.\n\n  Surface-tension, 91\n\n  Sutton, 230\n\n  Symmetry, 39, 68, 70, 72, 89, 98\n\n  System, combined types of, 153 ff.\n    complex, 219 f.\n    complex-harmonious, 155\n    equipotential, 120\n    harmonious-equipotential, 121 ff., 151 f.\n    mixed-equipotential, 154\n    morphogenetic, 119 f., 163, 241\n\n  Systematics, 14 ff., 21, 243 f., 253, 264, 293, 296\n\n\n  Taine, 308, 310\n\n  Theology, natural, 1 ff.\n\n  Thomson, J. A., 16\n\n  Thymus, 204\n\n  Thyroid, 204\n\n  Tissue, 38\n\n  Toxins, 207 f.\n\n  Transformism, 251\n\n  Truth, 7\n\n  Tschermak, 228\n\n  *Tubularia*, 126 ff., 133, 158 ff.\n\n  Type, 48, 247 f., 282, 291\n\n\n  \u201cUnderstanding\u201d (historically), 302\n\n  Universality, postulate of, 148 f.\n\n  Universe, 5\n\n  Univocality, principle of, 161\n\n\n  \u201cValues,\u201d 317 ff.\n    prospective, 77 f., 80, 122\n\n  Variation, 218, 237 f., 276\n\n  Variation, fluctuating, contingent, 264 f., 273 f., 282, 290\n\n  Vernon, 232, 238\n\n  Vitalism, 143, 145 f., 210 f., 224 f., 234, 240 f., 272, 277\n\n  V\u00f6chting, 174, 179 f., 182, 221\n\n  Volition, acts of, 274\n\n  Vries, de, 228, 238 f.\n\n\n  Wallace, 292\n\n  Ward, J., 8, 143\n\n  Weber, law of, 191\n\n  Weinland, 202\n\n  Weismann, 33, 52 ff., 58 f., 72, 74 f., 103,\n    111, 138, 214 f., 237, 277 f.\n\n  Weldon, 238\n\n  Whole, the, 28, 80, 117\n    -embryo, 61, 67 f.\n\n  Wigand, 255, 266, 292\n\n  Wilson, E. B., 27, 65, 70 f., 86 f., 107\n\n  Windelband, 13 f.\n\n  Winkler, 116, 221\n\n  Winterstein, 199\n\n  Wolff, C. F., 26\n\n  Wolff, G., 105, 146, 255, 266, 287 f.\n\n  Wolff, J., 177\n\n\n  Yung, 177\n\n\n  Zeleny, 112, 115, 212\n\n  Zur Strassen, 93\n\n\n                                THE END\n\n           *Printed by* R. & R. CLARK, LIMITED, *Edinburgh*.\n\n\n\n\n                         HEREDITY AND SELECTION\n                              IN SOCIOLOGY\n\n\n                                   BY\n\n                           G. CHATTERTON HILL\n\n                      Demy 8vo, Cloth, 600 pages.\n\n                         Price =12s. 6d.= net.\n\n                     *Post Free, Price* =12s. 11d.=\n\n                          SOME PRESS OPINIONS\n\n\u201cA most praiseworthy and suggestive work--should certainly be studied by\nevery serious thinker.\u201d--*Morning Post.*\n\n\u201cMr. Hill is decidedly doctrinaire, but his book is packed with\nscientific and sociological facts, and it gives the reader healthy\nintellectual exercise.\u201d--*Christian World.*\n\n\u201cShows wide reading, is written in a forcible and clear style, and\ncontains much that is interesting, fresh, and acute.\u201d--*Aberdeen Free\nPress.*\n\n\u201cIt is a book of equal calibre with Mr. Kidd\u2019s and goes even deeper\nthan that remarkable production into the springs of life and\nconduct.\u201d--*Methodist Recorder.*\n\n\u201cThis most suggestive and valuable work, which contains abundant\nsociological data.\u201d--*Aberdeen Journal.*\n\n\u201cMr. George Chatterton Hill has written a volume of surpassing interest\nnot alone to scientific but to theological students.\u201d--*Catholic Times.*\n\nPublished by A. & C. BLACK, SOHO SQUARE, LONDON, W.\n\n\n\n\n                            RUDOLF EUCKEN\u2019S\n                           PHILOSOPHY OF LIFE\n\n                                   BY\n\n                           W. R. BOYCE GIBSON\n\n           LECTURER IN PHILOSOPHY IN THE UNIVERSITY OF LONDON\n\n                             SECOND EDITION\n\n     Crown 8vo, Cloth, with Frontispiece Portrait of Rudolf Eucken.\n\n                          Price =3s. 6d.= net.\n\n                     *Post Free, Price* =3s. 10d.=\n\n                          SOME PRESS OPINIONS\n\n\u201cMr. Gibson has given us in small compass a lucid exposition of the\nphilosophical system of Eucken, who is Professor of Philosophy in\nJena.... This is a most suggestive and stimulating book. In a very\nreal sense it has brought philosophy down to earth and is deserving of\nserious study.\u201d--*Aberdeen Free Press.*\n\n\u201cTo it the interested reader will turn with expectation, and his\nexpectation is likely to be more than realised. For Dr. Boyce Gibson\nis himself a scholar, as well as an enthusiastic lover of this great\nscholar.\u201d--*Expository Times.*\n\n\u201cNo reader should fail to find pleasure in a book so full of fresh and\nstimulating thought, expressed with great felicity of language.\u201d--*The\nScottish Review.*\n\n\u201cIt is done with just the proper combination of sympathy and\ncriticism.\u201d--*British Weekly.*\n\n\u201cThis little book on Eucken\u2019s Philosophy is of quite exceptional\ninterest and importance.\u201d--*The Inquirer.*\n\n\u201cProfessor Boyce Gibson ... has performed a real service in promoting\nthe acquaintance of English, and American students with a thinker whose\ndistinctive views give him a special claim to their attention....\nProfessor Gibson has achieved a notable success, writing briefly,\nlucidly, and sympathetically.\u201d--*The New Age.*\n\n\nPublished by A. & C. BLACK, SOHO SQUARE, LONDON, W.","title":"The Science and Philosophy of the Organism","tradition":"philosophy-ethics","translated_text":null,"word_count":91911}