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Title: The Science and Philosophy of the Organism - The Gifford Lectures Delivered Before the University of - Aberdeen in the Year 1907
Author: Driesch, Hans
Language: English
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relevant text for greater clarity.

THE SCIENCE AND PHILOSOPHY
OF THE ORGANISM

AGENTS

America The Macmillan Company
64 & 66 Fifth Avenue, New York

Australasia The Oxford University Press, Melbourne

Canada The Macmillan Company of Canada, Ltd.
27 Richmond Street West, Toronto

India Macmillan & Company, Ltd.
Macmillan Building, Bombay
309 Bow Bazaar Street, Calcutta

THE
SCIENCE AND PHILOSOPHY
OF THE ORGANISM

THE GIFFORD LECTURES DELIVERED BEFORE
THE UNIVERSITY OF ABERDEEN
IN THE YEAR 1907

BY
HANS DRIESCH, Ph.D.
HEIDELBERG

LONDON
ADAM AND CHARLES BLACK
1908

PREFACE

This work is not a text-book of theoretical biology; it is a systematic
presentment of those biological topics which bear upon the true
philosophy of nature. The book is written in a decidedly subjective
manner, and it seems to me that this is just what “Gifford Lectures”
ought to be. They ought never to lose, or even try to lose, their
decidedly personal character.

My appointment as Gifford Lecturer, the news of which reached me in
February 1906, came just at the right moment in the progress of my
theoretical studies. I had always tried to improve my previous books by
adding notes or altering the arrangement; I also had left a good deal of
things unpublished, and thus I often hoped that I might have occasion
to arrange for a new, improved, and enlarged edition of those books.
This work then is the realisation of my hopes; it is, in its way, a
definitive statement of all that I have to say about the Organic.

The first volume of this work, containing the lectures for 1907--though
the division into “lectures” has not been preserved--consists of Parts
I. and II. of Section A, “The Chief Results of Analytical Biology.”
It gives in Part I. a shortened, revised, and, as I hope, improved
account of what was published in my *Analytische Theorie der organischen
Entwickelung* (1894), *Die Localisation morphogenetischer Vorgänge;
ein Beweis Vitalistischen Geschehens* (1899), and *Die organischen
Regulationen* (1901), though for the professed biologist the two
last-named books are by no means superseded by the new work. Part II.
has never been published in any systematic form before, though there are
many remarks on Systematics, Darwinism, etc., in my previous papers.

The second volume--to be published in the autumn, after the delivery of
the 1908 lectures--will begin with the third and concluding part of the
scientific section, which is a very carefully revised and rearranged
second edition of my book, *Die “Seele” als elementarer Naturfactor*
(1903). The greater part of this volume, however, will be devoted to the
“Philosophy of the Organism,” *i.e.* Section B, which, in my opinion,
includes the most important parts of the work.

Some apology is needed for my presuming to write in English. I was
led to do so by the conviction, mistaken perhaps, that the process of
translation would rob the lectures of that individual and personal
character which, as I said before, seems to me so much to be desired. I
wished nothing to come between me and my audience. I accordingly wrote
my manuscript in English, and then submitted it to linguistic revision
by such skilled aid as I was able to procure at Heidelberg. My reviser
tells me that if the result of his labours leaves much to be desired,
it is not to be wondered at, but that, being neither a biologist nor a
philosopher, he has done his best to make me presentable to the English
reader. If he has failed in his troublesome task, I know that it is not
for want of care and attention, and I desire here to record my sense of
indebtedness to him. He wishes to remain anonymous, but I am permitted
to say that, though resident in a foreign university, he is of Scottish
name and English birth.

My gratitude to my friends at Aberdeen, in particular to Professor and
Mrs. J. A. Thomson, for their hospitality and great kindness towards me
cannot be expressed here; they all know that they succeeded in making me
feel quite at home with them.

I am very much obliged to my publishers, Messrs. A. and C. Black, for
their readiness to fulfil all my wishes with respect to publication.

The lectures contained in this book were written in English by a
German and delivered at a Scottish university. Almost all of the ideas
discussed in it were first conceived during the author’s long residence
in Southern Italy. Thus this book may be witness to the truth which,
I hope, will be universally recognised in the near future--that all
culture, moral and intellectual and aesthetic, is not limited by the
bounds of nationality.

HANS DRIESCH.

Heidelberg, *2nd January 1908*.

CONTENTS OF THE FIRST VOLUME

THE PROGRAMME

PAGE
On Lord Gifford’s Conception of “Science” 1
Natural Sciences and “Natural Theology” 3
Our Philosophical Basis 5
On Certain Characteristics of Biology as a Science 9
The Three Different Types of Knowledge about Nature 13
General Plan of these Lectures 15
General Character of the Organic Form 19

SECTION A.--THE CHIEF RESULTS OF ANALYTICAL BIOLOGY

PART I.--THE INDIVIDUAL ORGANISM WITH REGARD TO FORM AND METABOLISM

*A.* ELEMENTARY MORPHOGENESIS--

Evolutio and Epigenesis in the old Sense 25
The Cell 27
The Egg: its Maturation and Fertilisation 31
The First Developmental Processes of Echinus 33
Comparative Embryology 44
The First Steps of Analytical Morphogenesis 45
The Limits of Pure Description in Science 50

*B.* EXPERIMENTAL AND THEORETICAL MORPHOGENESIS--

1. THE FOUNDATIONS OF THE PHYSIOLOGY OF DEVELOPMENT.
“EVOLUTIO” AND “EPIGENESIS” 52

The Theory of Weismann 52
Experimental Morphology 56
The Work of Wilhelm Roux 58
The Experiments on the Egg of the Sea-urchin 59
On the Intimate Structure of the Protoplasm of the Germ 65
On some Specificities of Organisation in Certain Germs 70
General Results of the First Period of “Entwickelungsmechanik” 71
Some New Results concerning Restitutions 74

2. ANALYTICAL THEORY OF MORPHOGENESIS 76

α. THE DISTRIBUTION OF MORPHOGENIC POTENCIES 76

Prospective Value and Prospective Potency 76
The Potencies of the Blastomeres 79
The Potencies of Elementary Organs in General 80
Explicit and Implicit Potencies: Primary and Secondary
Potencies 83
The Morphogenetic Function of Maturation in the Light of
Recent Discoveries 85
The Intimate Structure of Protoplasm: Further Remarks 88
The Neutrality of the Concept of “Potency” 89

β. THE “MEANS” OF MORPHOGENESIS 89

β′. The Internal Elementary Means of Morphogenesis 90

Some Remarks on the Importance of Surface Tension in
Morphogenesis 91
On Growth 93
On Cell-division 94

β″. The External Means of Morphogenesis 95

The Discoveries of Herbst 96

γ. THE FORMATIVE CAUSES OR STIMULI 99

The Definition of Cause 99
Some Instances of Formative and Directive Stimuli 102

δ. THE MORPHOGENETIC HARMONIES 107

ε. ON RESTITUTIONS 110

A few Remarks on Secondary Potencies and on Secondary
Morphogenetic Regulations in General 110
The Stimuli of Restitutions 113

3. THE PROBLEM OF MORPHOGENETIC LOCALISATION: THE
THEORY OF THE HARMONIOUS-EQUIPOTENTIAL SYSTEM--FIRST
PROOF OF THE AUTONOMY OF LIFE 118

The General Problem 118
The Morphogenetic “System” 119
The “Harmonious-equipotential System” 122
Instances of “Harmonious-equipotential Systems” 126
The Problem of the Factor *E* 132
No Explanation offered by “Means” or “Formative Stimuli” 132
No Explanation offered by a Chemical Theory of Morphogenesis 134
No Machine Possible Inside the Harmonious Systems 138
The Autonomy of Morphogenesis proved 142
“Entelechy” 143
Some General Remarks on Vitalism 145
The Logic of our First Proof of Vitalism 146

4. ON CERTAIN OTHER FEATURES OF MORPHOGENESIS ADVOCATING
ITS AUTONOMY 150

Harmonious-equipotential Systems formed by Wandering Cells 151
On Certain Combined Types of Morphogenetic Systems 153
The “Morphaesthesia” of Noll 157
Restitutions of the Second Order 158
On the “Equifinality” of Restitutions 159
Remarks on “Retro-Differentiation” 163

*C.* ADAPTATION--

INTRODUCTORY REMARKS ON REGULATIONS IN GENERAL 165

1. MORPHOLOGICAL ADAPTATION 168

The Limits of the Concept of Adaptation 168
Adaptations to Functional Changes from Without 172
True Functional Adaptation 176
Theoretical Conclusions 179

2. PHYSIOLOGICAL ADAPTATION 184

Specific Adaptedness *not* “Adaptation” 186
Primary and Secondary Adaptations in Physiology 188
On Certain Pre-requisites of Adaptations in General 189
On Certain Groups of Primary Physiological Adaptations 190

General Remarks on Irritability 190
The Regulation of Heat Production 193
Primary Regulations in the Transport of Materials and
Certain Phenomena of Osmotic Pressure 194
Chromatic Regulations in Algae 197
Metabolic Regulations 198

Immunity the only Type of a Secondary Physiological
Adaptation 204
No General Positive Result from this Chapter 209
A few Remarks on the Limits of Regulability 212

*D.* INHERITANCE. SECOND PROOF OF THE AUTONOMY OF LIFE--

The Material Continuity in Inheritance 214
On Certain Theories which Seek to Compare Inheritance to Memory 216
The Complex-Equipotential System and its Rôle in Inheritance 219
The Second Proof of Life-Autonomy. Entelechy at the Bottom
of Inheritance 224
The Significance of the Material Continuity in Inheritance 227
The Experimental Facts about Inheritance 228
The Rôle of the Nucleus in Inheritance 233
Variation and Mutation 237

*CONCLUSIONS FROM THE FIRST MAIN PART OF THESE LECTURES* 240

PART II.--SYSTEMATICS AND HISTORY

*A.* THE PRINCIPLES OF SYSTEMATICS--

Rational Systematics 243
Biological Systematics 246

*B.* THE THEORY OF DESCENT--

1. GENERALITIES 250

The Covert Presumption of all Theories of Descent 253
The Small Value of Pure Phylogeny 255
History and Systematics 257

2. THE PRINCIPLES OF DARWINISM 260

Natural Selection 261
Fluctuating Variation the Alleged Cause of Organic Diversity 264
Darwinism Fails all along the Line 269

3. THE PRINCIPLES OF LAMARCKISM 271

Adaptation as the Starting-Point 272
The Active Storing of Contingent Variations as a
Hypothetic Principle 273
Criticism of the “Inheritance of Acquired Characters”
assumed by Lamarckism 275
Other Principles Wanted 281
Criticism of the Hypothesis of Storing and Handing Down
Contingent Variations 282

4. THE REAL RESULTS AND THE UNSOLVED PROBLEMS OF TRANSFORMISM 290

5. THE LOGICAL VALUE OF THE ORGANIC FORM ACCORDING TO THE
DIFFERENT TRANSFORMISTIC THEORIES 293

The Organic Form and Entelechy 294

*C.* THE LOGIC OF HISTORY 297

1. THE POSSIBLE ASPECTS OF HISTORY 299

2. PHYLOGENETIC POSSIBILITIES 304

3. THE HISTORY OF MANKIND 306

Cumulations in Human History 308
Human History not an “Evolution” 311
The Problem of the “Single” as such 315

*CONCLUSIONS ABOUT SYSTEMATICS AND HISTORY IN GENERAL* 322

THE PROGRAMME

ON LORD GIFFORD’S CONCEPTION OF “SCIENCE”

This is the first time that a biologist has occupied this place; the
first time that a biologist is to try to carry out the intentions of the
noble and high-minded man to whom this lectureship owes its foundation.

On such an occasion it seems to be not undesirable to inquire what Lord
Gifford’s own opinions about natural science may have been, what place
in the whole scheme of human knowledge he may have attributed to those
branches of it which have become almost the centre of men’s intellectual
interest.

And, indeed, on studying Lord Gifford’s bequest with the object of
finding in it some reference to the natural sciences, one easily notes
that he has assigned to them a very high place compared with the other
sciences, at least in one respect: with regard to their methods.

There is a highly interesting passage in his will which leaves no doubt
about our question. After having formally declared the foundation of
this lectureship “for Promoting, Advancing, Teaching and Diffusing
the study of Natural Theology in the widest sense of that term,” and
after having arranged about the special features of the lectures, he
continues: “I wish the lecturers to treat their subject as a strictly
natural science, the greatest of all possible sciences, indeed, in one
sense, the only science, that of Infinite Being.... I wish it considered
just as astronomy or chemistry is.”

Of course, it is not possible to understand these words of Lord
Gifford’s will in a quite literal sense. If, provisionally, we call
“natural theology” the ultimate conclusions which may be drawn from a
study of nature in connection with all other results of human sciences,
there cannot be any doubt that these conclusions will be of a rather
different character from the results obtained in, say, the special field
of scientific chemistry. But, nevertheless, there are, I think, two
points of contact between the wider and the narrower field of knowledge,
and both of them relate to method. Lord Gifford’s own phrase, “Infinite
Being,” shows us one of these meeting-points. In opposition to history
of any form, natural sciences aim at discovering such truths as are
independent of special time and of special space, such truths as are
“ideas” in the sense of Plato; and such eternal results, indeed, always
stand in close relation to the ultimate results of human knowledge
in general. But besides that there is still another feature which
may be common both to “natural theology” and to the special natural
sciences, and which is most fully developed in the latter: freedom from
prepossessions. This, at least, is an ideal of all natural sciences;
I may say it is *the* ideal of them. That it was this feature which
Lord Gifford had in view in his comparison becomes clear when we read
in his will that the lectures on natural theology are to be delivered
“without reference to or reliance upon any supposed special exceptional
or so-called miraculous revelation.”

So we might say that both in their logical and their moral methods,
natural sciences are to be the prototype of “Natural Theology” in Lord
Gifford’s sense.

NATURAL SCIENCES AND “NATURAL THEOLOGY”

But now let us study in a more systematic manner the possible relations
of the natural sciences to natural theology as a science.

How is it possible for a natural scientist to contribute to the science
of the highest and ultimate subject of human knowledge?

Almost all natural sciences have a sort of naïveté in their own spheres;
they all stand on the ground of what has been called a naïve realism,
as long as they are, so to say, at home. That in no way prejudices
their own progress, but it seems to stand in the way of establishing
contact with any higher form of human knowledge than themselves.
One may be a first-rate organic chemist even when looking upon the
atoms as small billiard balls, and one may make brilliant discoveries
about the behaviour of animals even when regarding them in the most
anthropomorphic manner--granted that one is a good observer; but it
can hardly be admitted that our chemist would do much to advance the
theory of matter, or our biologist to solve the problem of the relations
between body and mind.

It is only by the aid of philosophy, or I would rather say by keeping
in constant touch with it, that natural sciences are able to acquire
any significance for what might be called *the* science of nature in the
most simple form. Unhappily the term “natural philosophy” is restricted
in English to theoretical physics. This is not without a high degree of
justification, for theoretical physics has indeed lost its naïveté and
become a philosophy of nature; but it nevertheless is very unfortunate
that this use of the term “natural philosophy” is established in
this country, as we now have no proper general term descriptive of a
natural science that is in permanent relation to philosophy, a natural
science which does not use a single concept without justifying it
epistemologically, *i.e.* what in German, for instance, would simply be
called “Naturphilosophie.”

Let us call it philosophy of nature; then we may say that only by
becoming a true philosophy of nature are natural sciences of all sorts
able to contribute to the highest questions which man’s spirit of
inquiry can suggest.

These highest questions themselves are the outcome of the combination
of the highest results of all branches of philosophy, just as our
philosophy of nature originated in the discussion of the results of
all the separate natural sciences. Are those highest questions not
only to be asked, are they to be also solved? To be solved in a way
which does not exceed the limits of philosophy as the domain of actual
understanding?

The beginning of a long series of studies is not the right place to
decide this important question; and so, for the present certainly,
“natural theology” must remain a problem. In other words: it must
remain an open question at the beginning of our studies, whether after
all there can be any final general answer, free from contradictions,
applicable to the totality of questions asked by all the branches of
philosophy.

But let us not be disturbed by this problematic entrance to our studies.
Let us follow biology on its own path; let us study its transition from
a “naïve” science to a real branch of the philosophy of nature. In this
way we perhaps shall be able to understand what its part may be in
solving what can be solved.

That is to be our subject.

OUR PHILOSOPHICAL BASIS

We call *nature* what is given to us in space.

Of course we are not obliged in these lectures to discuss the
psychological and epistemological problems of space with its three
dimensions, nor are we obliged to develop a general theory of reality
and its different aspects. A few epistemological points will be
considered later at proper times, and always in connection with results
of theoretical biology.

At present it must suffice to say that our general philosophical point
of view will be idealistic, in the critical meaning of the word. The
universe, and within the universe nature, in the sense just defined,
is my phenomenon. That is what I know. I know nothing more, either
positively or negatively; that is to say, I do not know that the world
is *only my* phenomenon, but, on the other hand, I know nothing about
its “absolute reality.” And more, I am not even able to describe in
intelligible words what “absolute reality” might mean. I am fully
entitled to state: the universe *is* as truly as I am--though in
a somewhat different sense of “being”--and I *am* as truly as the
universe is; but I am not entitled to state anything beyond these
two corresponding phrases. You know that, in the history of European
philosophy at least, Bishop Berkeley was the first clearly to outline
the field of idealism.

But my phenomenon--the world, especially nature--consists of elements
of two different kinds: some of them are merely passive, some of them
contain a peculiar sort of activity in themselves. The first are
generally called sensations, but perhaps would be better called elements
or presentations; the others are forms of construction, and, indeed,
there is an active element embraced in them in this sense, that they
allow, by their free combination, the discovery of principles which
are not to be denied, which must be affirmed, whenever their meaning
is understood. You know that I am speaking here of what are generally
called categories and synthetic judgments *a priori*, and that it was
Kant who, on the foundations laid by Locke, Hume, and Leibnitz, first
gave the outlines of what may be called the real system of critical
philosophy. Indeed, our method will be to a great extent Kantian, though
with certain exceptions; it is to be strictly idealistic, and will not
in the Kantian way operate with things in themselves; and it regards
the so-called “synthetic judgment *a priori*” and the problem of the
relation between categorical principles and experience in a somewhat
different manner. We think it best to define the much disputed concept
“*a priori*” as “independent of the *amount* of experience”; that is
to say, all categories and categorical principles are brought to my
consciousness by that fundamental event which is called experience, and
therefore are not independent of it, but they are not inferences from
experience, as are so-called empirical laws. We almost might say that we
only have to be reminded of those principles by experience, and, indeed,
we should not, I think, go very far wrong in saying that the Socratic
doctrine, that all knowledge is recollection, holds good as far as
categories and categorical principles are in question.

But enough at present about our general philosophy.

As to the philosophy of nature, there can be no doubt that, on the basis
of principles like those we have shortly sketched, its ultimate aim must
be to co-ordinate everything in nature with terms and principles of the
categorical style. The philosophy of nature thus becomes a system; a
system of which the general type is afforded by the innate constructive
power of the Ego. In this sense the Kantian dictum remains true, that
the Ego prescribes its own laws to nature, though, of course, “nature,”
that is, what is given in space, must be such as to permit that sort of
“prescription.”

One often hears that all sciences, including the science of sciences,
philosophy, have to find out what is true. What, then, may be called
“true” by an idealistic philosopher, for whom the old realistic formula
of the conformity between knowledge and the object cannot have any
meaning? Besides its ordinary application to simple facts or to simple
judgments, where the word truth only means absence of illusion or no
false statement, truth can be claimed for a philosophical doctrine or
for a system of such doctrines only in the sense that there are no
contradictions amongst the parts of the doctrine or of the system
themselves, and that there are no features in them which impel our
categorical Ego to further analysis.

Those of you who attended Professor Ward’s lectures on “Naturalism and
Agnosticism,” or who have read his excellent book on that subject, will
know what the aims of a theory of matter are. You will also be aware
that, at present, there does not exist any theory of matter which can
claim to be “true”; there are contradictions in every theory of matter,
and, moreover, there are always some points where we are obliged to ask
for further information and receive no answer. Experience here has not
yet aroused all the categorical functions which are needed in order to
form one unity out of what seem to be incompatibilities at the present
day. Why is that? Maybe because experience is not yet complete in this
field, but maybe also because the whole subject is so complicated
that it takes much time to attach categorical functions to what is
experienced.

But it is not our object here to deal either with epistemology proper
or with ontology: a full analysis of biological facts is our problem.
Why, then, all these introductions? why all these philosophical sketches
in fields of knowledge which have quite another relation to philosophy
than biology has? Biology, I hear some one say, is simply and solely
an empirical science; in some sense it is nothing but applied physics
and chemistry, perhaps applied mechanics. There are no fundamental
principles in biology which could bring it in any close contact with
philosophy. Even the one and only principle which might seem to be
an innate principle of our experience about life, the principle of
evolution, is only a combination of more simple factors of the physical
and chemical type.

It will be my essential endeavour to convince you, in the course of
these lectures, that such an aspect of the science of biology is wrong;
that biology is an elemental natural science in the true sense of the
word.

But if biology is an elemental science, then, and only then, it stands
in close relations to epistemology and ontology--in the same relations
to them, indeed, as every natural science does which deals with true
elements of nature, and which is willing to abandon naïve realism and
contribute its share to the whole of human knowledge.

And, therefore, a philosophical sketch is not out of place at the
beginning of lectures on the Philosophy of the Organism. We may be
forced, we, indeed, shall be forced, to remain for some time on the
ground of realistic empiricism, for biology has to deal with very
complicated experiences; but there will be a moment in our progress when
we shall enter the realm of the elemental ontological concepts, and
in that very moment our study of life will have become a part of real
philosophy. It was not without good reasons, therefore, that I shortly
sketched, as a sort of introduction to my lectures, the general point of
view which we shall take with regard to philosophical questions, and to
questions of the philosophy of nature in particular.

ON CERTAIN CHARACTERISTICS OF BIOLOGY AS A SCIENCE

Biology is the science of life. Practically, all of you know what a
living being is, and therefore it is not necessary to formulate a
definition of life, which, at the beginning of our studies, would be
either provisional and incomplete, or else dogmatic. In some respects,
indeed, a definition should rather be the end of a science than its
opening.

We shall study the phenomena of living organisms analytically, by the
aid of experiment; our principal object will be to find out laws in
these phenomena; such laws will then be further analysed, and precisely
at that point we shall leave the realm of natural science proper.

Our science is the highest of all natural sciences, for it embraces as
its final object the actions of man, at least in so far as actions also
are phenomena observable on living bodies.

But biology is also the most difficult of all natural sciences, not
only from the complexity of the phenomena, which it studies, but in
particular for another reason which is seldom properly emphasised, and
therefore will well repay us for a few words devoted to it.

Except so far as the “elements” of chemistry come into account, the
experimenter in the inorganic fields of nature is not hampered by the
specificity of composite objects: he makes all the combinations he
wants. He is always able to have at his disposal red rays of a desired
wave length when and where he wants, or to have, at a given time and
place, the precise amount of any organic compound which he wishes to
examine. And he forces electricity and electromagnetism to obey his
will, at least with regard to space, time, and intensity of their
appearance.

The biologist is not able to “make” life, as the physicist has made red
rays or electromagnetism, or as the chemist has made a certain compound
of carbon. The biologist is almost always in that strange plight in
which the physicist would be if he always had to go to volcanoes in
order to study the conductivity of heat, or if he had to wait for
thunderstorms in order to study electricity. The biologist is dependent
on the specificity of living objects as they occur in nature.

A few instances may show you what great inconveniences may hence arise
to impede practical biological research. We later on shall have to deal
with experiments on very young embryos: parts of the germ will have
to be destroyed in order to study what will happen with the rest. Now
almost all germs are surrounded by a membrane; this membrane has to be
detached before any operation is possible. But what are we to do if it
is not possible to remove the membrane without killing the embryo? Or
what if, as for instance in many marine animals, the membrane may be
removed but the germs are killed by contact with sea-water? In both
cases no experiments at all will be possible on a sort of germ which
otherwise, for some special circumstances of its organisation, might
have given results of importance. These results become impossible for
only a practical, for a very secondary reason; but enough: they are
impossible, and they might have thrown light on problems which now
must remain problems. Quite the same thing may occur in experiments
on physiology proper or functional physiology: one kind of animals
survives the operation, the other kind does not, and therefore, for
merely extrinsic reasons, the investigations have to be restricted to
the first, though the second might have given more important results.
And thus the biological experimenter always finds himself in a sort of
dependence on his subjects, which can hardly be called pleasant. To a
great extent the comparatively slow advance of biological sciences is
due to this very fact: the unalterable specific nature of biological
material.

But there is still another feature of biology dependent on the same
fact. If a science is tied down to specific objects in every path it
takes, it first, of course, has to know all about those objects, and
that requires nothing else but plain description. We now understand why
pure description, in the most simple sense of the word, takes up such an
enormous part of every text-book of biological science. It is not only
morphology, the science of form, that is most actively concerned with
description; physiology also, in its present state, is pure description
of what the functions of the different parts of the body of animals and
plants actually *are*, at least for about nine-tenths of its range. It
seems to me important to press this point very emphatically, since we
often hear that physiology is from the very beginning a much higher sort
of knowledge than morphology, inasmuch as it is rational. That is not at
all true of the beginning of physiology: what the functions of the liver
or of the root are has simply to be described just as the organisation
of the brain or of the leaf, and it makes no difference logically that
one species of description has to use the experimental method, while the
other has not. The experiment which only discovers what happens here or
what happens there, possesses no kind of logical superiority over pure
description at all.

But there will be another occasion in our lectures to deal more fully
with the logic of experiment and with the differences of descriptive
knowledge and real rational science.

THE THREE DIFFERENT TYPES OF KNOWLEDGE ABOUT NATURE

Natural sciences cannot originate before the given phenomena of nature
have been investigated in at least a superficial and provisional manner,
by and for the practical needs of man. But as soon as true science
begins in any limited field, dealing, let us say, with animals or with
minerals, or with the properties of bodies, it at once finds itself
confronted by two very different kinds of problems, both of them--like
all “problems”--created in the last resort by the logical organisation
of the human mind, or, to speak still more correctly, of the Ego.

In any branch of knowledge which practical necessities have separated
from others, and which science now tries to study methodically, there
occur general sequences in phenomena, general orders of events. This
uniformity is revealed only gradually, but as soon as it has shown
itself, even in the least degree, the investigator seizes upon it. He
now devotes himself chiefly, or even exclusively, to the generalities in
the sequences of all changes. He is convinced that there must be a sort
of most general and at the same time of most universal connection about
all occurrences. This most universal connection has to be found out; at
least it will be the ideal that always will accompany the inquiring mind
during its researches. The “law of nature” is the ideal I am speaking
about, an ideal which is nothing less than one of the postulates of the
possibility of science at all.

Using for our purposes a word which has been already introduced into
terminology by the philosopher Windelband, though in a somewhat
different sense, we shall call that part of every branch of natural
sciences which regards the establishment of a law of nature as its
ideal, “nomothetic,” *i.e.* “law-giving.”

But while every natural science has its nomothetic side, it also has
another half of a very different kind. This second half of every natural
science does not care for the same general, the same universal, which
is shown to us in every event in a different and specified kind: it
is diversity, it is specification, that constitutes the subject of
its interest. Its aim is to find a sufficient reason for the types of
diversities, for the types of specifications. So in chemistry there
has been found a systematic order in the long series of the compounds
and of the elements; crystallography also has its different systems of
crystals, and so on.

We have already employed the word by which we shall designate this
second half of every natural science: it is the “systematic” side of
science.

Nomothetic work on the one side and systematics on the other do, in
fact, appear in every natural science, and besides them there are no
other main parts. But “science” as a whole stands apart from another
aspect of reality which is called “history.” History deals with
particulars, with particular events at such and such a place, whilst
science always abstracts from the particular, even in its systematic
half.[1]

[1] Windelband (*Geschichte und Naturwissenschaft*, 3 Auflage, 1904)
gives the name “nomothetic” to the whole of our “science” and calls the
method of history “idiographic.” We thought it better to establish three
fundamental types of all possible branches of knowledge.

GENERAL PLAN OF THESE LECTURES

Turning now to a sort of short outline of what is to be discussed
in the whole of our future lectures, this summer and next, it seems
clear, without further analysis, that biology as a science has its
nomothetic and its systematic part also; respiration and assimilation,
for instance, have proved to be types of natural laws among living
phenomena, and that there is a “system” of animals and plants is too
commonly known to require further explanation here. Therefore we might
study first biological laws, and after that biological systematics, and
in the third place perhaps biological history. But that would hardly
correspond to the philosophical aims of our lectures: our chief object
is not biology as a regular science, as treated in text-books and in
ordinary university lectures; our chief object is the Philosophy of the
Organism, as aided and supported by scientific biology. Therefore a
general acquaintance with biology must be assumed in these lectures, and
the biological materials must be arranged according to their bearing on
further, that is on philosophical, analysis.

That will be done, not, of course, to the extent of my regarding every
one of my audience as a competent biologist; on the contrary, I shall
explain most fully all points of biology proper, and even of the most
simple and descriptive kind of biology, which serve as bases for
philosophical analysis. But I shall do so only if they indeed do serve
as such bases. All our biology will be not for its own sake, but for the
sake of philosophy.

Whilst regarding the whole of the biological material with such aims,
it seems to me best to arrange the properly scientific material which
is to be the basis of my discussions, not along the lines which biology
as an independent science would select,[2] but to start from the three
different kinds of fundamental phenomena which living bodies offer to
investigation, and to attach all systematics exclusively to one of them.
For there will not be very much for philosophy to learn from biological
systematics at present.

[2] See J. Arth. Thomson, *The Science of Life*, London, 1899.

Life is unknown to us except in association with bodies: we only know
living bodies and call them organisms. It is the final object of all
biology to tell us what it ultimately means to say that a body is
“living,” and in what sorts of relation body and life stand one to the
other.

But at present it is enough to understand the terms “body” and “living”
in the ordinary and popular sense.

Regarding living bodies in this unpretentious manner, and recollecting
what the principal characters are of all bodies we know as living ones,
we easily find that there are three features which are never wanting
wherever life in bodies occurs. All living bodies are specific as to
form--they “have” a specific form, as we are accustomed to say. All
living bodies also exhibit metabolism; that is to say, they stand in a
relation of interchange of materials with the surrounding medium, they
take in and give out materials, but their form can remain unchanged
during these processes. And, in the last place, we can say that all
living bodies move; though this faculty is more commonly known among
animals only, even elementary science teaches the student that it also
belongs to plants.

Therefore we may ask for “laws of nature” in biology about form, about
metabolism, and about movements. In fact, it is according to this scheme
that we shall arrange the materials of the biological part of our
lectures, though, as we cannot regard the three divisions as equally
important in their bearing on our ultimate purposes, we shall not treat
them quite on equal terms. It will appear that, at least in the present
state of science, the problems of organic form and of organic movement
have come into much closer relation to philosophical analysis than have
most of the empirical data on metabolism.

It is *form* particularly which can be said to occupy the very centre
of biological interest; at least it furnishes the foundation of all
biology. Therefore we shall begin our scientific studies with a full and
thorough analysis of form. The science of living forms, later on, will
afford us a key to study metabolism proper with the greatest advantage
for our philosophical aims, and therefore the physiology of what is
usually called the vegetative functions will be to us a sort of appendix
to our chapters on form; only the theory of a problematic “living
substance” and of assimilation in the most general meaning of the word
will be reserved for the philosophical part; for very good reasons,
as I hope to show. But our chapters on the living forms will have yet
another appendix besides the survey of the physiology of metabolism.
Biological systematics almost wholly rests on form, on “morphology”; and
what hitherto has been done on the metabolical side of their problems,
consists of a few fragments, which are far from being an equivalent to
the morphological system; though, of course it must be granted that,
logically, systematics, in our general meaning of the word, as the sum
of problems about the typically different and the specific, may be
studied on the basis of each one of the principal characteristics of
living bodies, not only on that of their forms. Therefore, systematics
is to be the second appendix to the chief part of our studies in
morphology, and systematics, in its turn, will later on lead us to
a short sketch of the historical side of biology, to the theory of
evolution in its different forms, and to the logic of history in general.

So far will our programme be carried out during this summer. Next year
the theory of movements will conclude our merely scientific analysis,
and the remaining part of the course next summer will be devoted to the
philosophy of living nature. I hope that nobody will be able to accuse
our philosophy of resting on unsound foundations. But those of you, on
the other hand, who would be apt to regard our scientific chapters as a
little too long compared with their philosophical results, may be asked
to consider that a small clock-tower of a village church is generally
less pretentious but more durable than the campanile of San Marco has
been.

Indeed, these lectures will afford more “facts” to my hearers, than
Gifford Lectures probably have done, as a rule. But how could that
be otherwise on the part of a naturalist? Scientific facts are the
material that the philosophy of nature has to work with, but these
facts, unfortunately, are not as commonly known as historical facts,
for instance, generally are; and they must be known, in order that a
philosophy of the organism may be of any value at all, that it may be
more than a mere entertainment.

Goethe once said, that even in so-called facts there is more “theory”
than is usually granted; he apparently was thinking of what might be
called the ultimate or the typical facts in science. It is with such
typical or ultimate facts, of course, that we must become acquainted if
our future philosophy is to be of profit to us.

Certainly, there would be nothing to prevent us from arranging our
materials in a manner exactly the reverse of that which we shall adopt;
we could begin with a general principle about the organic, and could
try to deduce all its special features from that principle, and such a
way perhaps would seem to be the more fascinating method of argument.
But though logical it would not be psychological, and therefore would
be rather unnatural. And thus our *most* general principle about the
organic will not come on the scene before the eighteenth of these twenty
lectures, although it is not a mere inference or deduction from the
former lectures: it will be a culmination of the whole, and we shall
appreciate its value the better the more we know what that whole really
is.

GENERAL CHARACTER OF THE ORGANIC FORM

Our programme of this year, it was said, is to be devoted wholly
to organic forms, though one of its appendixes, dealing with some
characteristics of the physiology of metabolism, will lead us on to a
few other phenomena. What then are the essentials of a living form, as
commonly understood even without a special study of biology?

Living bodies are not simple geometrical forms, not, like crystals,
merely a typical arrangement of surfaces in space, to be reduced
theoretically, perhaps, to an arrangement of molecules. Living bodies
are typically combined forms; that is to say, they consist of simpler
parts of different characters, which have a special arrangement with
regard to one another; these parts have a typical form of their own and
may again be combinations of more simple different parts. But besides
that, living bodies have not always the same typically combined form
during the whole of their life: they become more complicated as they
grow older; they all begin from one starting point, which has little
form at all, viz., the egg. So the living form may be called a “genetic
form,” or a form considered as a process, and therefore *morphogenesis*
is the proper and adequate term for the science which deals with the
laws of organic forms in general; or, if you prefer not to use the
same word both for a science and for the subjects of that science, the
*physiology of morphogenesis*.

Now there are different branches of the physiology of morphogenesis or
physiology of form. We may study, and indeed we at first shall study,
what are the laws of the morphogenetic processes leading from the egg
to the adult: that may be properly called physiology of development.
But living forms are not only able to originate in one unchangeable
way: they may restore themselves, if disturbed, and thus we get the
physiology of restoration or restitution as a second branch of the
science of morphogenesis. We shall draw very important data, some of the
foundations indeed of our philosophical discussions, from the study of
such restitutions. Besides that, it is to them that our survey of the
problems of the physiology of metabolism is to be appended.

Living forms not only originate from the egg and are able to restore
themselves, they also may give origin to other forms, guaranteeing in
this way the continuity of life. The physiology of heredity therefore
appears as the counterpart to those branches of the physiology of form
which deal with individual form and its restitutions. And our discussion
on heredity may be followed by our second appendix to this chief section
on form, an appendix regarding the outlines of systematics, evolution
and history.

Theoretical considerations on biology generally start, or at least,
used to start, from the evolution theory, discussing all other problems
of the physiology of form by the way only, as things of secondary
importance. You see from our programme, that we shall go just the
opposite way: evolution will come last of all, and will be treated
shortly; but the morphogenesis of the individual will be treated very
fully, and very carefully indeed.

Why then this deviation from what is the common practice? Because we do
not know very much about evolution at all, because in this field we are
just at the very beginning of what deserves the name of exact knowledge.
But concerning individual morphogenesis we really know, even at present,
if not very much, at least something, and that we know in a fairly exact
form, aided by the results of experiments.

And it will not be without its reward, if we restrict our aims in such a
manner, if we prefer to deal more fully with a series of problems, which
may seem at the first glance to be of less interest than others. After a
few lectures we shall find already that we may decide one very important
question about life merely by an analysis of individual form production,
and without any regard to problematic and doubtful parts of biology:
that we may decide the question, whether “life” is only a combination
of chemical and physical events, or whether it has its elemental laws,
laws of its own.

But to prepare the road that is to lead to such results we first have
to restrict our aims once more, and therefore the next lecture of this
course, which eventually is to touch almost every concept of philosophy
proper, will begin with the pure description of the individual
development of the common sea-urchin.

SECTION A

THE CHIEF RESULTS OF ANALYTICAL BIOLOGY

PART I

THE INDIVIDUAL ORGANISM WITH REGARD TO FORM AND METABOLISM

*A.* ELEMENTARY MORPHOGENESIS

EVOLUTIO AND EPIGENESIS IN THE OLD SENSE

The organism is a specific body, built up by a typical combination
of specific and different parts. It is implied in the words of this
definition, that the organism is different, not only from crystals, as
was mentioned in the last lecture, but also from all combinations of
crystals, such as those called dendrites and others, which consist of a
typical arrangement of identical units, the nature of their combination
depending on the forces of every single one of their parts. For this
reason dendrites, in spite of the typical features in their combination,
must be called aggregates; but the organism is not an aggregate even
from the most superficial point of view.

We have said before, what must have been familiar to you already, that
the organism is not always the same in its individual life, that it
has its development, leading from simpler to more complicated forms of
combination of parts; there is a “production of visible manifoldness”
carried out during development, to describe the chief character of that
process in the words of Wilhelm Roux. We leave it an open question in
our present merely descriptive analysis, whether there was already a
“manifoldness,” in an invisible state, before development, or whether
the phrase “production of manifoldness” is to be understood in an
absolute sense.

It has not always been granted in the history of biology, and of
embryology especially, that production of visible manifoldness is the
chief feature of what is called an organism’s embryology or ontogeny:
the eighteenth century is full of determined scientific battles over the
question. One school, with Albert von Haller and Bonnet as its leading
men, maintained the view that there was no production of different parts
at all in development, this process being a mere “evolutio,” that is,
a growth of parts already existing from the beginning, yes, from the
very beginning of life; whilst the other school, with C. F. Wolff and
Blumenbach at its head, supported the opposite doctrine of so-called
“epigenesis,” which has been proved to be the right one.

To some extent these differences of opinion were only the outcome of the
rather imperfect state of the optical instruments of that period. But
there were also deeper reasons beyond mere difficulties of description;
there were theoretical convictions underlying them. It is *impossible*,
said the one party, that there is any real production of new parts;
there *must* be such a production, said the other.

We ourselves shall have to deal with these questions of the theory of
organic development; but at present our object is narrower, and merely
descriptive. It certainly is of great importance to understand most
clearly that there actually *is* a “production of visible manifoldness”
during ontogenesis in the descriptive sense; the knowledge of the fact
of this process must be the very foundation of all studies on the theory
of development in any case, and therefore we shall devote this whole
lecture to studies in merely descriptive embryology.

But descriptive embryology, even if it is to serve merely as an
instance of the universality of the fact of epigenesis, can only be
studied successfully with reference to a concrete case. We select the
development of the common sea-urchin (*Echinus microtuberculatus*) as
such a case, and we are the more entitled to select this organism rather
than another, because most of the analytical experimental work, carried
out in the interests of a real theory of development, has been done
on the germs of this animal. Therefore, to know at least the outlines
of the individual embryology of the Echinus may indeed be called the
*conditio sine qua non* for a real understanding of what is to follow.

THE CELL[3]

[3] E. B. Wilson, *The Cell in Development and Inheritance*, New York,
Macmillan, 1896.

You are aware that all organisms consist of organs and that each of
their organs has a different function: the brain, the liver, the eyes,
the hands are types of organs in animals, as are the leaves and the
pistils in plants.

You are also aware that, except in the lowest organisms, the so-called
Protista, all organs are built up of cells. That is a simple fact of
observation, and I therefore cannot agree with the common habit of
giving to this plain fact the title of cell-“theory.” There is nothing
theoretical in it; and, on the other hand, all attempts to conceive
the organism as a mere aggregate of cells have proved to be wrong. It
is *the whole* that uses the cells, as we shall see later on, or that
may not use them: thus there is nothing like a “cell-theory,” even in a
deeper meaning of the word.

The cell may have the most different forms: take a cell of the skin, of
a muscle, of a gland, of the wood in plants as typical examples. But in
every case two parts may be distinguished in a cell: an outside part,
the protoplasm, and an inside part, the nucleus, to leave out of special
account several others, which, by the way, may only be protoplasmatic
modifications.

Protoplasm is a mere name for what is not the nucleus; in any case it is
not a homogeneous chemical compound; it consists of many such compounds
and has a sort of architecture; all organic functions are based upon
its metabolism. The nucleus has a very typical structure, which stands
in a close relation to its behaviour during the most characteristic
morphological period of the cell: during its division. Let us devote a
few words to a consideration of this division and the part the nucleus
plays in it; it will directly bear on future theoretical considerations
about development.

There is a certain substance in every nucleus of a cell which stains
most markedly, whenever cells are treated with pigments: the name
of “chromatin” has been given to it. The chromatin always gives the
reaction of an acid, while protoplasm is basic; besides that it seems to
be a centre of oxidation. Now, when a division of a cell is to occur,
the chromatin, which had been diffusely distributed before, in the form
of small grains, arranges itself into a long and very much twisted
thread. This thread breaks, as it were by sections, into almost equal
parts, typical in number for each species, and each of these parts is
split at full length. A certain number of pairs of small threads, the
so-called “chromosomes,” are the ultimate result of this process, which
intentionally has been described a little schematically, the breaking
and the splitting in fact going on simultaneously or occasionally even
in reverse order. While what we have described is performing in the
nucleus, there have happened some typical modifications in protoplasm,
and then, by an interaction of protoplasmatic and nuclear factors, the
first step in the actual division of the cell begins. Of each pair of
the small threads of chromatin one constituent is moved to one side of
the cell, one to the other; two daughter-nuclei are formed in this way;
the protoplasm itself at the same time forms a circular furrow between
them; the furrow gets deeper and deeper; at last it cuts the cell in
two, and the division of the cell is accomplished.

Not only is the growth of the already typically formed organism carried
out by a series of cell-divisions, but also development proper in our
sense, as a “production of visible manifoldness,” is realised to a great
extent by the aid of such divisions, which therefore may indeed be said
to be of very fundamental importance (Fig. 1).

[Illustration: Fig. 1.--Diagram of Cell-Division (*after* Boveri).

*a.* Resting cell; the chromatin distributed in the form of small
granules inside the nucleus. Outside the nucleus is the “centrosome,”
not mentioned in the text.

*b.* Beginning of division; the chromatin arranged in the form of a long
thread. Centrosome divided in two.

*c.* The thread of chromatin cut into four parts, the “chromosomes.”

*d.* The four parts of the chromatin arranged symmetrically between the
centrosomes and the star-like “spheres.”

*e.* Each of the chromosomes split at full length.

*f.* Beginning of division of protoplasm; the two parts of each
chromosome separated.

*g.* End of cell-division.]

Each cell-division which promotes growth is followed by the
enlargement of the two daughter-cells which result from it; these two
daughter-elements attain the exact size of the mother-cell before
division, and as soon as this size is reached a new division begins:
so the growth of the whole is in the main the result of the growth of
the elements. Cell-divisions during real organ-formation may behave
differently, as will be described at a proper occasion.

THE EGG: ITS MATURATION AND FERTILISATION

We know that all the organs of an animal or plant consist of cells, and
we know what acts a cell can perform. Now there is one very important
organ in all living beings, which is devoted to reproduction. This
organ, the so-called ovary in animals, is also built up of cells,
and its single cells are called the eggs; the eggs originated by
cell-division, and cell-division is to lead from them to the new adult.

But, with a very few exceptions, the egg in the ovary is not able to
accomplish its functions, unless certain typical events have occurred,
some of which are of a merely preparatory kind, whilst the others are
the actual stimulus for development.

The preparatory ones are generally known under the name of “maturation.”
The egg must be “mature,” in order that it may begin development, or
even that it may be stimulated to it. Maturation consists of a rather
complicated series of phenomena: later on we shall have occasion to
mention, at least shortly, what happens in the protoplasm during its
course; as to the nuclear changes during maturation it may be enough
for our purposes to say, that there occur certain processes among the
chromosomes, which lead to an extension of half of them in the form
of two very small cells, the “directive cells” or “directive or polar
bodies,” as they have been somewhat cautiously called.

The ripe or mature egg is capable of being fertilised.

Before turning to this important fact, which, by the way, will bring us
to our specially chosen type, the Echinus, a few words may be devoted to
the phenomenon of “parthenogenesis,” that is to say, the possibility
of development without fertilisation, since owing to the brilliant
discoveries of the American physiologist, Jacques Loeb, this topic forms
one of the centres of biological interest at present. It has long been
known that the eggs of certain bees, lice, crayfishes, and other animals
and also plants, are capable of development without fertilisation at
all. Now Richard Hertwig and T. H. Morgan already had shown, that at
least nuclear division may occur in the eggs of other forms--in the egg
of the sea-urchin for instance--when these eggs are exposed to some
chemical injuries. But Loeb[4] succeeded in obtaining a full development
by treating the eggs of echinoderms with chloride of magnesium; thus
artificial parthenogenesis had been discovered. Later researches have
shown that artificial parthenogenesis may occur in all classes of the
animal kingdom and may be provoked by all sorts of chemical or physical
means. We do not know at present in what the proper stimulus consists
that must be supposed here to take the place of fertilisation; it seems,
of course, highly probable that it is always the same in the last
resort.[5]

[4] *Amer. Journ. Physiol.* vols. iii. and iv. 1900.

[5] According to Delage (*Arch. Zool. exp.*, 3 sér. 10, 1902), it is
indifferent for the realisation of artificial parthenogenesis, whether
but one, or both, or neither of the “polar bodies” has been formed. But
the egg must be in the first stages of maturation to the extent that the
“nuclear membrane” must be already dissolved.

But enough about processes, which at present are of a highly scientific,
but hardly of any philosophic interest.

By fertilisation proper we understand the joining of the male element,
the spermatozoon or the spermia, with the female element, the egg. Like
the egg, the spermatozoon is but a cell, though the two differ very much
from one another in the relation between their protoplasm and nucleus:
in all eggs it is the protoplasm which is comparatively very large, if
held together with somatic cells, in the spermatozoon it is the nucleus.
A large amount of reserve material, destined for the growth of the
future being, is the chief cause of the size of the egg-protoplasm. The
egg is quite or almost devoid of the faculty of movement, while on the
contrary, movement is the most typical feature of the spermia. Its whole
organisation is adapted to movement in the most characteristic manner:
indeed, most spermatozoa resemble a swimming infusorium, of the type
of Flagellata, a so-called head and a moving tail are their two chief
constituents; the head is formed almost entirely of nuclear substance.

It seems that in most cases the spermatozoa swim around at random and
that their union with the eggs is assured only by their enormous number;
only in a few cases in plants have there been discovered special stimuli
of a chemical nature, which attract the spermia to the egg.

But we cannot enter here more fully into the physiology of
fertilisation, and shall only remark that its real significance is by no
means clear.[6]

[6] The older theories, attributing to fertilisation (or to
“conjugation,” *i.e.* its equivalent in Protozoa), some sort of
“renovation” or “rejuvenescence” of the race, have been almost
completely given up. (See Calkins, *Arch. für Entwickelungsmechanik*,
xv. 1902). R. Hertwig recently has advocated the view, that abnormal
relations between the amounts of nuclear and of protoplasmatic material
are rectified in some way by those processes. Teleologically, sexual
reproduction has been considered as a means of variability (Weismann),
but also as a means of preserving the type!

THE FIRST DEVELOPMENT PROCESS OF ECHINUS

Turning now definitively to the special kind of organism, chosen of our
type, the common sea-urchin, we properly begin with a few words about
the absolute size of its eggs and spermatozoa. All of you are familiar
with the eggs of birds and possibly of frogs; these are abnormally
large eggs, on account of the very high amount of reserve material they
contain. The almost spherical egg of our Echinus only measures about a
tenth of a millimetre in diameter; and the head of the spermatozoon has
a volume which is only the four-hundred-thousandth part of the volume
of the egg! The egg is about on the extreme limit of what can be seen
without optical instruments; it is visible as a small white point. But
the number of eggs produced by a single female is enormous and may
amount to hundreds of thousands; this is one of the properties which
render the eggs of Echinus so very suitable for experimental research;
you can obtain them whenever and in any quantity you like; and,
moreover, they happen to be very clear and transparent, even in later
stages, and to bear all kinds of operations well.

The spermia enters the egg, and it does so in the open water--another
of the experimental advantages of our type. Only one spermia enters
the egg in normal cases, and only its head goes in, the tail is left
outside. The moment that the head has penetrated the protoplasm of the
egg a thin membrane is formed by the latter. This membrane is very soft
at first, becoming much stronger later on; it is very important for all
experimental work, that by shaking the egg in the first minutes of its
existence the membrane can easily be destroyed without any damage to the
egg itself.

And now occurs the chief phenomenon of fertilisation: the nucleus of
the spermatozoon unites with the nucleus of the egg. When speaking of
maturation, we mentioned that half of the chromatin was thrown out of
the egg by that process: now this half is brought in again, but comes
from another individual.

It is from this phenomenon of nuclear union as the main character of
fertilisation that almost all theories of heredity assume their right to
regard the nuclei of the sexual cells as the true “seat” of inheritance.
Later on we shall have occasion to discuss this hypothesis from the
point of view of logic and fact.

After the complete union of what are called the male and the female
“pronuclei,” the egg begins its development; and this development, in
its first steps, is simply pure cell-division. We know already the chief
points of this process, and need only add to what has been described,
that in the whole first series of the cell-divisions of the egg, or,
to use the technical term, in the whole process of the “cleavage” or
“segmentation” of it, there is never any growth of the daughter-elements
after each division, such as we know to occur after all cell-divisions
of later embryological stages. So it happens, that during cleavage the
embryonic cells become smaller and smaller, until a certain limit is
reached; the sum of the volumes of all the cleavage cells together is
equal to the volume of the egg.

But our future studies will require a more thorough knowledge of the
cleavage of our Echinus; the experimental data we shall have to describe
later on could hardly be properly understood without such knowledge.
The first division plane, or, as we shall say, the first cleavage
plane, divides the eggs into equal parts; the second lies at right
angles to the first and again divides equally: we now have a ring of
four cells. The third cleavage plane stands at right angles to the
first two; it may be called an equatorial plane, if we compare the egg
with a globe; it also divides equally, and so we now find two rings,
each consisting of four cells, and one above the other. But now the
cell-divisions cease to be equal, at least in one part of the egg: the
next division, which leads from the eight- to the sixteen-cell stage of
cleavage, forms four rings, of four cells each, out of the two rings of
the eight-cell stage. Only in one half of the germ, in which we shall
call the upper one, or which we might call, in comparison with a globe,
the northern hemisphere, are cells of equal size to be found; in the
lower half of the egg four very small cells have been formed at one
“pole” of the whole germ. We call these cells the “micromeres,” that
is, the “small parts,” on the analogy of the term “blastomeres,” that
is, parts of the germ, which is applied to all the cleavage cells in
general. The place occupied by the micromeres is of great importance
to the germ as a whole: the first formation of real organs will start
from this point later on. It is sufficient thus fully to have studied
the cleavage of our Echinus up to this stage: the later cleavage stages
may be mentioned more shortly. All the following divisions are into
equal parts; there are no other micromeres formed, though, of course,
the cells derived from the micromeres of the sixteen-cell stage always
remain smaller than the rest. All the divisions are tangential; radial
cleavages never occur, and therefore the process of cleavage ends at
last in the formation of one layer of cells, which forms the surface
of a sphere; it is especially by the rounding-up of each blastomere,
after its individual appearance, that this real surface layer of cells
is formed, but, of course, the condition, that no radial divisions
occur, is the most important one in its formation. When 808 blastomeres
have come into existence the process of cleavage is finished; a sphere
with a wall of cells and an empty interior is the result. That only 808
cells are formed, and not, as might be expected, 1024, is due to the
fact that the micromeres divide less often than the other elements; but
speaking roughly, of course, we may say that there are ten steps of
cleavage-divisions in our form; 1024 being equal to 2^{10}.

We have learned that the first process of development, the cleavage, is
carried out by simple cell-division. A few cases are known, in which
cell-division during cleavage is accompanied by a specific migration of
parts of the protoplasm in the interior of the blastomeres, especially
in the first two or first four; but in almost all instances cleavage
is as simple a process of mere division as it is in our sea-urchin.
Now the second step in development, at least in our form, is a typical
histological performance: it gives a new histological feature to all
of the blastomeres: they acquire small cilia on their outer side and
with these cilia the young germ is able to swim about after it has left
its membrane. The germ may be called a “blastula” at this stage, as it
was first called by Haeckel, whose useful denominations of the first
embryonic stages may conveniently be applied, even if one does not agree
with most, or perhaps almost all, of his speculations (Fig. 2).

[Illustration: Fig. 2.--Early Development of Echinus, the Common
Sea-urchin.

*a.* Two cells.

*b.* Four cells.

*c.* Eight cells, arranged in two rings of four, above one another.

*d.* Sixteen cells, four “micromeres” formed at the “vegetative” pole.

*e.* Optical section of the “blastula,” a hollow sphere consisting of
about one thousand cells, each of them with a small cilium.]

It is important to notice that the formation of the “blastula” from the
last cleavage stage is certainly a process of organisation, and may also
be called a differentiation with regard to that stage. But there is in
the blastula no trace of one *part* of the germ becoming different with
respect to others of its parts. If development were to go on in this
direction alone, high organisatory complications might occur: but there
would always be only one sort of cells, arranged in a sphere; there
would be only one kind of what is called “tissue.”

But in fact development very soon loads to true differences of the
parts of the germ with respect to one another, and the next step of the
process will enable us to apply different denominations to the different
parts of the embryo.

At one pole of the swimming blastula, exactly at the point where the
descendants of the micromeres are situated, about fifty cells lose
contact with their neighbours and leave the surface of the globe, being
driven into the interior space of it. Not very much is known about the
exact manner in which these changes of cellular arrangement are carried
out, whether the cells are passively pressed by their neighbours, or
whether, perhaps, in a more active manner, they change their surface
conditions; therefore, as in most ontogenetic processes, the description
had best be made cautiously in fairly neutral or figurative words.

The cells which in the above manner have entered the interior of the
blastula are to be the foundation of important parts of the future
organism; they are to form its connective tissue, many of its muscles,
and the skeleton. “Mesenchyme,” *i.e.* “what has been infused into the
other parts,” is the technical name usually applied to these cells.
We now have to learn their definite arrangement. At first they lie
as a sort of heap inside the cell wall of the blastula, inside the
“blastoderm,” *i.e.* skin of the germ. But soon they move from one
another, to form a ring round the pole at which they entered, and on
this ring a process takes place which has a very important bearing upon
the whole type of the organisation of the germ. You will have noticed
that hitherto the germ with regard to its symmetry has been a monaxial
or radial formation; the cleavage stages and the blastula with its
mesenchyme were forms with two different poles, lying at the ends of one
single line, and round this line everything was arranged concentrically.
But now what is called “bilateral symmetry” is established; the
mesenchyme ring assumes a structure which can be symmetrically divided
only by one plane, but divided in such a way, that one-half of it is the
mirror image of the other. A figure shows best what has occurred, and
you will notice (Fig. 3) two masses of cells in this figure, which have
the forms of spherical triangles: it is in the midst of these triangles
that the skeleton of the larva *originates*. The germ had an upper and
a lower side before: it now has got an upper and lower, front and back,
*right and left* half; it now has acquired that symmetry of organisation
which our own body has; at least it has got it as far as its mesenchyme
is concerned.

[Illustration: Fig. 3.--Formation of Mesenchyme in Echinus.

*a.* Outlines of blastula, side-view; mesenchyme forms a heap of cells
at the “vegetative” pole.

*a*_1. Heap of mesenchyme-cells from above.

*b.* Mesenchyme-cells arranged in a ring round the vegetative pole.

*c.* Mesenchyme-cells arranged in a bilateral-symmetrical figure;
primordia of skeleton in the midst of two spherical triangles.]

We leave the mesenchyme for a while and study another kind of
organogenesis. At the very same pole of the germ where the mesenchyme
cells originated there is a long and narrow tube of cell growing in,
and this tube, getting longer and longer, after a few hours of growth
touches the opposite pole of the larva. The growth of this cellular tube
marks the beginning of the formation of the intestine, with all that
is to be derived from it. The larva now is no longer a blastula, but
receives the name of “gastrula” in Haeckel’s terminology; it is built
up of the three “germ-layers” in this stage. The remaining part of the
blastoderm is called “ectoderm,” or outer layer; the newly-formed tube,
“endoderm,” or inner layer; while the third layer is the “mesenchyme”
already known to us.

The endoderm itself is a radial structure at first, as was the whole
germ in a former stage, but soon its free end bends and moves against
one of the sides of the ectoderm, against that side of it where the two
triangles of the mesenchyme are to be found also. Thus the endoderm
has acquired bilateral symmetry just as the mesenchyme before, and
as in this stage the ectoderm also assumes a bilateral symmetry
in its form, corresponding with the symmetrical relations in the
endoderm and the mesenchyme, we now may call the whole of our larva a
bilateral-symmetrical organisation.

It cannot be our task to follow all the points of organogenesis of
Echinus in detail. It must suffice to state briefly that ere long a
second portion of the mesenchyme is formed in the larva, starting from
the free end of its intestine tube; that the formation of the so-called
“coelum” occurs by a sort of splitting off from this same original
organ; and that the intestine itself is divided into three parts of
different size and aspect by two circular sections.

But we must not, I think, dismiss the formation of the skeleton so
quickly. I told you already that the skeleton has its first origin in
the midst of the two triangular cell-masses of the mesenchyme; but what
are the steps before it attains its typical and complicated structure?
At the beginning a very small tetrahedron, consisting of carbonate of
calcium, is formed in each of the triangles; the four edges of the
tetrahedron are produced into thin rods, and by means of a different
organogenesis along each of these rods the typical formation of the
skeleton proceeds. But the manner in which it is carried out is very
strange and peculiar. About thirty of the mesenchyme cells are occupied
in the formation of skeleton substance on each side of the larva. They
wander through the interior space of the gastrula--which at this stage
is not filled with sea water but with a sort of gelatinous material--and
wander in such a manner that they always come to the right places, where
a part of the skeleton is to be formed; they form it by a process of
secretion, quite unknown in detail; one of them forms one part, one the
other, but what they form altogether, is one whole.

When the formation of the skeleton is accomplished, the typical larva
of our Echinus is built up; it is called the “pluteus” (Fig. 4). Though
it is far from being the perfect adult animal, it has an independent
life of its own; it feeds and moves about and does not go through any
important changes of form for weeks. But after a certain period of
this species of independent life as a “larva,” the changes of form it
undergoes again are most fundamental: it must be transformed into the
adult sea-urchin, as all of you know. There are hundreds and hundreds
of single operations of organogenesis to be accomplished before that
end is reached; and perhaps the strangest of all these operations is a
certain sort of growth, by which the symmetry of the animal, at least
in certain of its parts--not in all of them--is changed again from
bilateral to radial, just the opposite of what happened in the very
early stages.

[Illustration: Fig. 4.--Larval Development of Echinus.

*A.* The gastrula.

*B.* Later stage, bilateral-symmetrical. Intestine begins to divide
into three parts.

*C.* Pluteus larva. S = Skeleton. I = Intestine.]

But we cannot follow the embryology of our Echinus further here; and
indeed we are the less obliged to do so, since in all our experimental
work we shall have to deal with it only as far as to the pluteus larva.
It is impossible under ordinary conditions to rear the germs up to the
adult stages in captivity.

You now, I hope, will have a general idea at least of the processes
of which the individual development of an animal consists. Of course
the specific features leading from the egg to the adult are different
in each specific case, and, in order to make this point as clear as
possible, I shall now add to our description a few words about what may
be called a comparative descriptive embryology.

COMPARATIVE EMBRYOLOGY

Even the cleavage may present rather different aspects. There may be a
compact blastula, not one surrounded by only one layer of cells as in
Echinus; or bilaterality may be established as early as the cleavage
stage--as in many worms and in ascidians--and not so late as in Echinus.
The formation of the germ layers may go on in a different order and
under very different conditions: a rather close relative of our Echinus,
for instance, the starfish, forms first the endoderm and afterwards
the mesenchyme. In many cases there is no tube of cells forming the
“endoderm,” but a flat layer of cells is the first foundation of all the
intestinal organs: so it is in all birds and in the cuttlefish. And,
as all of you know, of course, there are very many animal forms which
have no proper “larval” stage: there is one in the frog, the well-known
“tadpole,” but the birds and mammals have no larvae; that is to say,
there is no special stage in the ontogeny of these forms which leads an
independent life for a certain time, as if it were a species by itself,
but all the ontogenetical stages are properly “embryonic”--the germ is
always an “embryo” until it becomes the perfect young organism. And you
also know that not all skeletons consist of carbonate of calcium, but,
that there are skeletons of silicates, as in Radiolaria, and of horny
substance, as in many sponges. And, indeed, if we were to glance at the
development of plants also, the differences would seem to us probably
so great that all the similarities would seem to disappear.

But there are similarities, nevertheless, in all development, and we
shall now proceed to examine what they are. As a matter of fact, it was
especially for their sake that we studied the ontogeny of a special
form in such detail; one always sees generalities better if one knows
the specific features of at least one case. What then are the features
of most general and far-reaching importance, which may be abstracted
from the individual history of our sea-urchin, checked always by the
teachings of other ontogenies, including those of plants?

THE FIRST STEPS OF ANALYTICAL MORPHOGENESIS

If we look back upon the long fight of the schools of embryologists in
the eighteenth century about the question whether individual development
was to be regarded as a real production of visible manifoldness or as
a simple growth of visibly pre-existing manifoldness, whether it was
“epigenesis” or “evolutio,” there can be no doubt, if we rely on all
the investigations of the last hundred and fifty years, that, taken in
the descriptive sense, the theory of epigenesis is right. Descriptively
speaking there *is* a production of visible manifoldness in the course
of embryology: that is our first and main result. Any one possessed of
an average microscope may any day convince himself personally that it is
true.

In fact, true epigenesis, in the descriptive sense of the term, does
exist. One thing is formed “after” the other; there is not a mere
“unfolding” of what existed already, though in a smaller form; there is
no “evolutio” in the old meaning of the word.

The word “evolution” in English usually serves to denote the theory of
descent, that is of a real relationship of all organisms. Of course we
are not thinking here of this modern and specifically English meaning of
the Latin word *evolutio*. In its ancient sense it means to a certain
degree just the opposite; it says that there is no formation of anything
new, no transformation, but simply growth, and this is promoted not for
the race but for the individual. Keeping well in mind these historical
differences in the meaning of the word “evolutio,” no mistakes, it seems
to me, can occur from its use. We now shall try to obtain a few more
particular results from our descriptive study of morphogenesis, which
are nevertheless of a general bearing, being real characteristics of
organic individual development, and which, though not calculated of
themselves to further the problem, will in any case serve to prepare for
a more profound study of it.

The totality of the line of morphogenetic facts can easily be resolved
into a great number of distinct processes. We propose to call these
“elementary morphogenetic processes”; the turning in of the endoderm
and its division into three typical parts are examples of them. If we
give the name “elementary organs” to the distinct parts of every stage
of ontogeny which are uniform in themselves and are each the result of
one elementary process in our sense, we are entitled to say that each
embryological stage consists of a certain number of elementary organs.
The mesenchyme ring, the coelum, the middle-intestine, are instances of
such organs. It is important to notice well that the word elementary is
always understood here with regard to visible morphogenesis proper and
does not apply to what may be called elementary in the physiological
sense. An elementary process in our sense is a very distinct act of
form-building, and an elementary organ is the result of every one of
such acts.

The elementary organs are typical with regard to their position and with
regard to their histological properties. In many cases they are of a
very clearly different histological type, as for instance, the cells of
the three so-called germ-layers; and in other cases, though apparently
almost identical histologically, they can be proved to be different
by their different power of resisting injuries or by other means. But
there are not as many different types of histological structure as there
are typically placed organs: on the contrary there are many elementary
organs of the same type in different typical parts of the organism, as
all of you know to be the case with nerves and muscles. It will not be
without importance for our future theory of development, carefully to
notice this fact, that specialisation in the *position* of embryonic
parts is more strict than in their histology.

But elementary organs are not only typical in position and histology,
they are typical also with regard to their form and their relative size.
It agrees with what has been said about histology being independent of
typical position, that there may be a number of organs in an embryonic
stage, all in their most typical positions, which though all possessing
the same histology, may have different forms or different sizes or
both: the single bones of the skeleton of vertebrates or of adult
echinoderms are the very best instances of this most important feature
of organogenesis. If we look back from elementary organs to elementary
processes, the specialisation of the size of those organs may also be
said to be the consequence of a typical duration of the elementary
morphogenetic process leading to them.[7]

[7] The phrase “*ceteris paribus*” has to be added of course, as the
duration of each single elementary morphogenetic process is liable to
vary with the temperature and many other conditions of the medium.

I hardly need to say, that the histology, form, and size of elementary
organs are equally an expression of their present or future
physiological function. At least they prepare for this function by a
specific sort of metabolism which sets in very early.

The whole sequence of individual morphogenesis has been divided by some
embryologists into two different periods; there is a first period,
during which the foundations of the organisation of the “type” are
laid down, and a second period, during which the histo-physiological
specifications are modelled out (von Baer, Götte, Roux). Such a
discrimination is certainly justified, if not taken too strictly; but
its practical application would encounter certain difficulties in many
larval forms, and also, of course, in all plants.

Our mention of plants leads us to the last of our analytical results. If
an animal germ proceeds in its development from a stage *d* to the stage
*g*, passing through *e* and *f*, we may say that the whole of *d* has
become the whole of *f*, but we cannot say that there is a certain part
of *f* which is *d*, we cannot say that *f* is *d* + *a*. But in plants
we can: the stage *f* is indeed equal to *a* + *b* + *c* + *d* + *e* +
*a* [Transcriber’s note: probable typo for *f*] in vegetable organisms;
all earlier stages are actually visible as parts of the last one. The
great embryologist, Carl Ernst von Baer, most clearly appreciated these
analytical differences between animal and vegetable morphogenesis. They
become a little less marked if we remember that plants, in a certain
respect, are not simple individuals but colonies, and that among the
corals, hydroids, bryozoa, and ascidia, we find analogies to plants in
the animal kingdom; but nevertheless the differences we have stated are
not extinguished by such reasoning. It seems almost wholly due to the
occurrence of so many foldings and bendings and migrations of cells and
complexes of cells in animal morphogenesis, that an earlier stage of
their development seems *lost* in the later one; those processes are
almost entirely wanting in plants, even if we study their very first
ontogenetic stages. If we say that almost all production of surfaces
goes on outside in plants, inside in animals, we shall have adequately
described the difference. And this feature again leads to the further
diversity between animals and plants which is best expressed by calling
the former “closed,” the latter “open” forms: animals reach a point
where they are finished, plants never are finished, at least in most
cases.

I hope you will allow that I have tried to draw from descriptive and
comparative embryology as many general analytical results as are
possibly to be obtained. It is not my fault if there are not any
more, nor is it my fault if the results reached are not of the most
satisfactory character. You may say that these results perhaps enable
you to see a little more clearly and markedly than before a few of the
characters of development, but that you have not really learnt anything
new. Your disappointment--my own disappointment--in our analysis is due
to the use of pure description and comparison as scientific methods.

THE LIMITS OF PURE DESCRIPTION IN SCIENCE

We have analysed our descriptions as far as we could, and now we must
confess that what we have found cannot be the last thing knowable
about individual morphogenesis. There must be something deeper to be
discovered: we only have been on the surface of the phenomena, we
now want to get to the very bottom of them. Why then occurs all that
folding, and bending, and histogenesis, and all the other processes we
have described? There must be something that drives them out, so to say.

There is a very famous dictum in the *Treatise on Mechanics* by the
late Gustav Kirchhoff, that it is the task of mechanics to describe
completely and in the most simple manner all the motions that occur in
nature. These words, which may appear problematic even in mechanics,
have had a really pernicious influence on biology. People were extremely
pleased with them. “‘Describing’--that is just what we always have
done,” they said; “now we see that we have done just what was right;
a famous physicist has told us so.” They did not see that Kirchhoff
had added the words “completely and in the most simple manner”; and
moreover, they did not consider that Kirchhoff never regarded it as the
ultimate aim of physics to describe thunderstorms or volcanic eruptions
or denudations; yet it only is with such “descriptions” that biological
descriptions of *given* bodies and processes are to be compared!

Physicists always have used both experiment and hypothetical
construction--Kirchhoff himself did so in the most gifted manner. With
these aids they have gone through the whole of the phenomena, and what
they found to be ultimate and truly elemental, that alone may they
be said to have “described”; but they have “explained” by the aid of
elementalities what proved to be not elemental in itself.[8]

[8] We shall not avoid in these lectures the word “explain”--so much
out of fashion nowadays. To “explain” means to subsume under known
concepts, or rules, or laws, or principles, whether the laws or concepts
themselves be “explained” or not. Explaining, therefore, is always
relative: what is elemental, of course, is only to be described, or
rather to be stated.

It is the *method* of the physicists--not their results--that
morphogenesis has to apply in order to make progress; and this method
we shall begin to apply in our next lectures. Physiology proper has
never been so short-sighted and self-satisfied as not to learn from
other sciences, from which indeed there was very much to be learned; but
morphology has: the bare describing and comparing of descriptions has
been its only aim for about forty years or more, and lines of descent of
a very problematic character were its only general results. It was not
seen that science had to begin, not with problematic events of the past,
but with what actually happens before our eyes.

But before saying any more about the exact rational and experimental
method in morphology, which indeed may be regarded as a new method,
since its prevalence in the eighteenth century had been really
forgotten, we first shall have to analyse shortly some general attempts
to understand morphogenesis by means of hypothetic construction
exclusively. Such attempts have become very important as points of
issue for really exact research, and, moreover, they deserve attention,
because they prove that their authors at least had not quite forgotten
that there were still other problems to be solved in morphology than
only phylogenetical ones.

*B.* EXPERIMENTAL AND THEORETICAL MORPHOGENESIS

1. THE FOUNDATIONS OF THE PHYSIOLOGY OF DEVELOPMENT. “EVOLUTIO” AND
“EPIGENESIS”

THE THEORY OF WEISMANN

Of all the purely hypothetic theories on morphogenesis that of August
Weismann[9] can claim to have had the greatest influence, and to
be at the same time the most logical and the most elaborated. The
“germ-plasma” theory of the German author is generally considered as
being a theory of heredity, and that is true inasmuch as problems of
inheritance proper have been the starting-point of all his hypothetic
speculations, and also form in some respect the most valuable part
of them. But, rightly understood, Weismann’s theory consists of two
independent parts, which relate to morphogenesis and to heredity
separately, and it is only the first which we shall have to take into
consideration at present; what is generally known as the doctrine of the
“continuity of the germ-plasm” will be discussed in a later chapter.

[9] *Das Keimplasma*, Jena, 1892.

Weismann assumes that a very complicated organised structure, below
the limits of visibility even with the highest optical powers, is the
foundation of all morphogenetic processes, in such a way that, whilst
part of this structure is handed over from generation to generation as
the basis of heredity, another part of it is disintegrated during the
individual development, and directs development by being disintegrated.
The expression, “part” of the structure, first calls for some
explanation. Weismann supposes several examples, several copies, as it
were, of his structure to be present in the germ cells, and it is to
these copies that the word “part” has been applied by us: at least one
copy has to be disintegrated during ontogeny.

The morphogenetic structure is assumed to be present in the nucleus
of the germ cells, and Weismann supposes the disintegration of his
hypothetic structure to be accomplished by nuclear division. By the
cleavage of the egg, the most *fundamental* parts of it are separated
one from the other. The word “fundamental” must be understood as
applying not to proper elements or complexes of elements of the
organisation, but to the chief relations of symmetry; the first
cleavage, for instance, may separate the right and the left part of
the structure, the second one its upper and lower parts, and after the
third or equatorial cleavage all the principal eighths of our minute
organisation are divided off: for the minute organisation, it must now
be added, had been supposed to be built up differently in the three
directions of space, just as the adult organism is. Weismann concedes it
to be absolutely unknown in what manner the proper relation between the
parts of the disintegrated fundamental morphogenetic structure and the
real processes of morphogenesis is realised; enough that there may be
imagined such a relation.

At the end of organogenesis the structure is assumed to have been
broken up into its elements, and these elements, which may be chemical
compounds, determine the fate of the single cells of the adult organism.

Here let us pause for a moment. There cannot be any doubt that
Weismann’s theory resembles to a very high degree the old “evolutio”
doctrines of the eighteenth century, except that it is a little less
crude. The chick itself is not supposed to be present in the hen’s egg
before development, and ontogeny is not regarded as a mere growth of
that chick in miniature, but what really is supposed to be present in
the egg is nevertheless a something that in all its parts corresponds
to all the parts of the chick, only under a somewhat different
aspect, while all the relations of the parts of the one correspond
to the relations of the parts of the other. Indeed, only on such an
hypothesis of a fairly fixed and rigid relation between the parts of
the morphogenetic structure could it be possible for the disintegration
of the structure to go on, not by parts of organisation, but by parts
of symmetry; which, indeed, is a very strange, but not an illogical,
feature of Weismann’s doctrine.

Weismann is absolutely convinced that there must be a theory of
“evolutio,” in the old sense of the word, to account for the ontogenetic
facts; that “epigenesis” has its place only in descriptive embryology,
where, indeed, as we know, manifoldness in the *visible* sense is
produced, but that epigenesis can never form the foundation of a real
morphogenetic *theory*: theoretically one pre-existing manifoldness is
transformed into the other. An epigenetic theory would lead right beyond
natural science, Weismann thinks, as in fact, all such theories, if
fully worked out, have carried their authors to vitalistic views. But
vitalism is regarded by him as dethroned for ever.

Under these circumstances we have a good right, it seems to me, to speak
of a *dogmatic* basis of Weismann’s theory of development.

But to complete the outlines of the theory itself: Weismann was
well aware that there were some grave difficulties attaching to his
statements: all the facts of so-called adventitious morphogenesis in
plants, of regeneration in animals, proved that the morphogenetic
organisation could not be fully disintegrated during ontogeny. But these
difficulties were not absolute: they could be overcome: indeed, Weismann
assumes, that in certain specific cases--and he regarded all cases of
restoration of a destroyed organisation as due to specific properties
of the subjects, originated by roundabout variations and natural
selection--that in specific cases, specific arrangements of minute parts
were formed during the process of disintegration, and were surrendered
to specific cells during development, from which regeneration or
adventitious budding could originate if required. “Plasma of reserve”
was the name bestowed on these hypothetic arrangements.

Almost independently another German author, Wilhelm Roux,[10] has
advocated a theoretical view of morphogenesis which very closely
resembles the hypothesis of Weismann. According to Roux a minute
ultimate structure is present in the nucleus of the germ and directs
development by being divided into its parts during the series of nuclear
divisions.

[10] *Die Bedeutung der Kernteilungsfiguren*, Leipzig, 1883.

But in spite of this similarity of the outset, we enter an altogether
different field of biological investigation on mentioning Roux’s name:
we are leaving hypothetic construction, at least in its absoluteness,
and are entering the realms of scientific experiment in morphology.

EXPERIMENTAL MORPHOLOGY

I have told you already in the last lecture that, while in the
eighteenth century individual morphogenesis had formed the centre of
biological interest and been studied experimentally in a thoroughly
adequate manner, that interest gradually diminished, until at last
the physiology of form as an exact separate science was almost wholly
forgotten. At least that was the state of affairs as regards zoological
biology; botanists, it must be granted, have never lost the historical
continuity to such a degree; botany has never ceased to be regarded
as one science and never was broken up into parts as zoology was.
Zoological physiology and zoological morphology indeed were for many
years in a relationship to one another not very much closer than the
relation between philology and chemistry.

There were always a few men, of course, who strove against the current.
The late Wilhelm His,[11] instance, described the embryology of the
chick in an original manner, in order to find out the mechanical
relations of embryonic parts, by which passive deformation, as an
integrating part of morphogenesis, might be induced. He also most
clearly stated the ultimate aim of embryology to be the mathematical
derivation of the adult form from the distribution of growth in the
germ. To Alexander Goette[12] we owe another set of analytical
considerations about ontogeny. Newport, as early as 1850, and in
later years Pflüger and Rauber, carried out experiments on the eggs
of the frog, which may truly be called anticipatory of what was to
follow. But it was Wilhelm Roux,[13] now professor of anatomy at
Halle, who entered the field with a thoroughly elaborated programme,
who knew not only how to state the problem analytically, but also
how to attack it, fully convinced of the importance of what he did.
“Entwickelungsmechanik,”--mechanics of development--he called the “new
branch of anatomical science” of which he tried to lay the foundations.

[11] *Unsere Körperform*, Leipzig, 1875.

[12] *Die Entwickelungsgeschichte der Unke*, Leipzig, 1875.

[13] *Gesammelte Abhandlungen*, Leipzig, 1895. Most important
theoretical papers:--*Zeitschr. Biolog.* 21, 1885; *Die
Entwickelungsmechanik der Organismen*, Wien, 1890; *Vorträge und
Aufsätze über Entwickelungsmechanik*, Heft i., Leipzig, 1905.

I cannot let this occasion pass without emphasising in the most decided
manner how highly in my opinion Roux’s services to the systematic
exploration of morphogenesis must be esteemed. I feel the more obliged
to do so, because later on I shall have to contradict not only many
of his positive statements but also most of his theoretical views. He
himself has lately given up much of what he most strongly advocated only
ten years ago. But Roux’s place in the history of biological science can
never be altered, let science take what path it will.

It is not the place here to develop the logic of experiment; least of
all is it necessary in the country of John Stuart Mill. All of you know
that experiment, by its method of isolating the single constituents
of complicated phenomena, is the principal aid in the discovery of
so-called causal relations. Let us try then to see what causal
relations Wilhelm Roux established with the aid of morphogenetic
experiment.

THE WORK OF WILHELM ROUX

We know already that an hypothesis about the foundation of individual
development was his starting-point. Like Weismann he supposed that
there exists a very complicated structure in the germ, and that nuclear
division leads to the disintegration of that structure. He next tried to
bring forward what might be called a number of indicia supporting his
view.

A close relation had been found to exist in many cases between the
direction of the first cleavage furrows of the germ and the direction
of the chief planes of symmetry in the adult: the first cleavage, for
instance, very often corresponds to the median plane, or stands at right
angles to it. And in other instances, such as have been worked out into
the doctrine of so-called “cell-lineages,” typical cleavage cells were
found to correspond to typical organs. Was not that a strong support
for a theory which regarded cellular division as the principal means
of differentiation? It is true, the close relations between cleavage
and symmetry did not exist in every case, but then there had always
happened some specific experimental disturbances, *e.g.* influences of
an abnormal direction of gravity on account of a turning over of the
egg, and it was easy to reconcile such cases with the generally accepted
theory on the assumption of what was called “anachronism” of cleavage.

But Roux was not satisfied with mere indicia, he wanted a proof, and
with this intention he carried out an experiment which has become
very celebrated.[14] With a hot needle he killed one of the first two
blastomeres of the frog’s egg after the full accomplishment of its first
cleavage, and then watched the development of the surviving cell. A
typical half-embryo was seen to emerge--an organism indeed, which was as
much a half as if a fully formed embryo of a certain stage had been cut
in two by a razor. It was especially in the anterior part of the embryo
that its “halfness” could most clearly be demonstrated.

[14] *Virchow’s Archiv.* 114, 1888.

That seemed to be a proof of Weismann’s and Roux’s theory of
development, a proof of the hypothesis that there is a very complicated
structure which promotes ontogeny by its disintegration, carried out
during the cell divisions of embryology by the aid of the process of
nuclear division, the so-called “karyokinesis.”

To the dispassionate observer it will appear, I suppose, that the
conclusions drawn by Roux from his experiment go a little beyond their
legitimate length. Certainly some sort of “evolutio” is proved by
rearing half the frog from half the egg. But is anything proved, is
there anything discovered at all about the nucleus? It was only on
account of the common opinion about the part it played in morphogenesis
that the nucleus had been taken into consideration.

Things soon became still more ambiguous.

THE EXPERIMENTS ON THE EGG OF THE SEA-URCHIN

Roux’s results were published for the first time in 1888; three years
later I tried to repeat his fundamental experiment on another subject
and by a somewhat different method. It was known from the cytological
researches of the brothers Hertwig and Boveri that the eggs of the
common sea-urchin (*Echinus microtuberculatus*) are able to stand well
all sorts of rough treatment, and that, in particular, when broken into
pieces by shaking, their fragments will survive and continue to segment.
I took advantage of these facts for my purposes. I shook the germs
rather violently during their two-cell stage, and in several instances I
succeeded in killing one of the blastomeres, while the other one was not
damaged, or in separating the two blastomeres from one another.[15]

[15] *Zeitschr. wiss. Zool.* 53, 1891.

Let us now follow the development of the isolated surviving cell. It
went through cleavage just as it would have done in contact with its
sister-cell, and there occurred cleavage stages which were just half
of the normal ones. The stage, for instance, which corresponded to the
normal sixteen-cell stage, and which, of course, in my subjects was
built up of eight elements only, showed two micromeres, two macromeres
and four cells of medium size, exactly as if a normal sixteen-cell stage
had been cut in two; and the form of the whole was that of a hemisphere.
So far there was no divergence from Roux’s results.

The development of our Echinus proceeds rather rapidly, the cleavage
being accomplished in about fifteen hours. I now noticed on the evening
of the first day of the experiment, when the half-germ was composed of
about two hundred elements, that the margin of the hemispherical germ
bent together a little, as if it were about to form a whole sphere
of smaller size, and, indeed, the next morning a *whole* diminutive
blastula was swimming about. I was so much convinced that I should get
Roux’s morphogenetical result in all its features that, even in spite of
this whole blastula, I now expected that the next morning would reveal
to me the half-organisation of my subject once more; the intestine, I
supposed, might come out quite on one side of it, as a half-tube, and
the mesenchyme ring might be a half one also.

But things turned out as they were bound to do and not as I had
expected; there was a typically *whole* gastrula on my dish the next
morning, differing only by its small size from a normal one; and this
*small but whole* gastrula was followed by a whole and typical small
pluteus-larva (Fig. 5).

[Illustration: Fig. 5.--Illustration of Experiments on Echinus.

*a*_1 and *b*_1. Normal gastrula and normal pluteus.

*a*_2 and *b*_2. “Half”-gastrula and “half”-pluteus, that *ought* to result
from one of the first two blastomeres, when isolated, according to the
theory of “evolutio.”

*a*_3 and *b*_3. The small *but whole* gastrula and pluteus that actually
*do* result.]

That was just the opposite of Roux’s result: one of the first two
blastomeres had undergone a half-cleavage as in his case, but then it
had become a whole organism by a simple process of rearrangement of its
material, without anything that resembled regeneration, in the sense of
a completion by budding from a wound.

If one blastomere of the two-cell stage was thus capable of performing
the morphogenetical process in its totality, it became, of course,
*impossible* to allow that nuclear division had separated any sort of
“germ-plasm” into two different halves, and not even the protoplasm of
the egg could be said to have been divided by the first cleavage furrow
into unequal parts, as the postulate of the strict theory of so-called
“evolutio” had been. This was a very important result, sufficient
alone to overthrow at once the theory of ontogenetical “evolutio,”
the “Mosaiktheorie” as it had been called--not by Roux himself, but
according to his views--in its exclusiveness.

After first widening the circle of my observations by showing that
one of the first four blastomeres is capable of performing a whole
organogenesis, and that three of the first four blastomeres together
result in an absolutely perfect organism, I went on to follow up
separately one of the two fundamental problems which had been suggested
by my first experiment: was there anything more to find out about
the importance or unimportance of the single *nuclear* divisions in
morphogenesis?[16]

[16] *Zeitschr. wiss. Zool.* 55, 1892.

By raising the temperature of the medium or by diluting the sea-water to
a certain degree it proved at first to be possible to alter in a rather
fundamental way the type of the cleavage-stages without any damage to
the resulting organism. There may be no micromeres at the sixteen-cell
stage, or they may appear as early as in the stage of eight cells;
no matter, the larva is bound to be typical. So it certainly is not
necessary for all the cleavages to occur just in their normal order.

But of greater importance for our purposes was what followed. I
succeeded in pressing the eggs of Echinus between two glass plates,
rather tightly, but without killing them; the eggs became deformed to
comparatively flat plates of a large diameter. Now in these eggs all
nuclear division occurred at right angles to the direction of pressure,
that is to say, in the direction of the plates, as long as the pressure
lasted; but the divisions began to occur at right angles to their former
direction, as soon as the pressure ceased. By letting the pressure be
at work for different times I therefore, of course, had it quite in my
power to obtain cleavage types just as I wanted to get them. If, for
instance, I kept the eggs under pressure until the eight-cell stage was
complete, I got a plate of eight cells one beside the other, instead of
two rings, of four cells each, one above the other, as in the normal
case; but the next cell division occurred at right angles to the former
ones, and a sixteen-cell stage, of two plates of eight cells each, one
above the other, was the result. If the pressure continued until the
sixteen-cell stage was reached, sixteen cells lay together in one plate,
and two plates of sixteen cells each, one above the other, were the
result of the next cleavage.

We are not, however, studying these things for cytological, but for
morphogenetical purposes, and for these the cleavage phenomenon itself
is less important than the organogenetic result of it: all our subjects
resulted in *absolutely normal* organisms. Now, it is clear, that the
spatial relations of the different nuclear divisions to each other are
anything but normal, in the eggs subjected to the pressure experiments;
that, so to say, every nucleus has got quite different neighbours if
compared with the “normal” case. If that makes no difference, then
there *cannot* exist any close relation between the single nuclear
divisions and organogenesis at all, and the conclusion we have drawn
more provisionally from the whole development of isolated blastomeres
has been extended and proved in the most perfect manner. There ought to
result a morphogenetic chaos according to the theory of real “evolutio”
carried out by nuclear division, if the positions of the single nuclei
were fundamentally changed with regard to one another (Fig. 6). But now
there resulted not chaos, but the normal organisation: therefore it was
disproved in the strictest way that nuclear divisions have any bearing
on the origin of organisation; at least as far as the divisions during
cleavage come into account.

[Illustration: Fig. 6.--Pressure-experiments on Echinus.

*a*_1 and *b*_1. Two normal cleavage stages, consisting of eight and
sixteen cells.

*a*_2 and *b*_2. Corresponding stages modified by exerting pressure
until the eight-cell stage was finished. See text.]

On the egg of the frog (O. Hertwig), and on the egg of annelids (E. B.
Wilson), my pressure experiments have been carried out with the same
result.[17]

[17] In the pressure experiments I had altered the relative position of
the nuclei *in origine*. In later years I succeeded in disturbing the
arrangement of the fully formed cells of the eight-cell stage, and in
getting normal larvæ in spite of that in many cases. But as this series
of experiments is not free from certain complications--which in part
will be understood later on (see page 73)--it must suffice here to have
mentioned them. (For further information see my paper in *Archiv. f.
Entwickelungsmechanik*, xiv., 1902, page 500.)

ON THE INTIMATE STRUCTURE OF THE PROTOPLASM OF THE GERM

Nuclear division, as we have seen, cannot be the basis of organogenesis,
and all we know about the whole development of isolated blastomeres
seems to show that there exists nothing responsible for differentiation
in the protoplasm either.

But would that be possible? It cannot appear possible on a more profound
consideration of the nature of morphogenesis, it seems to me: as the
untypical agents of the medium cannot be responsible in any way for
the origin of a form combination which is most typical and specific,
there must be somewhere in the egg itself a certain factor which is
responsible at least for the general orientation and symmetry of it.
Considerations of this kind led me, as early as 1893,[18] to urge the
hypothesis that there existed, that there *must* exist, a sort of
intimate structure in the egg, including polarity and bilaterality as
the chief features of its symmetry, a structure which belongs to every
smallest element of the egg, and which might be imagined by analogy
under the form of elementary magnets.[19] This hypothetic structure
could have its seat in the protoplasm only. In the egg of echinoderms it
would be capable of such a quick rearrangement after being disturbed,
that it could not be observed but only inferred logically; there might,
however, be cases in which its real discovery would be possible. Indeed
Roux’s frog-experiment seems to be a case where it is found to be at
work: at least it seems very probable to assume that Roux obtained half
of a frog’s embryo because the protoplasm of the isolated blastomere had
preserved the “halfness” of its intimate structure, and had not been
able to form a small whole out of it.

[18] *Mitteil. Neapel. 11, 1893.*

[19] But the elementary magnets would have to be bilateral!

Of course it was my principal object to verify this hypothesis, and
such verification became possible in a set of experiments which my
friend T. H. Morgan and myself carried out together,[20] in 1895, on
the eggs of ctenophores, a sort of pelagic animals, somewhat resembling
the jelly-fish, but of a rather different inner organisation. The
zoologist Chun had found even before Roux’s analytical studies, that
isolated blastomeres of the ctenophore egg behave like parts of the
whole and result in a half-organisation like the frog’s germ does. Chun
had not laid much stress on his discovery, which now, of course, from
the new points of view, became a very important one. We first repeated
Chun’s experiment and obtained his results, with the sole exception
that there was a tendency of the endoderm of the half-larva of Beroë
to become more than “half.” But that was not what we chiefly wanted to
study. We succeeded in cutting away a certain mass of the protoplasm
of the ctenophore egg just before it began to cleave, without damaging
its nuclear material in any way: in all cases, where the cut was
performed at the side, there resulted a certain type of larvae from
our experiments which showed exactly the same sort of defects as were
present in larvae developed from one of the first two blastomeres alone.

[20] *Arch. Entw. Mech.* 2, 1895.

The hypothesis of the morphogenetic importance of *protoplasm* had thus
been proved. In our experiments there was all of the nuclear material,
but there were defects on one side of the protoplasm of the egg; and the
defects in the adult were found to correspond to these defects in the
protoplasm.

And now O. Schultze and Morgan succeeded in performing some experiments
which directly proved the hypothesis of the part played by protoplasm
in the subject employed by Roux, *viz.*, the frog’s egg. The first of
these investigators managed to rear two whole frog embryos of small
size, if he slightly pressed the two-cell stage of that form between
two plates of glass and turned it over; and Morgan,[21] after having
killed one of the first two blastomeres, as was done in the original
experiment of Roux, was able to bring the surviving one to a half or
to a whole development according as it was undisturbed or turned.
There cannot be any doubt that in both of these cases, it is the
possibility of a rearrangement of protoplasm, offered by the turning
over, which allows the isolated blastomere to develop as a whole. The
regulation of the frog’s egg, with regard to its becoming whole, may be
called facultative, whilst the same regulation of the egg of Echinus
is obligatory. It is not without interest to note that the first two
blastomeres of the common newt, *i.e.* of a form which belongs to the
other class of Amphibia, after a separation of *any* kind, *always*
develop as wholes, their faculty of regulation being obligatory, like
that of Echinus.

[21] *Anat. Anz.* 10, 1895.

Whole or partial development may thus be dependent on the power of
regulation contained in the intimate polar-bilateral structure of the
protoplasm. Where this is so, the regulation and the differences in
development are both connected with the chief relations of symmetry.
The development becomes a half or a quarter of the normal because
there is only one-half or one-quarter of a certain structure present,
one-half or one-quarter with regard to the very wholeness of this
structure; the development is whole, in spite of disturbances, if
the intimate structure became whole first. We may describe the
“wholeness,” “halfness,” or “quarterness” of our hypothetic structure
in a mathematical way, by using three axes, at right angles to one
another, as the base of orientation. To each of these, *x*, *y*, and
*z*, a certain specific state with regard to the symmetrical relations
corresponds; thence it follows that, if there are wanting all those
parts of the intimate structure which are determined, say, by a negative
value of *y*, by minus *y*, then there is wanting half of the intimate
structure; and this halfness of the intimate structure is followed by
the halfness of organogenesis, the dependence of the latter on the
intimate structure being established. But if regulation has restored,
on a smaller scale, the whole of the arrangement according to all values
of *x*, *y* and *z*, development also can take place completely (Fig. 7).

[Illustration: Fig. 7.--Diagram illustrating the intimate Regulation of
Protoplasm from “Half” to “Whole.”

The large circle represents the original structure of the egg. In all
cases where cleavage-cells of the two-cell stage are isolated this
original structure is only present as “half” in the beginning, say
only on the right (+*y*) side. Development then becomes “half,” if the
intimate structure remains half; but it becomes “whole” (on a smaller
scale) if a new whole-structure (small circle!) is formed by regulatory
processes.]

I am quite aware that such a discussion is rather empty and purely
formal, nevertheless it is by no means without value, for it shows
most clearly the differences between what we have called the intimate
structure of germs, responsible only for the general symmetry of
themselves and of their isolated parts, and another sort of possible
structure of the egg-protoplasm which we now shall have to consider, and
which, at the first glance, seems to form a serious difficulty to our
statements, as far at least as they claim to be of general importance.
The study of this other sort of germinal structure at the same time will
lead us a step farther in our historical sketch of the first years of
“Entwickelungsmechanik” and will bring this sketch to its end.

ON SOME SPECIFICITIES OF ORGANISATION IN CERTAIN GERMS

It was known already about 1890, from the careful study of what has
been called “cell-lineage,” that in the eggs of several families of
the animal kingdom the origin of certain organs may be traced back to
individual cells of cleavage, having a typical histological character
of their own. In America especially such researches have been carried
out with the utmost minuteness, E. B. Wilson’s study of the cell-lineage
of the Annelid *Nereis* being the first of them. If it were true that
nuclear division is of no determining influence upon the ontogenetic
fate of the blastomeres, only peculiarities of the different parts of
the protoplasm could account for such relations of special cleavage
cells to special organs. I advocated this view as early as in 1894,
and it was proved two years later by Crampton, a pupil of Wilson’s,
in some very fine experiments performed on the germ of a certain
mollusc.[22] The egg of this form contains a special sort of protoplasm
near its vegetative pole, and this part of it is separated at each
of the first two segmentations by a sort of pseudo-cleavage, leading
to stages of three and five separated masses instead of two and four,
the supernumerary mass being the so-called “yolk-sac” and possessing
no nuclear elements (Fig. 8). Crampton removed this yolk-sac at the
two-cell stage, and he found that the cleavage of the germs thus
operated upon was normal except with regard to the size and histological
appearance of one cell, and that the larvae originating from these
germs were complete in every respect except in their mesenchyme, which
was wanting. A special part of the protoplasm of the egg had thus been
brought into relation with quite a special part of organisation, *and
that special part of the protoplasm contained no nucleus*.

[22] *Arch. Entw. Mech.* 3, 1896.

[Illustration: Fig. 8.--The Mollusc Dentalium (*after* E. B. Wilson).

*a.* The egg, consisting of three different kinds of protoplasmatic
material.

*b.* First cleavage-stage. There are two cells and one “pseudo-cell,”
the yolk-sac, which contains no nucleus. This was removed in Crampton’s
experiment.]

GENERAL RESULTS OF THE FIRST PERIOD OF “ENTWICKELUNGSMECHANIK”

This experiment of Crampton’s, afterwards confirmed by Wilson himself,
may be said to have closed the first period of the new science of
physiology of form, a period devoted almost exclusively to the problem
whether the theory of nuclear division or, in a wider sense, whether the
theory of a strict “evolutio” as the basis of organogenesis was true or
not.

It was shown, as we have seen, that the theory of the “qualitatively
unequal nuclear division” (“qualitativ-ungleiche Kernteilung” in German)
certainly was not true, and that there also was no strict “evolutio”
in protoplasm. Hence Weismann’s theory was clearly disproved. There
certainly is a good deal of real “epigenesis” in ontogeny, a good deal
of “production of manifoldness,” not only with regard to visibility but
in a more profound meaning. But some sort of pre-formation had also
been proved to exist, and this pre-formation, or, if you like, this
restricted evolution, was found to be of two different kinds. First an
intimate organisation of the protoplasm, spoken of as its polarity and
bilaterality, was discovered, and this had to be postulated for every
kind of germs, even when it was overshadowed by immediate obligatory
regulation after disturbances. Besides that there were cases in which
a real specificity of special parts of the germ existed, a relation of
these special parts to special organs: but this sort of specification
also was shown to belong to the protoplasm.

It follows from all we have mentioned about the organisation of
protoplasm and its bearing on morphogenesis, that the eggs of different
animals may behave rather differently, in this respect, and that
the eggs indeed may be classified according to the degree of their
organisation. Though we must leave a detailed discussion of these
topics to morphology proper, we yet shall try shortly to summarise
what has been ascertained about them in the different classes of the
animal kingdom. A full regulation of the *intimate* structure of
isolated blastomeres to a new whole, has been proved to exist in the
highest degree in the eggs of all echinoderms, medusae, nemertines,
Amphioxus, fishes, and in one class of the Amphibia (the *Urodela*);
it is facultative only among the other class of Amphibia, the *Anura*,
and seems to be only partly developed or to be wanting altogether among
ctenophora, ascidia, annelids, and mollusca. Peculiarities in the
organisation of *specific parts* of protoplasm have been proved to occur
in more cases than at first had been assumed; they exist even in the
echinoderm egg, as experiments of the last few years have shown; even
here a sort of specification exists at the vegetative pole of the egg,
though it is liable to a certain kind of regulation; the same is true in
medusae, nemertines, etc.; but among molluscs, ascidians, and annelids
no regulation about the specific organisation of the germ in cleavage
has been found in any case.

The differences in the degree of regulability of the intimate germinal
structure may easily be reduced to simple differences in the physical
consistency of their protoplasm.[23] But all differences in specific
organisation must remain as they are for the present; it will be one of
the aims of the future theory of development to trace these differences
also to a common source.

[23] It deserves notice in this connection, that in some cases the
protoplasm of parts of a germ has been found to be more regulable in
the earliest stages, when it is very fluid, than later, when it is more
stiff.

That such an endeavour will probably be not without success, is clear,
I should think, from the mere fact that differences with regard to
germinal specific pre-formation do not agree in any way with the
systematic position of the animals exhibiting them; for, strange as it
would be if there were two utterly different kinds of morphogenesis, it
would be still more strange if there were differences in morphogenesis
which were totally unconnected with systematic relationship: the
ctenophores behaving differently from the medusae, and Amphioxus
differently from ascidians.

SOME NEW RESULTS CONCERNING RESTITUTIONS

We now might close this chapter, which has chiefly dealt with the
disproof of a certain sort of ontogenetic theories, and therefore
has been almost negative in its character, did it not seem desirable
to add at least a few words about the later discoveries relating to
morphogenetic restorations of the adult. We have learnt that Weismann
created his concept of “reserve plasma” to account for what little
he knew about “restitutions”: that is, about the restoration of lost
parts: he only knew regeneration proper in animals and the formation of
adventitious buds in plants. It is common to both of these phenomena
that they take their origin from typically localised points of the body
in every case; each time they occur a certain well-defined part of the
body is charged with the restoration of the lost parts. To explain
such cases Weismann’s hypothesis was quite adequate, at least in a
logical sense. But at present, as we shall discuss more fully in another
chapter, we know of some very widespread forms of restitution, in which
what is to be done for a replacement of the lost is not entrusted to
*one* typical part of the body in every case, but in which the whole
of the morphogenetic action to be performed is transferred in its
*single* parts to the *single* parts of the body which is accomplishing
restoration: each of its parts has to take an individual share in the
process of restoration, effecting what is properly called a certain kind
of “re-differentiation” (“Umdifferenzierung”), and this share varies
according to the relative position of the part in each case. Later on
these statements will appear in more correct form than at present, and
then it will become clear that we are fully entitled to emphasise at the
end of our criticism of Weismann’s theory, that his hypothesis relating
to restorations can be no more true than his theory of development
proper was found to be.

And now we shall pass on to our positive work.

We shall try to sketch the outlines of what might properly be called an
*analytical theory of morphogenesis*; that is, to explain the sum of our
knowledge about organic form-production, gained by experiment and by
logical analysis, in the form of a real system, in which each part will
be, or at least will try to be, in its proper place and in relation with
every other part. Our analytical work will give us ample opportunity of
mentioning many important topics of so-called general physiology also,
irrespective of morphogenesis as such. But morphogenesis is always to
be the centre and starting-point of our analysis. As I myself approach
the subject as a zoologist, animal morphogenesis, as before, will be the
principal subject of what is to follow.

2. ANALYTICAL THEORY OF MORPHOGENESIS[24]

[24] Compare my *Analytische Theorie der organischen Entwickelung*,
Leipzig, 1894, and my reviews in *Ergebnisse der Anatomie und
Entwickelungsgeschichte*, vols. viii. xi. xiv., 1899-1905. A shorter
review is given in *Ergebnisse der Physiologie*, vol. v., 1906. The full
literature will be found in these reviews.

α. THE DISTRIBUTION OF MORPHOGENETIC POTENCIES

*Prospective Value and Prospective Potency*

Wilhelm Roux did not fail to see that the questions of the locality and
the time of all morphogenetic differentiations had to be solved first,
before any problem of causality proper could be attacked. From this
point of view he carried out his fundamental experiments.

It is only in terminology that we differ from his views, if we prefer
to call our introductory chapter an analysis of the distribution of
morphogenetic potencies. The result will be of course rather different
from what Roux expected it would be.

Let us begin by laying down two fundamental concepts. Suppose we have
here a definite embryo in a definite state of development, say a
blastula, or a gastrula, or some sort of larva, then we are entitled
to study any special element of any special elementary organ of this
germ with respect to what is actually to develop out of this very
element in the future actual course of this development, whether it be
undisturbed or disturbed in any way; it is, so to say, the actual, *the
real fate* of our element, that we take in account. I have proposed to
call this real fate of each embryonic part in this very definite line
of morphogenesis its *prospective value* (“prospective Bedeutung” in
German). The fundamental question of the first chapter of our analytical
theory of development may now be stated as follows: Is the prospective
value of each part of any state of the morphogenetic line constant,
*i.e.* is it unchangeable, can it be nothing but one; or is it variable,
may it change according to different circumstances?

We first introduce a second concept: the term *prospective potency*
(“prospective Potenz” in German) of each embryonic element. The term
“prospective morphogenetic potency” is to signify the *possible
fate* of each of those elements. With the aid of our two artificial
concepts we are now able to formulate our introductory question thus:
Is the prospective potency of each embryonic part fully given by
its prospective value in a certain definite case; is it, so to say,
identical with it, or does the prospective potency contain more than the
prospective value of an element in a certain case reveals?

We know already from our historical sketch that the latter is true: that
the actual fate of a part need not be identical with its possible fate,
at least in many cases; that the potency of the first four blastomeres
of the egg of the sea-urchin, for instance, has a far wider range than
is shown by what each of them actually performs in even this ontogeny.
There are more morphogenetic possibilities contained in each embryonic
part than are actually realised in a special morphogenetic case.

As the most important special morphogenetic case is, of course, the
so-called “normal” one, we can also express our formula in terms of
special reference to it: there are more morphogenetic possibilities in
each part than the observation of the normal development can reveal.
Thus we have at once justified the application of analytical experiment
to morphogenesis, and have stated its most important results.

As the introductory experiments about “Entwickelungsmechanik” have shown
already that the prospective potency of embryonic parts, at least in
certain cases, *can* exceed their prospective value--that, at least in
certain cases, it can be different from it--the concept of prospective
potency at the very beginning of our studies puts itself in the centre
of analytical interest, leaving to the concept of prospective value the
second place only. For that each embryonic part actually has a certain
prospective value, a specified actual fate in every single case of
ontogeny, is clear from itself and does not affirm more than the reality
of morphogenetic cases in general; but that the prospective value of the
elements may change, that there is a morphogenetic power in them, which
contains more than actuality; in other words, that the term “prospective
potency” has not only a logical but a factual interest: all these points
amount to a statement not only of the most fundamental introductory
results but also of the actual *problems* of the physiology of form.

If at each point of the germ something else *can* be formed than
actually is formed, why then does there happen in each case just what
happens and nothing else? In these words indeed we may state the chief
problem of our science, at least after the fundamental relation of
the superiority of prospective potency to prospective value has been
generally shown.

We consequently may shortly formulate our first problem as the question
of the distribution of the prospective morphogenetic potencies in the
germ. Now this general question involves a number of particular ones.
Up to what stage, if at all, is there an absolutely equal distribution
of the potencies over all the elements of the germ? When such an equal
distribution has ceased to exist at a certain stage, what are then the
relations between the parts of different potency? How, on the other
hand, does a newly arisen, more specialised sort of potency behave with
regard to the original general potency, and what about the distribution
of the more restricted potency?

I know very well that all such questions will seem to you a little
formal, and, so to say, academical at the outset. We shall not fail to
attach to them very concrete meanings.

*The Potencies of the Blastomeres*

At first we turn back to our experiments on the egg of the sea-urchin
as a type of the germ in the very earliest stages. We know already that
each of the first two, or each of the first four, or three of the first
four blastomeres together may produce a whole organism. We may add that
the swimming blastula, consisting of about one thousand cells, when cut
in two quite at random, in a plane coincident with, or at least passing
near, its polar axis, may form two fully developed organisms out of its
halves.[25] We may formulate this result in the words: the prospective
potency of the single cells of a blastula of Echinus is the same for
all of them; their prospective value is as far as possible from being
constant.

[25] If the plane of section passes near the equator of the germ, two
whole larvae may be formed also, but in the majority of cases the
“animal” half does not go beyond the blastula. The specific features of
the organisation of the protoplasm come into account here. See also page
65, note 1.

But we may say even a little more: what actually will happen in each of
the blastula cells in any special case of development experimentally
determined depends on the position of that cell in the whole, if the
“whole” is put into relation with any fixed system of co-ordinates; or
more shortly, “the prospective value of any blastula cell is a function
of its position in the whole.”

I know from former experience that this statement wants a few words of
explanation. The word “function” is employed here in the most general,
mathematical sense, simply to express that the prospective value,
the actual fate of a cell, will change, whenever its position in the
whole is different.[26] The “whole” may be related to any three axes
drawn through the normal undisturbed egg, on the hypothesis that there
exists a primary polarity and bilaterality of the germ; the axes which
determine this sort of symmetry may, of course, conveniently be taken as
co-ordinates; but that is not necessary.

[26] A change of the position of the cell is of course effected by each
variation of the direction of the cut, which is purely a matter of
chance.

*The Potencies of Elementary Organs in General*

Before dealing with other very young germs, I think it advisable to
describe first an experiment which is carried out at a later stage of
our well-known form. This experiment will easily lead to a few new
concepts, which we shall want later on, and will serve, on the other
hand, as a basis of explanation for some results, obtained from the
youngest germs of some other animal species, which otherwise would seem
to be rather irreconcilable with what our Echinus teaches us.

You know, from the second lecture, what a gastrula of our sea-urchin
is. If you bisect this gastrula, when it is completely formed, or
still better, if you bisect the gastrula of the starfish, either along
the axis or at right angles to it, you get complete little organisms
developed from the parts: the ectoderm is formed in the typical manner
in the parts, and so is the endoderm; everything is proportionate and
only smaller than in the normal case. So we have at once the important
results, that, as in the blastula, so in the ectoderm and in the
endoderm of our Echinus or of the starfish, the prospective potencies
are the same for every single element: both in the ectoderm and in
the endoderm the prospective value of each cell is a “function of its
position” (Fig. 9).

[Illustration: Fig. 9.--The Starfish, *Asterias*.

*a*^1. Normal gastrula; may be bisected along the main axis or at right
angles to it (see dotted lines).

*a*^2. Normal larva, “*Bipinnaria*.”

*b*^1. Small but whole gastrula that results by a process of regulation
from the parts of a bisected gastrula.

*b*^2. Small *but whole* “*Bipinnaria*,” developed out of *b*^1.]

But a further experiment has been made on our gastrula. If at the moment
when the material of the future intestine is most distinctly marked in
the blastoderm, but not yet grown into a tube, if at this moment the
upper half of the larva is separated from the lower by an equatorial
section, you will get a complete larva only from that part which bears
the “Anlage” of the endoderm, while the other half will proceed in
morphogenesis very well but will form only ectodermal organs. By another
sort of experiment, which we cannot fully explain here, it has been
shown that the endoderm if isolated is also only able to form such
organs as are normally derived from it.

And so we may summarise both our last results by saying: though
ectoderm and endoderm have their potencies equally distributed amongst
their respective cells, they possess different potencies compared one
with the other. And the same relation is found to hold for all cases of
what we call elementary organs: they are “equipotential,” as we may say,
in themselves, but of different potencies compared with each other.

*Explicit and Implicit Potencies: Primary and Secondary Potencies*

We shall first give to our concept of “prospective potency” a few words
of further analytical explanation with the help of our newly obtained
knowledge.

It is clear from what we have stated that the prospective potencies of
the ectoderm and of the endoderm, and we may add, of every elementary
organ in relation to every other, differ between themselves and also in
comparison with the blastoderm, from which they have originated. But the
diversity of the endoderm with respect to the ectoderm is not of the
same kind as its diversity in respect to the blastoderm. The potency
of the endoderm and that of the ectoderm are both specialised in their
typical manner, but compared with the potency of the blastoderm they
may be said not only to be specialised but also to be *restricted*: the
potency of the blastoderm embraces the whole, that of the so-called
germ-layer embraces only part of the whole; and this species of
restriction becomes clearer and clearer the further ontogeny advances:
at the end of it in the “ultimate elementary organs” there is no
prospective potency whatever.

A few new terms will serve to state a little more accurately what
happens. Of course, with regard to all morphogenesis which goes on
*immediately* from the blastoderm, the potency of the blastoderm is
restricted as much as are the potencies of the germ layers. We shall
call this sort of immediate potency *explicit*, and then we see at
once that, with regard to their explicit potencies, there are only
differences among the prospective potencies of the elementary organs;
but with respect to the *implicit* potency of any of these organs, that
is with respect to their potency as embracing the faculties of all their
derivations, there are also not only differences but true morphogenetic
restrictions lying at the very foundations of all embryology.

But now those of you who are familiar with morphogenetic facts will
object to me, that what we have stated about all sorts of restrictions
in ontogeny is not true, and you will censure me for having overlooked
regeneration, adventitious budding, and so on. To some extent the
criticism would be right, but I am not going to recant; I shall only
introduce another new concept. We are dealing only with *primary*
potencies in our present considerations, *i.e.* with potencies which
lie at the root of true embryology, not with those serving to regulate
disturbances of the organisation. It is true, we have in some way
disturbed the development of our sea-urchin’s egg in order to study
it; more than that, it would have been impossible to study it at all
without some sort of disturbance, without some sort of operation.
But, nevertheless, no potencies of what may properly be called the
*secondary* or restitutive type have been aroused by our operations;
nothing happened except on the usual lines of organogenesis. It is
true, some sort of regulation occurred, but that is included among the
factors of ontogeny proper.

We shall afterwards study more fully and from a more general point of
view this very important feature of “primary regulation” in its contrast
to “secondary regulation” phenomena. At present it must be enough to
say that in speaking of the restriction of the implicit potencies in
form-building we refer only to potencies of the primary type, which
contain within themselves some properties of a (primary) regulative
character.

*The Morphogenetic Function of Maturation in the Light of Recent
Discoveries*

Turning again to more concrete matters, we shall first try, with the
knowledge acquired of the potencies of the blastoderm and the so-called
germ layers of Echinus, to understand certain rather complicated
results which the experimental morphogenetic study of other animal
forms has taught us. We know from our historical sketch that there are
some very important aberrations from the type, to which the Echinus
germ belongs,[27] *i.e.* the type with an equal distribution of the
potencies over all the blastomeres. We know not only that in cases where
a regulation of the intimate structure of the protoplasm fails to occur
a partial development of isolated cells will take place, but that there
may even be a typical disposition of typical cells for the formation of
typical organs only, without any regulability.

[27] The reader will remember (see page 65, note 1), that even the germ
of Echinus is not quite equipotential along its main axis, but it is
equipotential in the strictest sense around this axis. The germs of
certain medusae seem to be equipotential in every respect, even in their
cleavage stages.

Let us first consider the last case, of which the egg of mollusca is a
good type: here there is no equal distribution of potencies whatever,
the cleavage-cells of this germ are a sort of real “mosaic” with regard
to their morphogenetic potentialities. Is this difference between the
germ of the echinoderms and the molluscs to remain where it is, and
not to be elucidated any further? Then there would be rather important
differences among the germs of different animals, at least with regard
to the degree of the specification of their cleavage cells, or if we
ascribe differences among the blastomeres to the organisation of the
fertilised egg ready for cleavage, there would be differences in the
morphogenetic organisation of the egg-protoplasm: some eggs would be
more typically specialised at the very beginning of morphogenesis than
others.

In the first years of the study of “Entwickelungsmechanik” I pointed out
that it must never be forgotten that the egg itself is the result of
organogenesis. If, therefore, there are real mosaic-like specifications
in some eggs at the beginning of cleavage, or during it, there may
perhaps have been an *earlier* stage in the individual history of
the egg which did not show such specifications of the morphogenetic
structure. Two American authors share the merit of having proved
this hypothesis. Conklin showed, several years ago, that certain
intracellular migrations and rearrangements of material do happen in
the first stages of ovogenesis in certain cases, but it is to E. B.
Wilson[28] that science owes a proper and definitive elucidation of the
whole subject. Wilson’s researches, pursued not only by descriptive
methods,[29] but also by means of analytical experiment, led him to the
highly important discovery that the eggs of several forms (nemertines,
molluscs), which after maturation show the mosaic type of specification
in their protoplasm to a more or less high degree, fail to show any
kind of specification in the distribution of their potencies before
maturation has occurred. In the mollusc egg a certain degree of
specification is shown already before maturation, but nothing to be
compared with what happens afterwards; in the egg of nemertines there is
no specification at all in the unripe egg.

[28] *Journ. Exp. Zool.* 1, 1904.

[29] Great caution must be taken in attributing any specific
morphogenetic part to differently coloured or constructed materials,
which may be observed in the egg-protoplasm in certain cases. They may
play such a part, but in other cases they certainly do not (see Lyon,
*Arch. Entw. Mech.* 23, 1907). The final decision always depends on
experiment.

Maturation thus becomes a part of ontogeny itself; it is not with
fertilisation that morphogenesis begins, there is a sort of ontogeny
anterior to fertilisation.

These words constitute a summary of Wilson’s researches. Taken together
with the general results obtained about the potencies of the blastula
and the gastrula of Echinus, they reduce what appeared to be differences
of degree or even of kind in the specification of the egg-protoplasm *to
mere differences in the time of the beginning of real morphogenesis*.
What occurs in some eggs, as in those of Echinus, at the time of the
definite formation of the germ layers, leading to a specification and
restriction of their prospective potencies, may happen very much earlier
in other eggs. But there exists in *every* sort of egg an *earliest*
stage, in which all parts of its protoplasm are equal as to their
prospectivity, and in which there are no potential diversities or
restrictions of any kind.

So much for differences in the *real material* organisation of the germ
and their bearing on inequipotentialities of the cleavage cells.

*The Intimate Structure of Protoplasm: Further Remarks*

Where a typical half- or quarter-development from isolated blastomeres
happens to occur, we know already that the impossibility of a regulation
of the *intimate polar-bilateral* structure may account for it. As this
impossibility of regulation probably rests on rather simple physical
conditions[30] it may properly be stated that equal distribution of
potencies is not wanting but is only overshadowed here. In this respect
there exists a logical difference of fundamental importance between
those cases of so-called “partial” or better, “fragmental” development
of isolated blastomeres in which a certain embryonic organ is wanting
on account of its specific morphogenetic material being absent, and
those cases in which the “fragmental” embryo lacks complete “halves” or
“quarters” with regard to general symmetry on account of the symmetry
of its intimate structure being irregularly disturbed. This logical
difference has not always received the attention which it undoubtedly
deserves. Our hypothetical intimate structure in itself is, of course,
also a result of factors concerned in ovogenesis. Only in one case do
we actually know anything about its origin: Roux has shown that in the
frog it is the accidental path of the fertilising spermatozoon in the
egg which, together with the polar axis, normally determines the plane
of bilateral symmetry; but this symmetry may be overcome and replaced
by another, if gravity is forced to act in an abnormal manner upon the
protoplasm; the latter showing parts of different specific gravity in
the eggs of all Amphibia.

[30] It seems that these physical conditions also--besides the real
specifications in the organisation of the egg--may be different before
and after maturation or (in other cases) fertilisation. (See Driesch,
*Archiv f. Entwickelungsmechanik*, 7, p. 98; and Brachet, *ibid.* 22, p.
325.)

*The Neutrality of the Concept of “Potency”*

Now we may close our rather long chapter on the distribution of
potencies in the germ; it has been made long, because it will prove to
be very important for further analytical discussion; and its importance,
in great measure, is due to its freedom from prepossessions. Indeed,
the concept of prospective potency does not prejudice anything; we
have said, it is true, that limitations of potencies may be due to
the presence of specific parts of organisation in some cases; that,
at least, they may be connected therewith; but we have not determined
at all what a prospective potency really is, what the term really is
to signify. It may seem that such a state of things gives an air of
emptiness to our discussions, that it leaves uncertain what is the most
important. But, I think, our way of argument, which tries to reach the
problems of greatest importance by degrees, though it may be slow, could
hardly be called wrong and misleading.

β. THE “MEANS” OF MORPHOGENESIS

We now proceed to an analysis of what may properly be called the *means*
of morphogenesis, the word “means” being preferable to the more usual
one “conditions” in this connection, as the latter would not cover the
whole field. It is in quite an unpretentious and merely descriptive
sense that the expression “means” should be understood at present; what
is usually called “conditions” is part of the morphogenetic means in our
sense.

β′. *The Internal Elementary Means of Morphogenesis*

We know that all morphogenesis, typical or atypical, primary or
secondary, goes on by one morphogenetic elementary process following the
other. Now the very foundation of these elementary processes themselves
lies in the elementary functions of the organism as far as they result
in the formation of stable visible products. Therefore the elementary
functions of the organism may properly be called the internal “means” of
morphogenesis.

Secretion and migration are among such functions; the former happening
by the aid of chemical change or by physical separation, the latter by
the aid of changes in surface tension. But hardly anything more concrete
has been made out about these or similar points at present.

We therefore make no claim to offer a complete system of the internal
elementary means of morphogenesis. We shall only select from the whole
a few topics of remarkable morphogenetic interest, and say a few words
about each.

But, first of all, let us observe that the elementary means of
morphogenesis are far from being morphogenesis themselves. The word
“means” itself implies as much. It would be possible to understand each
of these single acts in morphogenesis as well as anything, and yet to be
as far from understanding the whole as ever. All means of morphogenesis
are only to be considered as the most general frame of events within
which morphogenesis occurs.

*Some Remarks on the Importance of Surface Tension in
Morphogenesis.*--There are a few purely physical phenomena which have
a special importance in organic morphology, all of them connected
with capillarity or surface tension. Soap-lather is a very familiar
thing to all of you: you know that the soap-solution is arranged here
in very thin planes separated by spaces containing air: it was first
proved by Berthold[31] that the arrangement of cells in organic tissues
follows the same type as does the arrangement of the single bubbles of
a soap-lather, and Bütschli[32] added to this the discovery that the
minute structure of the protoplasm itself is that of a foam also. Of
course it is not one fluid and one gas which make up the constituents
of the structure in the organisms, as is the case in the well-known
inorganic foams, but two fluids, which do not mix with one another. One
general law holds for all arrangements of this kind: the so-called law
of least surfaces, expressed by the words that the sum of all surfaces
existing is a minimum; and it again is a consequence of this law, if
discussed mathematically, that four lines will always meet in one point
and three planes in one line. This feature, together with a certain law
about the relation of the angles meeting in one line to the size of the
bubbles, is realised most clearly in many structures of organic tissues,
and makes it highly probable, at least in some cases, that capillarity
is at work here. In other cases, as for instance in many plants, a kind
of outside pressure, the so-called tissue tension, may account for the
arrangement in surfaces *minimae areae*. Cleavage stages are perhaps
the very best type in which our physical law is expressed: and here
it may be said to have quite a simple application whenever all of the
blastomeres are of the same physical kind, whilst some complications
appear in germs with a specialised organisation and, therefore,
with differences in the protoplasm of their single blastomeres. In
such instances we may say that the physical law holds as far as the
conditions of the system permit, these conditions ordinarily consisting
in a sort of non-homogeneity of the surfaces.

[31] *Studien über Protoplasmamechanik*, Leipzig, 1886.

[32] *Unters. üb. mikroskopische Schäume und das Protoplasma*, Leipzig,
1892.

It seems, from the researches of Dreyer,[33] that the formation of
organic skeletons may also be governed by the physically conditioned
arrangement of protoplasmatic or cellular elements, and some phenomena
of migration and rearrangement among cleavage cells, as described by
Roux, probably also belong here.

[33] *Jena. Zeitschr.* 26, 1892.

But let us never forget that the laws of surface tension only give
us the most general type of an arrangement of elements in all these
cases, nothing else. A physical law never accounts for the Specific!
Capillarity gives us not the least clue to it. As the organic substance,
at least in many cases, is a fluid, it must of course follow the general
laws of hydrostatics and hydrodynamics, but life itself is as little
touched by its fluid-like or foam-like properties as it is by the fact
that living bodies have a certain weight and mass.

All indeed that has been described may be said to belong, in the
broadest meaning of the word, to what is called by Roux “correlation of
masses,” though this author originally intended to express by this term
only some sorts of passive pressure and deformation amongst embryonic
parts as discovered especially by His.

We must be cautious in admitting that any organic feature has been
explained, even in the most general way, by the action of physical
forces. What at first seems to be the result of mechanical pressure may
afterwards be found to be an active process of growth, and what at first
seems to be a full effect of capillarity among homogeneous elements may
afterwards be shown to depend on specialised metabolic conditions of the
surfaces as its principal cause.[34]

[34] According to Zur Strassen’s results the early embryology of
*Ascaris* proceeds almost exclusively by cellular surface-changes: the
most typical morphogenetic processes are carried out by the aid of this
“means.” As a whole, the embryology of *Ascaris* stands quite apart and
presents a great number of unsolved problems; unfortunately, the germ of
this form has not been accessible to experiment hitherto.

There are other physical phenomena too, which assist morphogenesis;
osmotic pressure for instance, which is also well known to operate in
many purely physiological processes. But all these processes are only
means of the organism, and can never do more than furnish the general
type of events. They do not constitute life; they are *used* by life;
let it remain an open question, for the present, how the phenomenon of
“life” is to be regarded in general.[35]

[35] Rhumbler has recently published a general survey of all attempts to
“explain” life, and morphogenesis in particular, in a physico-chemical
way (“Aus dem Lückengebiet zwischen organismischer und anorganismischer
Natur,” *Ergeb. Anat. u. Entw.-gesch.* 15, 1906). This *very
pessimistic* survey is the more valuable as it is written by a convinced
“mechanist.”

*On Growth*.--Among the internal morphogenetical means which are of
a so-called physiological character, that is, which nobody claims to
understand physically at present, there is in the first place *growth*,
which must be regarded as a very essential one.

Analytically we must carefully discriminate between the increase in the
size of the cavities of an organism by a passive extension of their
surfaces and the proper growth of the individual cells, which again
may be due either to mere extension or to real assimilation. Osmotic
pressure, of course, plays an important part both in the growth of the
body-cavities and in simple cellular extension. We repeat the caution
against believing too much to be explained by this phenomenon: it is the
organism which by the secretion of osmotic substances in the cavities or
the protoplasm of the cells prepares the ground for growth even of this
osmotic sort. The real cellular growth which proceeds on the basis of
assimilation cannot, of course, be accounted for by osmotic events, not
even in its most general type.

Ontogenetical growth generally sets in, both in animals and in plants,
after the chief lines of organisation are laid out; it is only the
formation of the definite histological structures which usually runs
parallel to it.

*On Cell-division.*--We have already said a good deal about the
importance of cell-division in ontogeny: it accompanies very many of the
processes of organisation in all living beings. But even then, there are
the Protozoa, in the morphogenesis of which it does not occur at all,
and there have also become known many cases of morphogenesis in higher
animals, mostly of the type of regulation, in which cellular division
is almost or wholly wanting. Therefore, cellular division cannot be
the true reason of differentiation, but is only a process, which
though necessary in some cases, cannot be essential to it. It must be
conceded, I believe, that the same conclusion can be drawn from all our
experiments on very young stages of the germ.

The investigations of the last few years have made it quite clear that
even in organisms with a high power of morphogenetic regulation it is
always the form of the whole, but not the individual cell, which is
subjected to the regulation processes. Starting from certain results
obtained by T. H. Morgan, I was able to show that in all the small but
whole larvae, reared from isolated blastomeres, the size of the cells
remains normal, only their number being reduced; and Boveri has shown
most clearly that it is always the size of the nucleus--more correctly,
the mass of the chromatin--which determines how large a cell of a
certain histological kind is to be. In this view, the cell appears even
more as a sort of material used by the organism as supplied, just as
workmen can build the most different buildings with stones of a given
size.

β″. *The External Means of Morphogenesis*

We now know what internal means of morphogenesis are, and so we may
glance at some of the most important “outer means” or “conditions” of
organisation.

Like the adult, the germ also requires a certain amount of heat, oxygen,
and, when it grows up in the sea, salinity in the medium. For the germ,
as for the adult, there exists not only a minimum but also a maximum
limit of all the necessary factors of the medium; the same factor which
at a certain intensity promotes development, disturbs it from a certain
other intensity upwards.

Within the limits of this minimum and this maximum of every outside
agent there generally is an increase in the rate of development
corresponding to the increase of intensity of the agent. The
acceleration of development by heat has been shown to follow the law of
the acceleration of chemical processes by a rise of temperature; that
seems to prove that certain chemical processes go on during the course
of morphogenesis.

Almost all that has been investigated of the part played by the external
conditions of development has little bearing on specific morphogenesis
proper, and therefore may be left out of account here: we must, however,
lay great stress on the general fact that there *is* a very close
dependence of morphogenesis on the outside factors, lest we should be
accused afterwards of having overlooked it.

Of course all “external” means or conditions of morphogenesis can
actually relate to morphogenetic processes only by becoming in some way
“internal,” but we unfortunately have no knowledge whatever how this
happens. We at present are only able to ascertain what must necessarily
be accomplished in the medium, in order that normal morphogenesis may go
on, and we can only suppose that there exist certain specific internal
general states, indispensable for organogenesis but inaccessible to
present modes of investigation.[36]

[36] Compare the analytical discussions of Klebs, to whom we owe a great
series of important discoveries in the field of morphogenetic “means”
in botany. (*Willkürliche Entwickelungsänderungen bei Pflanzen*, Jena,
1903; see also *Biol. Centralblatt*, vol. xxiv., 1904, and my reply to
Klebs, *ibid.* 23, 1903.)

*The Discoveries of Herbst.*--There are but few points in the doctrine
of the external means or conditions of organogenesis which have a
more special bearing on the specification of proper form, and which
therefore require to be described here a little more fully. All
these researches, which have been carried out almost exclusively by
Herbst,[37] relate to the effect of the chemical components of sea-water
upon the development of the sea-urchin. If we select the most important
of Herbst’s results, we must in the first place say a few words on
the part taken by lime or calcium, not only in establishing specific
features of form, but in rendering individual morphogenesis possible at
all. Herbst has found that in sea-water which is deprived of calcium the
cleavage cells and many tissue cells also completely lose contact with
each other: cleavage goes on quite well, but after each single division
the elements are separated; at the end of the process you find the 808
cells of the germ together at the bottom of the dish, all swimming about
like infusoria. There seems to be some influence of the calcium salts
upon the physical state of the surfaces of the blastomeres.

[37] *Arch. Entw. Mech.* 17, 1904.

It is not without interest to note that this discovery has an important
bearing on the technical side of all experiments dealing with the
isolation of blastomeres. Since the separation of the single cleavage
elements ceases as soon as the germs are brought back from the mixture
without lime into normal sea-water, it of course is possible to separate
them up to any stage which it is desired to study, and to keep them
together afterwards. Thus, if for instance you want to study the
development of isolated cells of the eight-cell stage, you will leave
the egg in the artificial mixture containing no calcium until the
third cleavage, which leads from the four- to the eight-cell stage, is
finished. The single eight cells brought back to normal sea-water at
this point will give you the eight embryos you want. All researches
upon the development of isolated blastomeres since the time of Herbst’s
discovery have been carried out by this method, and it would have been
quite impossible by the old method of shaking to pursue the study into
such minute detail as actually has been done. It may be added that
calcium, besides its cell-uniting action, is also of primary importance
in the formation of the skeleton.

Among all the other very numerous studies of Herbst we need only mention
that potassium is necessary for the typical growth of the intestine,
just as this element has been found necessary for normal growth in
plants, and that there must be the ion SO_4, or in other terms,
sulphur salts present in the water, in order that the germs may acquire
their pigments and their bilateral symmetry. This is indeed a very
important result, though it cannot be said to be properly understood. It
is a fact that in water without sulphates the larvae of Echinus retain
the radial symmetry they have had in the very earliest stages, and may
even preserve that symmetry on being brought back to normal sea-water if
they have spent about twenty-four hours in the artificial mixture.

We may now leave the subject of Herbst’s attempts to discover the
morphogenetic function of the single constituents of normal sea-water,
and may devote a few words to the other branch of his investigations,
those dealing with the morphogenetic effects of substances which are not
present in the water of the sea, but have been added to it artificially.
Here, among many other achievements, Herbst has made the most
important discovery that all salts of lithium effect radical changes
in development.[38] I cannot describe fully here how the so-called
“lithium larva” originates; let me only mention that its endoderm is
formed outside instead of inside, that it is far too large, that there
is a spherical mass between the ectodermal and the endodermal part of
the germ, that a radial symmetry is established in place of the normal
bilateralism, that no skeleton exists, and that the mesenchyme cells
are placed in a quite abnormal position. All these features, though
abnormal, are typical of the development in lithium. The larvae present
no really pathological appearance at all, and, therefore, it may indeed
be said that lithium salts are able to change fundamentally the whole
course of morphogenesis. It detracts nothing from the importance of
these discoveries that, at present, they stand quite isolated: only with
lithium salts has Herbst obtained such strange results, and only upon
the eggs of echinids, not even upon those of asterids, do lithium salts
act in this way.

[38] *Zeitschr. wiss. Zool.* 55, 1902; and *Mitt. Neapel.* 11, 1903.

γ. THE FORMATIVE CAUSES OR STIMULI

*The Definition of Cause*

We cannot begin the study of the “causes” of the differentiation of
form without a few words of explanation about the terminology which we
shall apply. Causality is the most disputed of all categories; many
modern scientists, particularly in physics, try to avoid the concept of
cause altogether, and to replace it by mere functional dependence in
the mathematical meaning of the term. They claim to express completely
by an equation all that is discoverable about any sort of phenomena
constantly connected.

I cannot convince myself that such a very restricted view is the right
one: it is very cautious, no doubt, but it is incomplete, for we *have*
the concept of the acting “cause” in our Ego and are *forced* to search
for applications of it in Nature. On the other hand, it does not at all
escape me that there are many difficulties, or rather ambiguities, in
applying it.

We may call the “cause” of any event, the sum total of all the
constellations of facts which must be completed in order that the event
may occur; it is in this meaning, for instance, that the first principle
of energetics applies the term in the words *causa aequat effectum*.
But, by using the word only in this very general sense, we deprive
ourselves of many conveniences in the further and more particular study
of Nature. Would it be better to say that the “cause” of any event is
the very last change which, after all the constellations necessary for
its start are accomplished, must still take place in order that the
event may actually occur? Let us see what would follow from such a use
of the word causality. We here have an animal germ in a certain stage,
say a larva of Echinus, which is just about to form the intestine; all
the internal conditions are fulfilled, and there is also a certain
temperature, a certain salinity, and so on, but there is no oxygen in
the water: the intestine; of course, will not grow in such a state of
things, but it soon will when oxygen is allowed to enter the dish.
Is, therefore, oxygen the cause of the formation of the intestine of
echinus? Nobody, I think, would care to say so. By such reasoning,
indeed, the temperature, or sodium, might be called the “cause” of
any special process of morphogenesis. It, therefore, seems to be of
little use to give the name of cause to that factor of any necessary
constellation of events which accidentally happens to be the last that
is realised. But what is to be done then?

Might we not say that the cause of any morphogenetic process is that
typical property, or quality, or change, on which its specific character
depends, on which depends for example, the fact that now it is the
intestine which appears, while at another time it is the lens of the
eye? We might very well, but we already have our term for this sort
of cause, which is nothing else than our prospective potency applied
to that elementary organ from which the new process takes its origin.
The prospective potency indeed is the truly immanent cause of every
specification affecting single organogenetic processes. But we want
something more than this.

We may find what we want by considering that each single elementary
process or development not only has its specification, but also has
its specific and typical place in the whole--its locality. Therefore
we shall call the “cause” of a single morphogenetic process, that
occurrence on which depends its *localisation*, whether its specific
character also partly depends on this “cause” or not.[39]

[39] In certain cases part of the specific feature of the process in
question may also depend on the “cause” which is localising it, *e.g.*
in the galls of plants.

This definition of “cause” in morphology may be artificial; in any
case it is clear. And at the same time the concepts of the prospective
potency and of the “means” of organogenesis now acquire a clear and
definite meaning: potency is the real basis of the specific character
of every act in morphogenesis, and “means,” including conditions, are
the sum of all external and internal general circumstances which must be
present in order that morphogenetic processes may go on, without being
responsible for their specificity or localisation.

It is implied in these definitions of cause and potency, that the former
almost always will be of that general type which usually is called a
stimulus or “Auslösung,” to use the untranslatable German word. There is
no quantitative correspondence between our “cause” and the morphogenetic
effect.

*Some Instances of Formative and Directive Stimuli*

Again it is to Herbst that we owe not only a very thorough logical
analysis of what he calls “formative and directive stimuli”[40] but also
some important discoveries on this subject. We cannot do more here than
barely mention some of the most characteristic facts.

[40] Herbst, “Ueber die Bedeutung die Reizphysiologie für die kausale
Auffassung von Vorgängen in der tierischen Ontogenese” (*Biol.
Centralblatt*, vols. xiv., 1894, and xv., 1895); *Formative Reize in der
tierischen Ontogenese*, Leipzig, 1901. These important papers must be
studied by every one who wishes to become familiar with the subject. The
present state of science is reviewed in my articles in the *Ergebnisse
der Anatomie und Entwickelungsgeschichte*, vols. xi. and xiv., 1902 and
1905.

Amongst plants it has long been known that the direction of light or of
gravity may determine where roots or branches or other morphogenetic
formations are to arise; in hydroids also we know that these factors
of the medium may be at work[41] as morphogenetic causes, though most
of the typical architecture of hydroid colonies certainly is due to
internal causes, as is also much of the organisation in plants.

[41] Compare the important papers by J. Loeb, *Untersuchungen zur
physiologischen Morphologie der Tiere*, Würzburg, 1891-2.

Light and gravity are external formative causes; beside that they are
merely “localisers.” But there also are some external formative stimuli,
on which depends not only the place of the effect, but also part of its
specification. The galls of plants are the most typical organogenetic
results of such stimuli. The potencies of the plant and the specific
kind of the stimulus equally contribute to their specification; for
several kinds of galls may originate on one sort of leaves.

Scarcely any exterior formative stimuli are responsible for animal
organisation; and one would hardly be wrong in saying that this
morphogenetic independence in animals is due to their comparatively
far-reaching functional independence of those external agents which
have any sort of direction. But many organogenetic relations are known
to exist between the single parts of animal germs, each of these parts
being in some respect external to every other; and, indeed, it might
have been expected already *a priori*, that such formative relations
between the parts of an animal embryo must exist, after all we have
learned about the chief lines of early embryology. If differentiation
does not go on after the scheme of Weismann, that is, if it is not
carried out by true “evolutio” from within, how could it be effected
except from without? Indeed, every embryonic part may in some respect be
a possible cause for morphogenetic events, which are to occur on every
other part: it is here that the very roots of epigenesis are to be found.

Heliotropism and geotropism are among the well-known physiological
functions of plants: the roots are seen to bend away from the light and
towards the ground; the branches behave just in the opposite way. It now
has been supposed by Herbst that such “directive stimuli” may also be
at work among the growing or wandering parts of the embryo, that their
growth or their migration may be determined by the typical character of
other parts, and that real morphogenetic characters can be the result of
some such relation; a sort of “chemotropism” or “chemotaxis” may be at
work here. Herbst himself has discussed theoretically several cases of
organogenesis in which the action of directive stimuli is very probable.
What has become actually known by experiment is not very much at
present: the mesenchyme cells of Echinus are directed in their migration
by specified places in the ectoderm, the pigment cells of the yolk-sac
of the fish fundulus are attracted by its blood vessels, and nerves
may be forced to turn into little tubes containing brain substance;
but of course only the first two instances have any bearing on typical
morphogenesis.

The first case of an “internal formative stimulus” in the proper sense,
that is, of one embryonic part causing another to appear, was discovered
by Herbst himself. The arms of the so-called pluteus of the sea-urchin
are in formative dependence on the skeleton--no skeleton, no arms; so
many skeleton primordia,[42] in abnormal cases, so many arms; abnormal
position of the skeleton, abnormal position of the arms: these three
experimental observations form the proof of this morphogenetic relation.

[42] I use the word “primordia” for the German “Anlage”; it is better
than the word “rudiment,” as the latter may also serve to signify
the very last stage of a certain formation that is disappearing
(phylogenetically).

It may be simple mechanical contact, or it may be some chemical
influence that really constitutes the “stimulus” in this case;
certainly, there exists a close and very specific relation of the
localisation of one part of the embryo to another. Things are much the
same in another case, which, after having been hypothetically stated
by Herbst on the basis of pathological data, was proved experimentally
by Spemann. The lens of the eye of certain Amphibia is formed of their
skin in response to a formative stimulus proceeding from the so-called
primary optic vesicle. If this vesicle fails to touch the skin, no lens
appears; and, on the other hand, the lens may appear in quite abnormal
parts of the skin if they come into contact with the optic vesicle after
transplantation.

But formative dependence of parts may also be of different types.

We owe to Herbst the important discovery that the eyes of crayfishes,
after being cut off, will be regenerated in the proper way, if the optic
ganglion is present, but that an antenna will arise in their place
if this ganglion has also been removed. There must in this case be
some unknown influence of the formative kind on which depends, if not
regeneration itself, at least its special character.

In other cases there seems to be an influence of the central nervous
system on the regenerative power in general. Amphibia, for instance,
are said to regenerate neither their legs (Wolff), nor their tail
(Godlewski), if the nervous communications have been disturbed. But
in other animals there is no such influence; and in yet others, as
for instance, in Planarians, it must seem doubtful at present whether
the morphogenetic influence of the nervous system upon processes of
restoration is more than indirect; the movements of the animal, which
become very much reduced by the extirpation of the ganglia, being one of
the main conditions of a good regeneration.

Of course, all we have said about the importance of special materials
in the ripe germ, as bearing on specifically localised organisations,
might be discussed again in our present chapter, and our intimate
polar-bilateral structure of germs may also be regarded as embracing
formative stimuli, at any rate as far as the actual poles of this
structure are concerned. This again would bring us to the problem of
so-called “polarity” in general, and to the “inversion” of polarity,
that is to a phenomenon well known in plants and in many hydroids and
worms, viz., that morphogenetic processes, especially of the type of
restitutions, occur differently, according as their point of origin
represents, so to speak, the positive or the negative, the terminal or
the basal end of an axis, but that under certain conditions the reverse
may also be the case. But a fuller discussion of these important facts
would lead us deeper and deeper into the science of morphogenesis
proper, without being of much use for our future considerations.

And so we may close this section[43] on formative stimuli or “causes”
of morphogenesis by shortly adding, more on account of its factual
than of its logical interest, that the phenomenon of the determination
of sex,[44] according to the latest researches, seems to depend on
cytological events occurring in the very earliest embryonic stages,
say even before ontogeny, and not on formative stimuli proper[45]: it
seems, indeed, as if the sexual products themselves would account for
the sex of the individual produced by them, particularly if there were
differences in their chromatin.[46]

[43] A full analysis of the subject would not only have to deal with
formative stimuli as inaugurating morphogenetic processes, but also with
those stimuli which terminate or stop the single acts of morphogenesis.
But little is actually known about this topic, and therefore the reader
must refer to my other publications. I will only say here, that the end
of each single morphogenetic act may either be determined at the very
beginning or occur as an actual stopping of a process which otherwise
would go on for ever and ever; in the first case some terminating
factors are included in the very nature of the morphogenetic act itself.

[44] A full account of the present state of the subject will be found in
Morgan’s *Experimental Zoology*, New York, 1907.

[45] But there certainly exist many formative relations between the real
sexual organs and the so-called secondary sexual characters. Herbst has
given a full analytical discussion of all that is known on this subject;
but the facts are much more complicated than is generally supposed, and
do not lend themselves therefore to short description. See also Foges,
*Pflüger’s Arch.* 93, 1902.

[46] It seems that in some cases (*Dinophilus*, certain Arthropods)
the sexual products are invariably determined as “arrenogennetic”
or as “thelygennetic” (Wilson, *Journ. Exp. Zool.* ii. and iii.
1905-6), whilst in others (Amphibia) the state of maturation or
“super”-maturation determines the sex of the future organism (R.
Hertwig, *Verh. D. Zool. Ges.* 1905-7).

δ. THE MORPHOGENETIC HARMONIES

Let us now turn again to considerations of a more abstract kind: we have
become acquainted with some morphogenetic interactions among the parts
of a developing embryo; and, indeed, we can be sure that there exist far
more of such interactions than we know at present.

But it is far from being true that the development of each embryonic
part depends on the existence or development of every other one.

On the contrary, it is a very important and fundamental feature
of organogenesis that it occurs in separate lines, that is to
say, in lines of processes which may start from a common root, but
which are absolutely independent of one another in their manner of
differentiation. Roux has coined the term “self-differentiation” to
denote this phenomenon, and we admit that this term may be conveniently
used for the purpose, if only it can be kept in mind that its sense is
always relative, and that it is also negative. Suppose a part, *A*,
shows the phenomenon of self-differentiation: this means that the
further development of *A* is not dependent on certain other parts,
*B*, *C*, and *D*; it does *not* mean at all that *A* has not been
formatively dependent on some other parts, *E* or *F* at the time of
its first appearance, nor does it imply that there might not be many
formative actions among the constituents of *A* itself.

We indeed are entitled to say that the ectoderm of Echinus shows
“self-differentiation” with regard to the endoderm; it acquires its
mouth, for instance, as has been shown by experiment, even in cases
where no intestine is present at all (Fig. 10); but ectoderm and
endoderm both are formatively dependent on the intimate and the material
organisation of the blastoderm. It further seems from the most recent
experiments that the nerves and the muscles of the vertebrates are
independent of each other in their differentiation, but that their fate
is probably determined by formative processes in the very earliest
stages of ontogeny.

[Illustration: Fig. 10.--Pluteus-larva of Sphaerechinus.

The Intestine (i) is developed outside instead of inside (by means of
raising the temperature); but the mouth (r) is formed in its normal
place. S = Skeleton.]

The phenomenon of self-differentiation, properly understood, now may
help to the discovery of one most general character of all development.
If the phenomenon of self-differentiation really occurs in ontogeny
in its most different aspects, and if, on the other hand, in spite
of this relative morphogenetic independence of embryonic parts, the
resulting organism is one whole in organisation and in function, some
sort of *harmony of constellation*, as it may properly be styled, must
be said to be one of the most fundamental characters of all production
of individual form. In establishing this harmony we do nothing more
than describe exactly what happens: the harmony is shown by the fact
that there is a whole organism at the end, in spite of the relative
independence of the single events leading to it.

But still another sort of harmony is revealed in morphogenesis, by an
analysis of the general conditions of the formative actions themselves.
In order that these actions may go on properly the possibility must be
guaranteed that the formative causes may always find something upon
which to act, and that those parts which contain the potencies for the
next ontogenetic stage may properly receive the stimuli awaking these
potencies: otherwise there would be no typical production of form at
all. This, the second species of harmonious relations to be described in
ontogeny, may be called *causal harmony*; the term simply expresses the
unfailing relative condition of formative causes and cause-recipients.

Finally, in *functional harmony* we have an expression descriptive
of the unity of organic function, and so we may state, as the latest
result of our analytical theory of development up to this point, that
individual morphogenesis is marked by a *threefold harmony* among its
parts.

ε. ON RESTITUTIONS[47]

[47] Driesch, *Die organischen Regulationen*, Leipzig, 1901; Morgan,
*Regeneration*, New York, 1901.

At this stage we leave for a while our analytical studies of ontogeny
proper. We must not forget that typical ontogenesis is not the only form
in which morphogenesis can occur: the organic form is able to restore
disturbances of its organisation, and it certainly is to be regarded as
one of the chief problems of analytical morphogenesis to discover the
specific and real stimulus which calls forth the restoring processes.
For simply to say that the disturbance is the cause of the restoration
would be to evade the problem instead of attacking it. But there are
still some other problems peculiar to the doctrine of restitutions.

*A few Remarks on Secondary Potencies and on Secondary Morphogenetic
Regulations in General*

We have only briefly mentioned in a previous chapter that there
exist many kinds of potencies of what we call the secondary or truly
restitutive type, and that their distribution may be most various and
quite independent of all the potencies for the primary processes
of ontogeny proper. Let us first add a few words about the concept
of “secondary restitution” and about the distribution of secondary
potencies in general.

Primary ontogenetic processes founded upon primary potencies may *imply*
regulation, or more correctly, restitution in many cases: so it is,
when fragments of the blastula form the whole organism, or when the
mesenchyme cells of Echinus reach their normal final position by an
attraction on the part of specific localities of the ectoderm in spite
of a very abnormal original position enforced upon them by experiment.
In these cases we speak of primary regulations or restitutions;
disturbances are neutralised by the very nature of the process in
question. We speak of secondary restitution whenever a disturbance
of organisation is rectified by processes foreign to the realm of
normality; and these abnormal lines of events are revealed to us in the
first place by the activity of potencies which remain latent in ontogeny
proper.

We know already that a certain kind of secondary restitution has
been discovered lately, very contradictory to the theoretical views
of Weismann; the process of restoration being carried out not by any
definite part of the disturbed organisation, but by all the single
elements of it. The problem of the distribution of secondary potencies
in these cases of so-called “re-differentiation” is to form our special
study in the next chapter. In all other cases restoration processes
start from specific localities; if they occur on the site of the
wound which caused the disturbance, we speak of regeneration; if they
occur at some distance from the wound, we call them adventitious
processes. Besides these three types of processes of restitution there
may be mentioned a fourth one, consisting in what is generally called
compensatory hypertrophy; the most simple case of such a compensatory
process is when one of a pair of organs, say a kidney, becomes larger
after the other has been removed.[48] Finally, at least in plants, a
change of the directive irritability, of so-called “geotropism” for
instance, in certain parts may serve to restore other more important
parts.

[48] But real compensatory differentiation occurs in the cases of
so-called “hypertypy” as first discovered by Przibram and afterwards
studied by Zeleny: here the two organs of a pair show a different degree
of differentiation. Whenever the more specialised organ is removed the
less developed one assumes its form. Similar cases, which might simply
be called “compensatory heterotypy,” are known in plants, though only
relating to the actual fate of undifferentiated “Anlagen” in these
organisms. A leaf may be formed out of the Anlage of a scale, if all the
leaves are cut off, and so on.

In two of these general types of restitution, in regeneration proper and
in the production of adventitious organs, the potencies which underlie
these processes may be said to be “complex.” It is a complicated series
of events, a proper morphogenesis in itself, for which the potency
has to account, if, for instance, a worm newly forms its head by
regeneration, or if a plant restores a whole branch in the form of an
adventitious bud.

Such generalisations as are possible about the distribution of complex
potencies are reserved for a special part of our future discussion.

Secondary restitution is always, like ontogeny, a process of
morphogenesis, and therefore all the questions about single formative
stimuli, and about internal and external conditions or means, occur
again. But of course we cannot enter into these problems a second time,
and may only say that, especially in regeneration proper, the specific
type of the regenerative formation of any part may differ very much from
the ontogenetic type of its origin: the end of both is the same, but the
way can be even fundamentally different in every respect.

*The Stimuli of Restitutions*[49]

[49] For a fuller analysis compare my opening address delivered before
the section of “Experimental Zoology” at the Seventh Zoological
Congress, Boston, 1907: “The Stimuli of Restitutions” (see Proceedings
of that Congress).

But now we turn to the important question: what is the precise
stimulus[50] that calls forth processes of restitution; or, in other
words, what must have happened in order that restitution may occur?

[50] The problem of the stimulus of a secondary restitution as a
whole must not be confused with the very different question, what the
single “formative stimuli” concerned in the performance of a certain
restitutive act may be. With regard to restitution as a *whole* these
single “formative stimuli” might properly be said to belong to its
“internal means”--in the widest sense of the word.

That the operation in itself, by its removing of mechanical obstacles,
cannot be the true stimulus of any restitutions, is simply shown by all
those restitutions that do not happen at the place of the wound. If we
took a narrower point of view, and if we only considered regeneration
proper from the wound itself, we might probably at first be inclined to
advocate the doctrine that the removing of some obstacles might in fact
be the stimulus to the process of restoration; but, even then, why is
it that just what is wanted grows out? Why is there not only growth,
but specific growth, growth followed by specification? The removing
of an obstacle could hardly account for that. But, of course, taking
account of all the adventitious restitutions--that is, all restorations
not beginning at the wound itself--the theory that the removing of
obstacles is the stimulus to restoration becomes, as we have said, quite
impossible.[51]

[51] T. H. Morgan is very right in stating that, in regeneration, the
“obstacle” itself is newly formed by the mere process of healing,
previous to all restitution, and that true restitution happens all the
same.

But where then is the stimulus to be found? There is another rather
simple theory of the “Auslösung” of restitutions,[52] which starts
from the phenomena of compensatory hypertrophy and some occurrences
among plants. The removal of some parts of the organism, it is said,
will bring its other parts into better conditions of nutrition, and
therefore these parts, particularly if they are of the same kind, will
become larger. Granted for the moment that such a view may hold in cases
when one of a pair of glands becomes larger after the other has been
removed, or when pruning of almost all the leaves of a tree leads to the
rest becoming larger, it certainly must fail to explain the fact that
in other cases true *new* formations may arise in order to restore a
damaged part, or that the latter may be regenerated in its proper way.
For *merely quantitative* differences in the mixture of the blood or of
the nourishing sap in plants can never be a sufficient reason for the
highly typical and *qualitative* structure of newly-formed restitutions.
And even in the most simple cases of a mere increase in the size of
some parts, that is, in the simplest cases of so-called compensatory
hypertrophy,[53] it is at least doubtful, if not very improbable, that
the compensation is accomplished in such a purely passive way, because
we know that in other cases it is usually the growth of the young parts
that actively attracts the nourishment: there is first differentiation
and growth, and *afterwards* there is a change in the direction of the
nourishing fluids.

[52] I merely mention here the still “simpler” one--applicable of course
to regeneration proper exclusively--that for the simple reason of being
“wounded,” *i.e.* being a surface open to the medium, the “wound” brings
forth all that is necessary to complete the organism.

[53] That compensatory hypertrophy cannot be due to “functional
adaptation”--to be analysed later on--was proved by an experiment of
Ribbert’s. Compensation may occur before the function has made its
appearance, as was shown to be the case in the testicles and mammae of
rabbits. (*Arch. Entw. Mech.* 1, 1894, p. 69.)

The process of true regeneration, beginning at the locality of the wound
itself, has been shown by Morgan, even as regards its rate, to occur
quite irrespectively of the animal being fed or not.[54] There could
hardly be a better demonstration of the fundamental fact that food
assists restitution, but does not “cause” it in any way.

[54] At any given time only the absolute size of the regenerated part is
greater in animals which are well fed; the degree of differentiation is
the same in all. Zeleny has found that, if all five arms of a starfish
are removed, each one of them will regenerate more material in a given
time than it would have done if it alone had been removed. But these
differences also only relate to absolute size and not to the degree
of differentiation. They possibly may be due in fact to conditions of
nourishment, but even here other explanations seems possible (Zeleny,
*Journ. exp. Zool.* 2, 1905).

But in spite of all we have said, there seems to be some truth in
regarding the nutritive juices of animals and plants as somehow
connected with the stimulus of restitutions: only in this very cautious
form, however, may we make the hypothesis. It has been shown for both
animals and plants, that morphogenesis of the restitutive type may be
called forth even if the parts, now to be “regenerated” have not been
actually removed; *e.g.* in the so-called super-regeneration of legs
and tails in Amphibia, of the head in Planarians, of the root-tip in
plants and in some other cases. Here it has always been a disturbance
of the normal connection of some parts with the rest of the organism
which proved to be the reason of the new formation. This shows that
something to do with the communication among parts is at least connected
with restitution, and this communication may go on either by the unknown
action of specific tissues or by the aid of the blood or sap.[55] But
in what this change or break of specific communication consists, is
absolutely unknown. One might suppose that each part of the organisation
constantly adds some sort of ferment to the body fluids outside or
inside the cells, that the removing of any part will change the
composition of these fluids in this particular respect, and that this
change acts as a sort of communication to summon the restituting parts
of the whole to do their duty.[56]

[55] For a good discussion of “super-regeneration” in the roots of
plants see Němec, *Studien über die Regeneration*, Berlin, 1905. Goebel
and Winkler have succeeded in provoking the “restitution” of parts which
were not removed at all by simply stopping their functions (leaves of
certain plants were covered with plaster, etc.). (*Biol. Centralbl.* 22,
1902, p. 385; *Ber. Bot. Ges.* 20, 1902, p. 81.) A fine experiment is
due to Miehe. The alga *Cladophora* was subjected to “plasmolysis,” each
cell then formed a new membrane of its own around the smaller volume of
its protoplasm; after that the plants were brought back to a medium of
normal osmotic pressure, and then each single cell grew up into a little
plant (all of them being of the same polarity!). Two questions seem
to be answered by this fact: loss of communication is of fundamental
importance to restitution, and the removal of mechanical obstacles plays
no part in it, for the mechanical resistances were the same at the end
of the experiment as they had been at the beginning. (*Ber. Bot. Ges.*
23, 1905, p. 257.) For fuller analysis of all the problems of this
chapter see my Organische Regulationen, my reviews in the *Ergebnisse
der Anatomie und Entwickelungsgeschichte*, vols. viii. xi. xiv., and
my Boston address mentioned above. Compare also Fitting, *Ergebn. d.
Physiol.* vols. iv. and v.

[56] The so-called “inner secretion” in physiology proper would offer a
certain analogy to the facts assumed by such an hypothesis. Compare the
excellent summary given by E. Starling at the seventy-eighth meeting of
the German “Naturforscherversammlung,” Stuttgart, 1906.

But I see quite well that such a theory is very little satisfactory;
for what has to be done in restitution in each case is not a simple
homogeneous act, for which one special material might account, but is
a very complicated work in itself. It was the defect of the theory of
“organ-forming substances” as advocated by Sachs, that it overlooked
this point.

So all we know about the proper stimuli of restitutions is far from
resting on any valid grounds at all; let us not forget that we are
here on the uncertain ground of what may be called the newest and
most up-to-date branch of the physiology of form. No doubt, there
will be something discovered some day, and the idea of the “whole” in
organisation will probably play some part in it. But in what manner that
will happen we are quite unable to predict.

This is the first time that, hypothetically at least, the idea of the
whole has entered into our discussion. The same idea may be said to
have entered it already in a more implicit form in the statement of the
threefold harmony in ontogeny.

Let us now see whether we can find the same problem of the “whole”
elsewhere, and perhaps in more explicit and less hypothetical form.
Let us see whether our analytical theory of development is in fact as
complete as it seemed to be, whether there are no gaps left in it which
will have to be filled up.

3. THE PROBLEM OF MORPHOGENETIC LOCALISATION

α. THE THEORY OF THE HARMONIOUS-EQUIPOTENTIAL SYSTEM

FIRST PROOF OF THE AUTONOMY OF LIFE

We have come to the central point of the first part of these lectures;
we shall try in this chapter to decide a question which is to give life
its place in Nature, and biology its place in the system of sciences.
One of the foundation stones is to be laid upon which our future
philosophy of the organism will rest.

*The General Problem*

Our analytical theory of morphogenesis has been founded upon three
elementary concepts: the prospective potency, the means, and the
formative stimulus. Its principal object has been to show that all
morphogenesis may be resolved into the three phenomena expressed by
those concepts; in other terms, that morphogenesis may be proved to
consist simply and solely of what is expressed by them. Have we indeed
succeeded in attaining this object? Has nothing been left out? Is it
really possible to explain every morphogenetic event, at least in the
most general way, by the aid of the terms potency, means, and stimulus?

All of these questions are apt to lead us to further considerations.
Perhaps these considerations will give us a very clear and simple result
by convincing us that it is indeed possible to analyse morphogenesis in
our schematic way.

But if the answer were a negative one? What would that suggest?

The full analysis of morphogenesis into a series of single formative
occurrences, brought about by the use of given means and on the basis of
given potencies, might assure us, perhaps, that, though not yet, still
at some future time, a further sort of analysis will be possible: the
analysis into the elemental facts studied by the sciences of inorganic
nature. The organism might prove to be a machine, not only in its
functions but also in its very origin.

But what are we to say if even the preliminary analysis, which possibly
might lead to such an ultimate result, fails?

Let us then set to work. Let us try to consider most carefully the topic
in which our concept of the formative cause or stimulus may be said
to be centred, the *localisation* of all morphogenetic effects. Is it
always possible in fact to account for the typical localisation of every
morphogenetic effect by the discovery of a single specific formative
stimulus? You will answer me, that such an analysis certainly is not
possible at present. But I ask you again, are there any criteria that it
is possible, at least in principle; or are there any criteria which will
render such an aim of science impossible for all future time?

*The Morphogenetic “System”*

We know from our experimental work that many, if not all, of the
elementary organs in ontogeny show one and the same prospective
potency distributed equally over their elements. If we now borrow a
very convenient term from mechanics, and call any part of the organism
which is considered as a unit from any morphogenetic point of view, a
morphogenetic “*system*,” we may sum up what we have learnt by saying
that both the blastoderm of the echinoderms, at least around its
polar axis, and also the germ-layers of these animals, are “systems”
possessing an equal potentiality in all of their elements, or, in short,
that they are *equipotential systems*.

But such a term would not altogether indicate the real character of
these systems.

Later on we shall analyse more carefully than before the distribution
of potencies which are the foundation both of regeneration proper and
of adventitious growth, and then we shall see that, in higher plants
for instance, there is a certain “system” which may be called the
organ proper of restitutions, and which also in each of its elements
possesses the same restoring potency; I refer to the well-known cambium.
This cambium, therefore, also deserves the name of an “equipotential
system.” But we know already that its potencies are of the complex
type, that they consist in the faculty of producing the *whole*, of
such a complicated organisation as a branch or a root, that the term
“equipotential system” is here only to signify that such a complicated
unit may arise out of each of the cells of the cambium.

The potencies we have been studying in the blastula or gastrula of
echinoderms are not of the complex type: our systems are equipotential
to the extent that each of their elements may play every *single* part
in the totality of what will occur in the whole system; it is to
this *single* part that the term “function of the position” relates.
We therefore might call our systems equipotential systems with single
potencies; or, more shortly, singular-equipotential systems.

But even this terminology would fail to touch precisely the very
centre of facts: it is not only the simplicity or singularity of
their potencies which characterises the rôle of our systems in
morphogenesis,[57] but far more important with respect to the production
of form are two other leading results of the experimental researches.
The proper act to be performed by every element in each actual case is
in fact a single one, but the potency of any element as such consists
in the possibility of many, nay of indefinitely many, single acts:
that then might justify us in speaking of our systems as “indefinite
equipotential,” were it not that another reason makes another title seem
still more preferable. There are indeed indefinite singular potencies at
work in all of our systems during ontogeny: but the sum of what happens
to arise in every case out of the sum of the single acts performed by
all of the single equipotential cells is not merely a sum but a unit;
that is to say, there exists a sort of harmony in every case among the
*real products* of our systems. The term *harmonious-equipotential
system* therefore seems to be the right one to denote them.

[57] The name of singular-equipotential systems might also be applied
to elementary organs, the single potencies of which are awaked to
organogenesis by specific formative stimuli from without; but that is
not the case in the systems studied in this chapter.

We now shall try first to analyse to its very extremes the meaning of
the statement that a morphogenetic system is harmonious-equipotential.

*The “Harmonious-Equipotential System”*

We have an ectoderm of the gastrula of a starfish here before us; we
know that we may cut off any part of it in any direction, and that
nevertheless the differentiation of the ectoderm may go on perfectly
well and result in a typical little embryo, which is only smaller in
its size than it would normally be. It is by studying the formation of
the highly complicated ciliary band, that these phenomena can be most
clearly understood.

Now let us imagine our ectoderm to be a cylinder instead of being
approximately a sphere, and let us imagine the surface of this cylinder
unrolled. It will give us a plane of two definite dimensions, *a* and
*b*. And now we have all the means necessary for the analytical study of
the differentiation of an harmonious-equipotential system.

Our plane of the dimensions *a* and *b* is the basis of the normal,
undisturbed development; taking the sides of the plane as fixed
localities for orientation, we can say that the actual fate, the
“prospective value” of every element of the plane stands in a fixed and
definite correlation to the length of two lines, drawn at right angles
to the bordering lines of the plane; or, to speak analytically, there
is a definite actual fate corresponding to each possible value of *x*
and of *y*. Now, we have been able to state by our experimental work,
that the prospective value of the elements of our embryonic organ is not
identical with their “prospective potency,” or their possible fate, this
potency being very much richer in content than is shown by a single case
of ontogeny. What will be the analytical expression of such a relation?

Let us put the question in the following way: on what factors does
the fate of any element of our system depend in all possible cases
of development obtainable by means of operations? We may express our
results in the form of an equation:--

*p.v. (X) = f( ... )*

*i.e.* “the prospective value of the element *X* is a function of
...”--of what?

We know that we may take off any part of the whole, as to quantity, and
that a proportionate embryo will result, unless the part removed is of
a very large size. This means that the prospective value of any element
certainly depends on, certainly is a function of, the *absolute size*
of the actually existing part of our system in the particular case. Let
*s* be the absolute size of the system in any actual experimental case
of morphogenesis: then we may write *p.v. (X) = f(s ... )*. But we
shall have to add still some other letter to this *s*.

The operation of section was without restriction either as to the
amount of the material removed from the germ, or as to the direction of
the cut. Of course, in almost every actual case there will be both a
definite size of the actual system and a definite direction of the cut
going hand-in-hand. But in order to study independently the importance
of the variable direction alone, let us imagine that we have isolated
at one time that part of our system which is bounded by the lines *a_1
b_1*, and at another time an equal amount of it which has the lines
*a_2 b_2* as its boundaries. Now since in both cases a typical small
organism may result on development, we see that, in spite of their equal
size the prospective value of every element of the two pieces cut
out of the germ may vary even in relation to the direction of the cut
itself. Our element, *X*, may belong to both of these pieces of the same
size: its actual fate nevertheless will be different. Analytically, it
may be said to change in correspondence to the actual position of the
actual boundary lines of the piece itself with regard to the fundamental
lines of orientation, *a* and *b*; let this actual position be expressed
by the letter *l*, *l* marking the distance of one[58] of the actual
boundary lines of our piece from *a* or *b*: then we are entitled to
improve our formula by writing *p.v. (X) = f(s, l ... )* (Fig.
11).

[58] The distance of the other boundary line from *a* or *b* would be
given by the value of *s*.

[Illustration: Fig. 11.--Diagram to show the Characteristics of an
“Harmonious-equipotential System.”

The element *X* forms part of the systems *a b* or *a_1 b_1* or
*a_2 b_2*; its prospective value is different in each case.]

But the formula is not yet complete: *s* and *l* are what the
mathematicians call variables: they may have any actual value and there
will always be a definite value of *p.v.*, *i.e.* of the actual fate
which is being considered; to every value of *s* and *l*, which as
we know are independent of each other, there corresponds a definite
value of the actual prospectivity. Now, of course, there is also a
certain factor at work in every actual case of experimental or normal
development, which is *not* a variable, but which is the same in all
cases. This factor is a something embraced in the prospective potency
of our system, though not properly identical with it.

The prospective potency of our system, that is to say of each of its
elements, is the sum total of what can be done by all; but the fact
that a typically proportionate development occurs in every possible
case, proves that this sum comes into account, not merely as a sum,
but as a sort of order: we may call this order the “relation of
localities in the absolutely normal case.” If we keep in mind that the
term “prospective potency” is always to contain this order, or, as we
may also call it, this “relative proportionality,” which, indeed, was
the reason for calling our systems “harmonious,” then we may apply it
without further explanation in order to signify the *non-variable*
factor on which the prospective value of any element of our systems
depends, and, if we denote the prospective potency, embracing order,
by the letter *E*, we are now able to complete our formula by saying
*p.v. (X) = f(s, l, E)*. So far the merely analytical study of the
differentiation of harmonious-equipotential systems.[59]

[59] A far more thorough analysis of this differentiation has been
attempted in my paper, “Die Localisation morphogenetischer Vorgänge. Ein
Beweis vitalistischen Geschehens,” Leipzig, 1899.

*Instances of “Harmonious-Equipotential Systems”*

We must try at first to learn a few more positive facts about our
systems, in order that we may know how important is the part which they
play in the whole animal kingdom, and in order that our rather abstract
analysis may become a little more familiar to us. We know already that
many of the elementary morphogenetic organs have been really proved to
be harmonious-equipotential systems, and that the same probably is true
of many others; we also know that the immature egg of almost all animals
belongs to this type, even if a fixed determination of its parts may
be established just after maturation. Moreover, we said, when speaking
about some new discoveries on form-restitution, that there are many
cases in which the processes of restitution do not proceed from single
localities, the seat of complex potencies in the organism, but in which
each *single* part of the truncated organism left by the operation has
to perform one *single* act of restoration, the full restitution being
the result of the totality of all. These cases must now be submitted to
a full analysis.

All of you have seen common sea-anemones or sea-roses, and many of you
will also be familiar with the so-called hydroid polyps. *Tubularia*
is one genus of them: it looks like a sea-anemone in miniature placed
on the top of a stem like a flower. It was known already to Allman
that *Tubularia* is able to restore its flower-like head when that
is lost, but this process was taken to be an ordinary regeneration,
until an American zoologist, Miss Bickford, succeeded in showing that
there was no regeneration process at all, in the proper sense of the
word, no budding of the missing part from the wound, but that the new
tubularian head was restored by the combined work of many parts of the
stem. Further analysis then taught us that *Tubularia* indeed is to be
regarded as the perfect type of an harmonious-equipotential system: you
may cut the stem at whatever level you like: a certain length of the
stem will always restore the new head by the co-operation of its parts.
As the point of section is of course absolutely at our choice, it is
clear, without any further discussion, that the prospective value of
each part of the restoring stem is a “function of its position,” that
it varies with its distance from the end of the stem; and so at once
we discover one of the chief characteristics of our systems. But also
the second point which enters into our formula can be demonstrated in
*Tubularia*: the dependence of the fate of every element on the actual
size of the system. You would not be able to demonstrate this on very
long stems, but if you cut out of a *Tubularia* stem pieces which are
less than ten millimetres in length, you will find the absolute size
of the head restored to be in close relation to the length of the stem
piece, and this dependence, of course, includes the second sort of
dependence expressed in our formula.

The figures will serve to show you a little more concretely what has
been described. The head of *Tubularia* consists of a sort of broad base
with a thin proboscis upon it, both bearing a large number of tentacles;
these tentacles are the first things to be seen as primordia (“Anlagen”)
in the process of restitution. You notice two rings of longitudinal
lines inside the stem; the lines will become walls and then will
separate from the stem until they are only connected with it at their
basal ends; the new tentacles are ready as soon as that has happened,
and a process of growth at the end will serve to drive the new head out
of the so-called perisarc or horny skeleton, which surrounds the stem.
By comparing the two figures, 12 *e*, and *g*, you easily find out that
the absolute lengths of the two tentacle rings are very different, and
that both are in proportion[60] to the actual size of the stem (Fig. 12).

[60] This statement is *not strictly* correct for *Tubularia*. I found
(*Archiv f. Entwickelungsmechanik*, ix. 1899), that a reduction of the
length of the stem is always followed by a reduction of the size of the
hydranth-primordium, but there is no real proportionality between them.
It is only for theoretical simplification that a strict proportionality
is assumed here, both in the text and the diagram. But there is an
almost strict proportionality in all cases of “closed forms.”

[Illustration: Fig. 12.--Tubularia.

*a.* Diagram of the “Hydranth,” with its short and long tentacles.

*b.* Restitution of a new hydranth inside the perisarc (*p*).

*c.* The same--later stage; the tentacles are complete; the whole
hydranth will be driven out of the perisarc by a process of growth that
occurs at the locality marked ⬆.

*d.* A stem of *Tubularia* cut either at *a_1 b_1* or at *a_2 b_2*,
or at *a_1 c*.

*e.* Position of tentacles in the piece cut at *a_1 b_1*.

*f.* Position of tentacles in the piece cut at *a_2 b_2*,
which is equal in length to *a_1 b_1*.

*g.* Position of tentacles in the piece cut at *a_1 c*,
which is half as long as *a_1 b_1*.]

So we find our formula *p.v. (X) = f(s, l, E)* very well
illustrated in *Tubularia*. The formula indeed may help us to predict,
in any case, where a certain part of the polyp’s organisation is
to originate, at least if we know all that is included under our
letter *E*, *i.e.* the normal proportion of our form. Of course such
prediction would not have much practical importance in all our cases of
morphogenesis, but nevertheless I should like to state here that it is
possible; for many scientific authors of recent times have urged the
opinion that prediction of, and domination over, what will happen, can
be the only true aims of sciences at all. I myself judge these aims to
be of second or third-rate importance only, but, if they may be reached
by what our purely theoretical study teaches, so much the better.

Another very typical case of a morphogenetic system of the harmonious
type is supplied by the phenomena of restoration in the ascidian
*Clavellina*. I cannot fully describe the organisation of this form
(Fig. 13a), and it must suffice to say that it is very complicated,
consisting of two very different chief parts, the branchial apparatus
and the so-called intestinal sac; if these two parts of the body of
*Clavellina* are separated one from the other, each may regenerate the
other in the typical way, by budding processes from the wound. But, as
to the branchial apparatus, there may happen something very different:
it may lose almost all of its organisation and become a small white
sphere, consisting only of epithelia corresponding to the germ-layers,
and of mesenchyme between them, and then, after a certain period of
rest, a new organisation will appear. Now this new organisation is
not that of a branchial apparatus but represents a very small but
complete ascidian (Fig. 13). Such a fact certainly seems to be very
important, not to say very surprising; but still another phenomena may
be demonstrated on the animal which seems to be even more important. You
first isolate the branchial apparatus from the other part of the body,
and then you cut it in two, in whatever direction you please. Provided
they survive and do not die, as indeed many of them do, the pieces
obtained by this operation will each lose their organisation, as did the
whole branchial apparatus, and then will each acquire another one, and
this new organisation is also that of a *complete* little *Clavellina*.
So we see that not only is the branchial apparatus of our animal capable
of being transformed into a whole animal by the co-operative work of
all its parts, but even each part of it may be transformed into a small
*whole*, and it is quite at our disposal how large this part shall be,
and what sort of a fragment of the original branchial apparatus it shall
represent.

[Illustration: Fig. 13.--Clavellina.

*a.* Diagram of the normal animal: *E* and *J* = openings; *K* =
branchial apparatus; *D* = intestine; *M* = stomach; *H* = heart.

*b.* The isolated branchial apparatus.

*c-e.* Different stages of reduction of the branchial apparatus.

*f.* The new *whole* little ascidian.]

We could hardly imagine a better instance of an harmonious-equipotential
system.

I cannot give you a description of all the other types of our systems
subservient to restitution, and I can only mention here that the common
hydra and the flatworm *Planaria* are very fine examples of them. But
to one special case of harmonious equipotentiality you must allow me to
direct your further attention.

It has been known for many years that the Protozoa are also capable of
a restoration of their form and organisation after disturbances, if at
least they contain a certain amount of their nuclear substance. This
process of restoration used to be regarded as belonging to the common
type of regeneration proper, until T. H. Morgan succeeded in showing
that in the genus *Stentor* it follows just the very lines which we know
already from our study of embryonic organs or from *Tubularia*; that
an harmonious-equipotential system is at the basis of what goes on.
Now, you know that all Protozoa are but one highly organised cell: we
have therefore here an instance where the so-called “elements” of our
harmonious-morphogenetic system are not cells, but something inside of
cells; and this feature must appear to be of very great moment, for it
first shows, as we have already pointed out on another occasion, that
morphogenesis is not dependent on cell-division, and it states at the
same time that our concept of the harmonious-equipotential system may
cover a very great area--that, in fact, it is a scheme of a very wide
extent.

*The Problem of the Factor* E

We turn back again to considerations of a more abstract form. We left
our analysis of the differentiation of the harmonious-equipotential
systems, and particularly of the phenomena of localisation during this
differentiation, at the point where we had succeeded in obtaining an
equation as the expression of all those factors on which the prospective
value, the actual fate, of any element of our systems depends, *p.v. (X)
= f(s, l, E)* was the short expression of all the relations involved;
*s* and *l*, the absolute size of the system and the relative position
of the element with respect to some fixed points, were independent
variables; *E* was a constant, namely, the prospective potency, with
special regard to the proportions embraced by it.

We shall now study the significance of the factor *E*.

What does this *E* mean? Is it a short expression merely for an actual
sum of elemental agents having a common resultant? And, if so, of what
kind are these agents? Or what may *E* mean, if it can be shown *not* to
be a short sign for a mere sum?

*No Explanation Offered by “Means” or “Formative Stimuli”*

For practical purposes it seems better if we modify the statement of our
question. Let us put it thus: *E* is one of the factors responsible,
among variables, for the localisation of organic differentiation;
what then do we actually know about the causal factors which play a
localising part in organogenesis? We, of course, have to look back to
our well-studied “formative stimuli.” These stimuli, be they “external”
or “internal,” come from without with respect to the elementary organ
in which any sort of differentiation, and therefore of localisation,
occurs: but in our harmonious systems no localising stimulus comes from
without, as was the case, for instance, in the formation of the lens of
the eye in response to the optical vesicle touching the skin. We know
absolutely that it is so, not to speak of the self-evident fact that the
general “means” of organogenesis have no localising value at all.[61]

[61] One might object here that in a piece of a *Tubularia* stem, for
instance, the tissues are in direct contact with the sea-water at
the two points of the wounds only, and that at these very points a
stimulus might be set up--say by a process of diffusion--which gradually
decreases in intensity on its way inward. And a similar argument might
apply to the small but whole blastula of Echinus, and to all other
cases. But, in the first place, stimuli which only differ in intensity
could hardly call forth the typical and typically localised single
features realised in differentiation. On the other hand--and this will
overthrow such an hypothesis completely--the dependence of the single
localised effects in every case on the *absolute size* of the fragment
or piece chosen for restoration renders quite impossible the assumption
that all the singularities in the differentiation of the harmonious
systems might be called forth by single stimuli originating in two
fixed places in an *independent* way. These would never result in any
“harmonious,” any proportionate structure, but a structure of the
“normal” proportionality *and size* at its two ends and non-existent in
the middle!

So we see there is nothing to be done, either with the means or with the
formative stimuli; both are entirely unable to account for those kinds
of localisation during differentiation which appear in our harmonious
systems.

But is there no possibility of explaining the phenomena of organogenetic
localisation by any other sort of interaction of parts? Two such
possibilities may at the first glance seem to exist.

*No Explanation Offered by a Chemical Theory of Morphogenesis*

Though never set forth, in the form of a properly worked-out theory,
the view has sometimes been advocated by biologists, that a chemical
compound of a very high degree of complication might be the very basis
of both development and inheritance, and that such a chemical compound
by its disintegration might direct morphogenesis.

Let us first examine if such a view may hold for the most general
features of organic morphogenesis. It seems to me that from the very
beginning there exists one very serious objection to every chemical
theory of form-building, in the mere fact of the possibility of the
restoration of form starting from atypical localities. The mere fact,
indeed, that there is such a thing as the regeneration of a leg of a
newt--to say nothing about restitution of the harmonious type--simply
contradicts,[62] it seems to me, the hypothesis, that chemical
disintegration of one compound may govern the course of morphogenetic
events: for whence comes the re-existence of the hypothetical compound,
newly to be disintegrated, after disintegration *has* been completed
once already? And we even know that regeneration may go on several times
running from the same locality!

[62] See my article in *Biolog. Centralblatt*, 27, 1907, p. 69. The
question is rendered still more complicated by the fact that in the case
of the regeneration, say, of a leg it is not the original “morphogenetic
compound” which is again required for disintegration, after it has
become disintegrated once already, but only a specific part of it: just
that part of it which is necessary for producing the leg! On the other
hand, it would be impossible to understand, on the basis of physical
chemistry, how the isolated branchial apparatus of *Clavellina* could
be transformed, by chemical processes exclusively, into a system of
which only a certain *part* consists of that substance of which the
starting-point had been composed in its *completeness*.

But, if we intentionally disregard this difficulty, in spite of
its fundamental character, how could the hypothesis of chemical
disintegration give the reason for the differentiation of our
harmonious-equipotential systems, with special regard to the
localisation of it; how could it account, in other words, for the
appearance of typically localised specifications in an organ for which
no external localising causes can be predicated?

Let us remember that a few original intimate differences exist in our
harmonious systems: the main directions of the intimate protoplasmic
structure including polarity and bilaterality. There are therefore
three times two specified poles in each of these systems, at least in
bilateral organisms, but no other differences are present in them.
A few very simple cases of harmonious differentiation might indeed
be understood on the theory of a disintegrating chemical compound
in connection with these few differences. Imagine that the original
compound, of the quantity *a*, is disintegrated to the amount of
*a*_1; from *a*_1 are formed the two more simple compounds, *b*
and *c*, both of them in definite quantities; then we have the three
chemical individuals, *a-a*_1, *b* and *c*, as the constituents of
our harmonious system; and it now might be assumed, without any serious
difficulty, though with the introduction of some new hypotheses, that
the two poles of one of the fundamental axes of symmetry attract *b* and
*c* respectively, *a-a*_1 remaining unattracted between them. We thus
should have the three elementary constituents of the system separated
into three parts, and as they all three are of a definite quantity,
their separation would mean that the system had been divided into three
parts, *a-a*_1, *b* and *c*, also with regard to its proper form.
It is clear, that by taking away any part of the original system, by
means of operations, there would be taken away a certain amount of the
original compound; say that *a/n* is left; then, of course, the three
constituents after the partial disintegration would be *a-a_1/n*,
*b/n* and *c/n*, and so it follows that the proportionality of
localisation would really be preserved in any case.

But these considerations, evident as they seem to be in the most
simple case, fail to satisfy in a really general sense: for two
different reasons. First, they could never account for the fact that
the differentiated organism by no means consists of so many different
compounds as it shows single parts of its differentiation, but that,
on the contrary, it only consists, as we know, of a certain rather
limited number of true different morphogenetic elements, these
elements occurring again and again--as for instance, nervous or
muscular elements--but typical each time in locality, quantity, and
form. And in the second place, the very *form* of elementary organs,
their form as such, does not at all go hand-in-hand with chemical
differences; this feature alone would absolutely overthrow any sort
of a chemical morphogenetic theory to account for the problem of
localisation. Take the typically arranged ring of the mesenchyme
cells in our Echinus-gastrula, with its two spherical triangles, so
typically localised; look at any sort of skeleton, in Radiolaria, or in
starfishes, or in vertebrates: here you have form, real form, but form
consisting of only one material. Not only is the arrangement of the
elements of form typical here, *e.g.* the arrangement of the single
parts of the skeleton of the hand or foot, but also the special form
of each element is typical, *e.g.* the form of each single bone of the
foot; and, on a purely chemical theory of morphogenesis the sufficient
reason for the production of typical form in such a sense would be
wanting. For atoms or molecules by themselves can only account for form
which is arranged, so to speak, according to spatial geometry--as in
fact they do in crystallography; but they can never account for form
such as the skeleton of the nose, or hand, or foot. You will answer
me perhaps, that there may be non-chemical agents in the germ,[63]
responsible for typical form-localisation, but by such reasoning you
would be departing from a purely chemical theory. Our next paragraph
will be devoted to this side of the question.

[63] Besides the specified poles determined by the polar-bilateral
structure of the protoplasm.

That is the principal reason for rejecting all sorts of chemical
morphogenetic theories put forward to explain the problem of
localisation; it is more explicit, and therefore, I suppose, still
more convincing than the more general consideration that the very
fact of restitutions in itself must contradict the hypothesis that
a disintegration of compounds might be the directive agency in
morphogenesis. To sum up: Specificity of organic form does not go
hand-in-hand with specificity of chemical composition, and therefore
cannot depend on it; and besides that, specific organic form is such
that it can never be explained by atomic or molecular arrangement in
the chemical sense; for, to state it in a short but expressive manner,
the “form” of an atom or molecule can never be that of a lion or a
monkey. To assume that would be to go beyond the limits of chemistry in
chemistry itself.

*No Machine Possible Inside the Harmonious Systems*

And now we turn to the last possibility which is left to us in our
endeavour to “understand” the localisation of the differentiation in our
harmonious-equipotential systems by the means of physics and chemistry.
Outside causes have failed to account for it, chemical disintegration
of a compound has failed too. But could there not exist some sort of
complicated interactions amongst the parts of the harmonious system
themselves? Could there not exist some kind of a real machine in the
system, which, if once set going, would result in the differentiations
that are to take place? Then we might say that the “prospective
potency” of the system is in fact that machine; we should know what the
letter *E* of our equation stood for: viz., a resultant action of many
complicated elemental interactions, and nothing more.

Weismann, we know already, had assumed that a sort of machine was the
prime mover of morphogenesis. We have seen that his theory cannot be
true; the results of experiments most strongly contradict it. But, of
course, the experiments only showed us that *such* a machine as *he*
had imagined to exist could not be there, that development could not be
governed by the disintegration of a given complicated structure into its
simplest parts. But might not some other machine be imaginable?

We shall understand the word “machine” in a most general sense. A
machine is a typical configuration of physical and of chemical
constituents, by the acting of which a typical effect is attained.
We, in fact, lay much stress upon embracing in our definition of a
machine the existence of chemical constituents also; we therefore
understand by the word “machine” a configuration of a much higher
degree of complication than for instance a steam-engine is. Of course
a machine, whose acting is to be typical with regard to the three
dimensions in space, has to be typically constructed with regard to
these three dimensions itself; a machine that was an arrangement of
elements in a strict plane could never have typical effects at right
angles to that plane. This is a point which must well be kept in mind
in all hypothetical considerations about machines that claim to explain
morphogenesis.

It must be granted that a machine, as we understand the word, might very
well be the motive force of organogenesis in general, if only normal,
that is to say, if only undisturbed development existed, and if a taking
away of parts of our systems led to fragmental development.

But we know that, at least in our harmonious-equipotential systems,
quite another process occurs after parts have been taken away: the
development that occurs is not fragmental but whole, only on a smaller
scale.

And we know, further, that this truly whole development sets in
irrespective of the amount and direction of the separation. Let us first
consider the second of these points. There may be a whole development
out of each portion of the system--above certain limits--which is, say,
of the volume *V*. Good! Then there ought to exist a machine, like
that which exists in the whole undisturbed system, in this portion *V*
also, only of smaller dimensions; but it also ought to exist in the
portion *V*_1 which is equal to *V* in amount, and also in *V*_2, in
*V*_3, *V*_4 and so on. Indeed, there do exist almost indefinitely
many *V*_n all of which can perform the whole morphogenesis, and all
of which therefore ought to possess the machine. But these different
portions *V*_n are only partly different from each other in spatial
relation. Many parts of *V*_2 are also parts of *V*_1 and of *V*_3
and of *V*_4 and so on; that is to say, the different volumes *V*_n
overlap each other successively and in such a manner that each following
one exceeds the preceding one in the line by a very small amount only.
But what then about our machines? Every volume which may perform
morphogenesis completely must possess the machine in its totality. As
now every element of one volume may play any possible elemental rôle in
every other, it follows that each part of the whole harmonious system
possesses any possible elemental part of the machine equally well, all
parts of the system at the same time being constituents of different
machines.

A very strange sort of machine indeed, which is the same in all its
parts (Fig. 14)!

[Illustration: Fig. 14.--An “Harmonious-equipotential System” of
whatever kind.

According to the “machine-theory” of life this system ought to possess
a certain unknown very complicated machine *in its completeness*:

(*a*) in its total length,
and (*b*) in each of the equal volumes *v*, *v*_1, *v*_2, *v*_3 and
so on,
and (*c*) in each of the unequal volumes *w*, *x*, *y*, and so on,
and (*d*) in every imaginable volume, no matter of what size.

Therefore the “machine-theory” of life is absurd.]

But we have forgotten, I see, that in our operation the absolute amount
of substance taken away from the system was also left to our choice.
From this feature it follows that not only all the different *V*_n,
all of the same size, must possess the hypothetic machine in its
completeness, but that all amounts of the values *V*_n-*n*, *n* being
variable, must possess the totality of the machine also: and all values
*V*_n-*n*, with their variable *n*, may again overlap each other.

Here we are led to real absurdities!

But what is the conclusion of our rather wild considerations?

It seems to me that there is only one conclusion possible. If we
are going to explain what happens in our harmonious-equipotential
systems by the aid of causality based upon the constellation of single
physical or chemical factors and events, there *must* be some such
thing as a machine. Now the assumption of the existence of a machine
proves to be absolutely absurd in the light of the experimental facts.
*Therefore there can be neither any sort of a machine nor any sort of
causality based upon constellation underlying the differentiation of
harmonious-equipotential systems.*

For a machine, typical with regard to the three chief dimensions
of space, cannot remain itself if you remove parts of it or if you
rearrange[64] its parts at will.

[64] The pressure experiments and the dislocation experiments come into
account here; for the sake of simplicity they have not been alluded to
in the main line of our argument.

Here we see that our long and careful study of morphogenesis has been
worth while: it has afforded us a result of the very first importance.

*The Autonomy of Morphogenesis Proved*

No kind of causality based upon the constellations of single physical
and chemical acts can account for organic individual development; this
development is not to be explained by any hypothesis about configuration
of physical and chemical agents. Therefore there must be something
else which is to be regarded as the sufficient reason of individual
form-production. We now have got the answer to our question, what
our constant *E* consists in. It is not the resulting action of a
constellation. It is not only a short expression for a more complicated
state of affairs, it expresses *a true element of nature*. Life, at
least morphogenesis, is not a specialised arrangement of inorganic
events; biology, therefore, is not applied physics and chemistry: life
is something apart, and biology is an independent science.

All our results at present, indeed, are negative in their form; our
evidence was throughout what is called *per exclusionem*, or indirect
or apagogic. There were excluded from a certain number of possibilities
all except one; a disjunctive proposition was stated in the form: *E*
is either this, or that, or the other, and it was shown that it could
not be any of all these except one, therefore it was proved to be that
one. Indeed, I do not see how natural science could argue otherwise;
no science dealing with inorganic phenomena does; something new and
elemental must always be introduced whenever what is known of other
elemental facts is proved to be unable to explain the facts in a new
field of investigation.

We shall not hesitate to call by its proper name what we believe we have
proved about morphogenetic phenomena. What we have proved to be true
has always been called *vitalism*, and so it may be called in our days
again. But if you think a new and less ambitious term to be better for
it, let us style it the doctrine of the *autonomy of life*, as proved
at least in the field of morphogenesis. I know very well that the word
“autonomy” usually means the faculty of *giving* laws to oneself, and
that in this sense it is applied with regard to a community of men;
but in our phrase autonomy is to signify the *being subjected* to laws
peculiar to the phenomena in question. This meaning is etymologically
defensible, and besides that I perhaps may remind you of a certain
chapter of Professor Ward’s Gifford Lectures, in which he holds the view
that, psychologically and epistemologically, there is more than a mere
verbal relation between the civil and the natural “law.”

Vitalism then, or the autonomy of life, has been proved by us
indirectly, and cannot be proved otherwise so long as we follow the
lines of ordinary scientific reasoning. There can indeed be a sort of
direct proof of vitalism, but now is not the time to develop this proof,
for it is not of the purely scientific character, not so naïve as our
present arguments are, if you choose to say so. An important part of our
lectures next summer will be devoted to this direct proof.

“*Entelechy*”

But shall we not give a name to our vitalistic or autonomous factor
*E*, concerned in morphogenesis? Indeed we will, and it was not without
design that we chose the letter *E* to represent it provisionally. The
great father of systematic philosophy, Aristotle, as many of you will
know, is also to be regarded as the founder of theoretical biology.
Moreover, he is the first vitalist in history, for his theoretical
biology is throughout vitalism; and a very conscious vitalism indeed,
for it grew up in permanent opposition to the dogmatic mechanism
maintained by the school of Democritus.

Let us then borrow our terminology from Aristotle, and let that factor
in life phenomena which we have shown to be a factor of true autonomy be
called *Entelechy*, though without identifying our doctrine with what
Aristotle meant by the word έντελέχεια. We shall use this word only as a
sign of our admiration for his great genius; his word is to be a mould
which we have filled and shall fill with new contents. The etymology of
the word ἐντελέχεια allows us such liberties, for indeed we have shown
that there is at work a something in life phenomena “which bears the end
in itself,” ὃ ἔχει ἐν ἑαυτᾣ τὸ τέλος.

Our concept of entelechy marks the end of our analysis of individual
morphogenesis. Morphogenesis, we have learned, is “epigenesis” not only
in the descriptive but also in the theoretical sense: manifoldness
in space is produced where no manifoldness was, real “evolutio” is
limited to rather insignificant topics. But was there nothing “manifold”
previous to morphogenesis? Nothing certainly of an *extensive*
character, but there was something else: there was entelechy, and thus
we may provisionally call entelechy an “*intensive manifoldness*.”
That then is our result: not evolutio, but epigenesis--“epigenesis
vitalistica.”

*Some General Remarks on Vitalism*

We now shall leave entelechy where it stands: next summer we shall turn
back to it and shall make its full logical and ontological analysis
our chief study. At present we are satisfied with having proved its
existence in nature, with having laid some of the foundations of a
doctrine to be based upon it. I hope that these foundations will evince
themselves strong: that is all-important.[65] It indeed has been the
fault of all vitalism in the past that it rested on weak foundations.
Therefore the discussion of the basis underlying our doctrine of the
autonomy of life is to occupy us still a considerable time. We shall
devote to it two more of this year’s lectures and three of the next; we
shall examine all sorts of phenomena of life in order to find out if
there are any further proofs of vitalism, independent perhaps, of what
we way call our *first proof*, which is based upon the analysis of the
*differentiation of harmonious-equipotential systems*. We shall find
some more independent proofs; and besides that we shall find many kinds
of phenomena upon which future times perhaps may erect more of such
independent proofs.

[65] My “first proof of vitalism” was first developed in the paper, “Die
Localisation morphogenetischer Vorgänge,” Leipzig, 1899. (See additional
remarks in *Organische Regulationem*, Leipzig, 1901, and in *Archiv
für Entwickelungsmechanik*, 14, 1902.) I cannot admit that any really
serious objection has been brought forward against it. (See my articles
in *Biologisches Centralblatt*, 22, 23, 27, and in *Ergebnisse d. Anat.
u. Entwickelungsgesch*. 11, 14.) An historical sketch of vitalism will
be found in my book, *Der Vitalismus als Geschichte und als Lehre*,
Leipzig, 1905.

For we shall be chary of bestowing the name “proof” except on what is a
proof indeed, of course according to our critical conviction. Vitalistic
views in biology have arisen in rather numerous forms during the last
fifteen years, especially in Germany--though in very strong contrast to
the so-called official German biology--but I can only admit that one of
all the arguments of “neo-vitalism” has proved its statements. I refer
to the theory of “morphaesthesia” as developed by Noll, which we shall
study briefly in the next lecture. I cannot concede that Reinke or
Schneider or Pauly have really proved what they believe, and I cannot
even allow to the most original thinker in this field, Gustav Wolff,
that he has given a real demonstration of his views. He states that the
existence of so-called “primary purposefulness,” that is, the existence
of adaptive processes, which cannot be imagined to have arisen on
Darwinian principles, is able to prove vitalism; but I say that it only
proves teleology, which is a broader concept than vitalism.

The possibility of a machine at the root of the phenomena in question
always has to be excluded in order that vitalism may be proved, and I
cannot grant that the necessity of such an exclusion has been actually
shown by any of my fellow-combatants against so-called mechanism, except
Noll.[66]

[66] We are dealing here with morphogenesis and so-called vegetative
physiology only; to certain psychologists, who have refuted the theory
of psycho-physical parallelism, I must grant that they also have proved
vitalism. (See Volume II.)

*The Logic of our First Proof of Vitalism*

Let us devote the end of our present lecture to an account of the
logical means by which it has been possible to develop what we hope will
be regarded as a true *proof* of life autonomy.

Firstly, we have looked upon the phenomena of morphogenesis without
any prepossessions; we may say that we have fully surrendered ourselves
to them; we have not attacked them with any sort of dogmatism except
the inherent dogmatism of all reasoning. But this dogmatism, if it may
be called so, does not postulate that the results of the inorganic
doctrines must hold for the organic world, but only that both the
inorganic and the organic must be subject to certain most general
principles.

By studying life as a given phenomenon, by fully devoting ourselves to
our problem, we not only have analysed into its last elements what was
given to us as our subject, but we also, more actively, have created new
combinations out of those elements: and it was from the discussion of
these positive constructions that our argument for vitalism was derived.

We have analysed morphogenesis into elementary processes, means,
potency, formative stimulus, just as the physicist analyses mechanics
into time, velocity, mass, and force; we have then rearranged
our elements into “systems”--the equipotential systems, the
harmonious-equipotential system in particular, just as the physicist
composes his elements into the concepts of momentum or of kinetic energy
or of work. And finally, we have discussed our compositions and have
obtained our result, just as the physicist gets his ultimate results by
discussing work and kinetic energy and momentum.

Of course the comparison is by no means intended to show that mechanics
and biology are sciences of the same kind. In my opinion, they are not
so at all; but nevertheless there do exist similarities of a logical
kind between them.

And it is not the formal, logical character alone which allows us to
compare biology with other natural sciences: there is still something
more, there is one kind of assumption or postulate, or whatever you
may choose to call it, without which all science whatever would be
altogether *impossible*. I refer to the concept of *universality*. All
concepts about nature which are gained by positive construction out of
elements resulting from analysis, claim to be of *universal validity*;
without that claim there could indeed be no science.

Of course this is no place for a lecture on methodology, and it
therefore must suffice to make one remark with special regard to
our purpose, which we should like to emphasise. Our concept of the
harmonious-equipotential system--say rather, our concept of the
prospective potency itself--presumes the understanding that indeed *all*
blastomeres and *all* stems of *Tubularia*, including those upon which
we have *not* carried out our experiments, will behave like those we
have experimented with; and those concepts also presume that a certain
germ of Echinus, *A*, the blastomeres of which were not separated,
would have given two whole larvae, if separation had taken place, while
another germ, *B*, which actually gave us two larvae after separation,
would only have given one without it. Without this presumption the
concept of “potency” is meaningless, and, indeed, every assumption of a
“faculty” or a “possibility” would be meaningless in the whole area of
science.

But this presumption can never be proved; it can only be postulated. It
therefore is only with this postulate that our first proof of vitalism
holds; but this restriction applies to *every* law of nature.

I cannot force you to agree with this postulate: but if you decline
you are practically saying that there exists a sort of pre-established
harmony between the scientific object and the scientist, the scientist
always getting into his hands such objects only as have been
predestinated from the very beginning to develop two larvae instead of
one, and so on.

Of course, if that is so, no proof of natural laws is possible at all;
but nature under such views would seem to be really dæmonic.

And so, I hope, you will grant me the postulate of the universality
of scientific concepts--the only “hypothesis” which we need for our
argument.

4. ON CERTAIN OTHER FEATURES OF MORPHOGENESIS ADVOCATING ITS AUTONOMY

Our next studies on the physiology of form will be devoted in the first
place to some additional remarks about our harmonious-equipotential
systems themselves, and about some other kinds of morphogenetic
“systems” which show a certain sort of relationship with them. For it is
of the greatest importance that we should become as familiar as possible
with all those facts in the physiology of form upon the analysis of
which are to be based almost all of the future theories that we shall
have to develop in biology proper and philosophical. Our discussions, so
far as they relate to questions of actual fact, will contain only one
other topic of the same importance.

But though it is designed to complete and to deepen our analysis,
the present considerations may yet be said to mark a point of rest
in the whole of our discussions: we have followed one single line of
argumentation from the beginning until now; this line or this stream of
thought, as you might call it, is now to break into different branches
for a while, as if it had entered from a rocky defile into a plain.
It seems to me that such a short rest will be not unconducive to a
right understanding of all we have made out; and such a full and real
conceiving again, such a realising of our problems of morphogenesis and
their solutions, will be the best preparation for the philosophical part
of these lectures.

HARMONIOUS-EQUIPOTENTIAL SYSTEMS FORMED BY WANDERING CELLS

All of the harmonious-equipotential systems which we have studied so
far were the bases of histological differentiation; that is to say, the
processes of their differentiation consisted in specifically localised
elements of theirs becoming different *in situ*. Now we know at least
one type of systems which also may be called harmonious-equipotential,
but the differentiation of which does not simply relate to elements at
a fixed place. An additional phenomenon enters here into the sphere of
the others. The elements not only become different where they are, but
a specific changing of locality, a specific kind of wandering, goes
hand-in-hand with differences relating to the prospective value to be
attained. I am speaking of the formation of the larval skeleton of
our well-known Echinus. We know that the mesenchyme cells, which have
left the blastoderm and are arranged in a sort of ring of bilateral
structure, are the starting-point of this skeleton: it indeed originates
in a sort of secretive process on the part of the cells; the cells
are moving about and are secreting carbonate of lime during their
wandering. The experiments now have shown, as we know, that a whole,
though smaller, skeleton may also be formed, if only a half or a quarter
of the mesenchyme cells are present, as happens to be the case in all
experiments with isolated blastomeres of the two or four-cell stage of
cleavage. It is clear that in these cases the performance of each single
cell must be different from what it is in the normal case, and that
the same sort of differences in the morphogenetic performances appears
again, if the two- and the four-cell stage are compared with each other.
And there are still some other phenomena showing the possibility of
different performances being carried out by the individual cells. Peter
has shown that the number of mesenchyme cells may vary enormously under
certain conditions; but, in spite of that, the skeleton always will
be complete. It may be said that this line of research is only of a
relative value to our own questions, as, of course, variability relates
to different individuals: but it seems to me that it adds a very good
supplementary instance to what the experiment on the individual itself
has established.

We should only be repeating ourselves if we were to analyse again what
happens here as the expression of the harmonious-equipotentiality
itself. But indeed there occurs something new in this instance: the
single mesenchyme cell not only has to perform in each case that single
act of specific secretion which the case requires, but it also has to
wander to the right place in order to perform it; there must be some
order, not only about the acts of secretion after wandering, but also in
the migrations themselves. If undisturbed ontogeny alone were possible,
and if therefore a theory like that of Weismann were in place, we might
say perhaps that each mesenchyme-cell is specified not only as to its
performance in secretion, but also with regard to its chemotactical
irritability, the latter being typically localised, so that its effect
becomes typical, thanks to the typical arrangement of all the cells
with respect to each other. But that is certainly not the case. Now, you
may ask yourselves if you could imagine any sort of a machine, which
consists of many parts, but not even of an absolutely fixed number, all
of which are equal in their faculties, but all of which in each single
case, in spite of their potential equality, not only produce together
a certain typical totality, but also arrange themselves typically in
*order* to produce this totality. We *are* indeed familiar with certain
occurrences in nature where such curious facts are observed, but I doubt
if you would speak of “machines” in these cases. The mesenchyme-cells,
in fact, behave just as a number of workmen would do who are to
construct, say, a bridge. All of them *can* do every single act, all of
them also *can* assume every single position: the result always is to
be a perfect bridge; and it is to be a perfect bridge even if some of
the workmen become sick or are killed by an accident. The “prospective
values” of the single workman change in such a case.

I well know that it is only an analogy which I am offering to you.
The mesenchyme-cells have not “learned,” have no “experience.” All
that is to occupy us next summer. But in spite of it, there is truth
in the analogy; and perhaps you will prefer it to the merely abstract
consideration.

ON CERTAIN COMBINED TYPES OF MORPHOGENETIC SYSTEMS

For the sake of completeness it may be remarked, only by the way, that
the type of the proper harmonious-equipotential system may go hand in
hand with another type of “systems” which play a part in morphogenesis;
a type which we have shortly mentioned already and which will be studied
fully a few chapters later. We know that there are equipotential systems
with complex potencies: that is to say, systems which may produce a
whole organism equally well from any one of their elements; we know the
cambium of Phanerogams to be such a system. Now it is easily understood
that the germ of our Echinus, say in the stage of two or four or eight
cleavage cells, is not only an harmonious-equipotential system, but
a complex-equipotential system too. Not only may there arise a whole
organism out of 2/4 or 3/4 or 3/8, 4/8, 5/8, 6/8, 7/8 of its elements,
in which cases the harmonious rôle of the single element with regard to
its single performance in a totality is variable, but there may also
arise four whole single larvae out of the four cells of the four-cell
stage, or eight single whole larvae out of the eight-cell stage.[67]
In these cases, of course, each of the four or eight elements has
performed not a part of the totality, changing with its “position,” but
the totality itself. With respect to these possible performances the
“systems” present in the four or eight-cell stages of cleavage must be
called complex-equipotential ones.

[67] The eight larvae would be incomplete in some respect, but not with
regard to symmetry. They would be “whole” ones, only showing certain
defects in their organisation. See page 65 note 1, and page 73.

We propose to give the name of *mixed-equipotential systems* to all
those equipotential systems which, at the same time, may be regarded
as belonging to the harmonious or to the complex type. It is not only
among cleavage-stages that they are to be found; you may also find them
very clearly exhibited in our ascidian *Clavellina* for instance. We
know already that the branchial apparatus of this form is typically
harmonious-equipotential, but it is complex-equipotential too, for it
also may regenerate what is wanting in the proper way, by a budding
from the wound; and the same is true of many other cases, the flatworm
*Planaria* for instance.

Another type of systems, which might be said to be of a higher degree,
is exhibited in some very strange phenomena of regeneration. It was
first shown most clearly by some experiments of Godlewski’s that a
whole tail may be regenerated from a wound inflicted on the body of
a newt, even if this wound involves section of only a portion of the
body-diameter. Section of the whole of the body-diameter of course
would cause the formation of the whole tail also; but it was found that
even an incomplete cross-section of the body is capable of performing
the whole on a smaller scale. The series of possible cross-sections
which are all capable of regeneration would have to be called a
system of the complex type in this case; but, now we learn that every
*single* cross-section is of the harmonious type, we must speak of
*complex-harmonious systems*. What we have described is not the only
instance of our new type of morphogenetic systems. Some other instances
had been discovered a few years earlier, though nobody had pointed
out their true significance. In the flatworm *Planaria* a partial
cross-section is also capable of forming a whole structure, say a head,
and all cases of so-called “super-regeneration” after the infliction of
a complicated wound probably belong here also.

You may say that our two additions to the theory of systems are merely
formal, and indeed I am prepared to concede that we shall not learn
anything altogether new from their discussion: their analysis would lead
either to what was our “first proof” of the autonomy of life-phenomena
or to what will be our “second” one. But the mere descriptions of the
facts discovered here will interest you, I think, and will fill your
minds with more vivid pictures of the various aspects of form-autonomy.

While dealing with our harmonious-equipotential systems as the
starting-points of processes of restitution, *e.g.* in *Tubularia*,
*Clavellina*, the flatworms, and other instances, we always have
regarded cross-sections of the body as constituting the elements of
equipotentiality. Now cross-sections, of course, are by no means simple
in themselves, but are made up of very different tissues, which are
derivates of all three of the original germ layers--ectoderm, mesoderm,
and endoderm. Owing to this composite character of the cross-sections,
taken as elements of harmonious systems, a special phenomenon of
morphogenesis is presented to us, which teaches somewhat more than the
mere concept of harmonious-equipotentiality can express. If composite
elements concerned in morphogenesis result in one whole organisation
in spite of the development of the single tissues of these elements
going on independently, then there must be a sort of correspondence
or reciprocity of the harmonious development among these tissue
constituents themselves; otherwise a proportionate form could not be the
final result. We may conveniently speak of a *reciprocity of harmony* as
existing between the single tissues or germ layers which constitute many
harmonious-equipotential systems, and there can be little doubt that we
have here an important feature with regard to general morphogenesis.[68]

[68] Reciprocal harmony may be reduced in some cases to the given
proportions of one original harmonious system, from which the single
constituents of the complicated system, showing reciprocal harmony, are
derived. Then we have only an instance of “harmony of constellation”
(see p. 109). But reciprocal harmony seems to become a problem itself,
if it occurs in restitutions starting from quite a typical point,
selected by the experimenter. It will be a problem of future research
to give an exact formula of what happens here. Reciprocal harmony also
occurs in regeneration proper. It is known that the formation of the
regenerative bud and the differentiation of this bud follow each other.
As the bud is composed of different elementary systems, it follows that
these different systems, of which every single one is harmonious, also
have to work in reciprocity to each other, in order that one whole
proportionate formation may result.

A few other groups of morphogenetic facts may find their proper place
here, though they are not properly to be regarded as additions to the
theory of harmonious systems but as forming a sort of appendix to it.

THE “MORPHAESTHESIA” OF NOLL[69]

[69] *Biol. Centralblatt.* 23, 1903.

We may briefly mention that group of botanical phenomena, by which
the botanist Noll has been led to the concept of what he calls
“morphaesthesia,” or the “feeling” for form; a concept, the full
discussion of which would lead to almost the same conclusions as our
analysis of the harmonious systems has done. In the Siphoneae, a
well-known order of marine algae with a very complicated organisation
as to their exterior form, the protoplasm which contains the nuclei is
in a constant state of circulation round the whole body, the latter
not being divided by proper cell-walls. On account of this constant
movement it is certainly impossible to refer morphogenetic localisation
to definite performances of the nuclei. Nor can any sort of structure
in the outer protoplasmic layer, which is fixed, be responsible for
it, for there is no such structure there: hence there must be a sort
of feeling on the part of the plant for its relative body localities,
and on account of this feeling morphogenesis occurs. This “feeling” is
styled “morphaesthesia” by Noll, and to it he tries to refer all sorts
of different botanical form-phenomena,[70] for instance what is called
“autotropism,” that is, the fact that branches of plants always try to
reassume their proper angle with regard to their orientation on the main
axis, if this orientation has been disturbed. It may be an open question
if this particular application of the theory is right: certainly
there seems to be much truth in the establishment of the concept of
morphaesthesia, and we only have to object to its psychological name.
But that may be done in a more general form on a later occasion.

[70] Certain phenomena of the physiology of growth of *Geranium
Robertianum*, recently discussed by Francé from a vitalistic point of
view (*Zeitschr. Entw. lehre*. 1, 1907, Heft iv.), might also belong
here. I cannot see an independent proof of vitalism in these facts if
taken by themselves; a pre-existing “machine” cannot be absolutely
excluded here.

RESTITUTIONS OF THE SECOND ORDER

In the hydroid polyp *Tubularia*, already familiar to us as being a most
typical representative of the harmonious-equipotential systems, a very
interesting phenomenon has been discovered[71], almost unparalleled at
present but nevertheless of a general importance, a phenomenon that
we may call a restitution of a restitution, or a restitution of the
second order. You know that the first appearance of the new head of
*Tubularia*, after an operation, consists in the formation of two rings
of red lines, inside the stem, these rings being the primordia of the
new tentacles. I removed the terminal ring by a second operation soon
after it had arisen, disturbing in this way the process of restitution
itself: and then the process of restitution itself became regulated. The
organism indeed changed its course of morphogenesis, which was serving
the purposes of a restitution, in order to attain its purpose in spite
of the new disturbance which had occurred. For instance, it sometimes
formed two rings out of the one that was left to it, or it behaved
in a different way. As this difference of morphogenetic procedure is
a problem by itself, to be discussed farther on, we shall postpone a
fuller description of this case of a restitution of the second degree.

[71] Driesch, *Arch. Entw. Mech.* 5, 1897.

At present I do not see any way of proving independently the autonomy of
life by a discussion of these phenomena; their analysis, I think, would
again lead us to our problem of localisation and to nothing else; at
least in such an exact form of reasoning as we demand.

ON THE “EQUIFINALITY” OF RESTITUTIONS[72]

[72] Driesch, *Arch. Entw. Mech.* 14, 1902.

I have told you already that *Tubularia* in the phenomena of the
regulation of restitutions offers us a second problem of a great general
importance, the problem of the *Equifinality of Restitutions*. There
indeed may occur restitutions, starting from one and the same initial
state and leading to one and the same end, but using very different
means, following very different ways in the different individuals of one
and the same species, taken from the same locality, or even colony.

Imagine that you have a piece of paper before you and wish to sketch
a landscape. After drawing for some time you notice that you have
miscalculated the scale with regard to the size of the paper, and
that it will not be possible to bring upon the paper the whole of the
landscape you want. What then can you do? You either may finish what you
have begun to draw, and may afterwards carefully join a new piece of
paper to the original one and use that for the rest of the drawing; or
you may rub out all you have drawn and begin drawing to a new scale; or
lastly, instead of continuing as you began, or erasing altogether, you
may compromise as best you can by drawing here, and erasing there, and
so you may complete the sketch by changing a little, according to your
fancy, the proportions as they exist in nature.

This is precisely analogous to the behaviour of our *Tubularia*.
*Tubularia* also may behave in three different ways, if, as I described
to you, the terminal one of its two newly arisen rings of tentacle
primordia is removed again. It may complete what is left, say the basal
tentacle ring, then put forth from the horny skeleton (the “perisarc”)
the new head as far as it is ready, and finally complete this head
by a regular process of budding regeneration. But it also may behave
differently. It may “erase” by a process of retro-differentiation all
that has been left of what had already been formed, and then may form
*de novo* the totality of the primordia of a new head. Or, lastly, it
may remove a part of the middle of the one ring of tentacle rudiments
which was left, and may use this one ring for the formation of two,
which, of course, will not be quite in the normal relations of place
with regard to each other and to the whole, but will be regulated
afterwards by processes of growth. Thus, indeed, there is a sort of
equifinality of restitution: one starting-point, one end, but three
different means and ways.

It would, of course, contradict the principle of univocality, as we
shall see more fully later on, to assume that there actually are
different ways of regulation whilst all the conditions and stimuli are
the same. We are obliged to assume, on the contrary, that this is not
the case, that there are certain differences in the constellation, say
of the general conditions of age or of metabolism, which are responsible
for any given individual choosing one process of restitution instead
of another; but even then the phenomenon of equifinality remains very
striking.

It has long been known that restitution in general does not always
follow the same lines of morphogenesis as are taken by ontogeny, and it
was this feature that once led Roux to point out that the adult forms
of organisms seem to be more constant than their modes of origin. But,
comparing ontogeny with restitution in general, we see that only the
ends are the same, not the points of starting; the latter are normal or
non-typical in ontogeny, atypical in restitution. In the new discoveries
of an equifinality of restitutions we have the *same* starting-point,
which is decidedly non-typical but atypical, *i.e.* dependent on our
arbitrary choice, leading by *different* ways always to the *same* end.

There may be many who will regard the fact of equifinality as a proof of
vitalism. I should not like to argue in this easy way; I indeed prefer
to include part of the phenomena of equifinality in our first proof of
autonomy, and part in the second one, which is to follow.

Another important phenomenon of the equifinality of regulation was
discovered by Morgan. A species of the flatworm *Planaria* was found to
restore its totality out of small pieces either by regeneration proper,
if the pieces were fed, or by a sort of rearrangement of material,
on the basis of its harmonious-equipotentiality, if they were kept
fasting. It is important to note that here we see one of the conditions
determining the choice of the way to restoration, as we also do in the
well-known equifinal restitutions of the root in plants, where the
behaviour of the organism depends on the distance of the operation-wound
from the tip.[73] In *Tubularia* the actual stage of restitution that
has been already reached by the stem when the second operation takes
place, may account for the specification of its future organogenesis,
but this is not at all clearly ascertained at present.

[73] The root may be restored by regeneration proper, or by the
production of adventitious roots, or by one of the side-roots changing
its geotropism from horizontal to positive, according to the smaller or
greater distance of the wound from the tip.

*Clavellina* also shows equifinality in its restitution, as has already
been shortly mentioned. The isolated branchial apparatus may restitute
itself by retro-differentiation to an indifferent stage followed by
renovation; or it may regenerate the intestine-sac in the proper way.
Nothing is known here about the conditions, except perhaps that young
individuals seem more apt to follow the first of these two ways, older
ones the second; but there are exceptions to this rule.

The discussion of other instances of equifinality, though important in
themselves, would not disclose anything fundamentally new, and so we may
close the subject with the remark that nothing can show better than the
fact of the equifinality of restitutions how absolutely inadequate all
our scientific conceptions are when confronted with the actual phenomena
of life itself. By analysis we have found differences of potencies,
according as they are simple or complex; by analysis we have found
differences of “systems,” differences of means, and indeed we were glad
to be able to formulate these differences as strictly as possible: but
now we see how, in defiance of our discriminations, one and the same
species of animals behaves now like one sort of our “systems,” and now
like the other; how it uses now one sort of “potencies,” now another.

But even if it is granted that, in the presence of such phenomena of
life, our endeavour seems to be like a child’s play on the shores of the
ocean, I do not see any other way for us to go, so long, at least, as
our goal is human science--that is, a study of facts as demanded by our
mental organisation.

REMARKS ON “RETRO-DIFFERENTIATION”

We shall finish this part of our studies by mentioning a little more
explicitly one fundamental fact which has already entered incidentally
into our considerations, viz. *retro-* or *back-differentiation*.[74]
We know that it occurs in *Clavellina* and in *Tubularia*; we may add
that it also happens in *Hydra*, and that in the flatworm *Planaria*
the pharynx, if it is too large for a piece that is cut out, may be
differentiated back and be replaced by a new pharynx, which is smaller.

[74] “Retro”-differentiation, of course, is not “Re”-differentiation
(“Umdifferenzierung,” see p. 111), though it may help it to occur.

It is not death and sloughing of parts that occurs in these cases,[75]
but a real process of active morphogenesis; not, however, a process
consisting in the production of visible manifoldness, but the opposite.
Loeb was the first to lay much stress upon this topic, and indeed, there
may appear a very strange problem in its wake: the problem, whether
*all* morphogenesis might be capable perhaps of going backwards under
certain conditions.

[75] Of course such a real decay of parts may happen in other cases.

It is important to note that in most[76] cases retro-differentiation
occurs in the service of restitution: it goes on wherever restitution
requires it. This fact alone would show that not very much could be
explained here by the discovery of modern chemistry, important as
it is, that one and the same “ferment” or “enzyme” may affect both
the composition and the decomposition of the same compound. We could
regard what is called “catalysis” solely as an agent in the service of
entelechy. But this point also will become clearer in another part of
the work.

[76] Certain cases of retro-differentiation occurring under conditions
of strict fasting will be described in a later chapter.

*C.* ADAPTATION

INTRODUCTORY REMARKS ON REGULATIONS IN GENERAL

We have finished our long account of individual morphogenesis proper.
If we look back upon the way we have traversed, and upon those topics
in particular which have yielded us the most important general results,
the material for the higher analysis which is to follow, it must
strike us, I think, that all these results relate to regulations.
In fact, it is “secondary” form-regulations, according to our
terminology, that we have been studying under the names of equifinality,
back-differentiation, restitution of the second order, and so on, and
our harmonious-equipotential systems have figured most largely in
processes of secondary form-regulations also. But even where that has
not been the case, as in the analysis of the potencies of the germ in
development proper, form-regulations of the other type have been our
subject, regulations of the primary or immanent kind, the connection
of normal morphogenetic events being regulatory in itself. It was not
the phenomenon of organic regulation as such that afforded us the
possibility of establishing our proof of the autonomy of morphogenesis:
that possibility was afforded us by the analysis of the distribution of
potencies; but upon this distribution regulation is based, and thus
we may be said to have studied some types of regulation more or less
indirectly when analysing potencies.

It therefore seems to me that we shall have hopes of a successful issue
to our inquiries, if we now, on passing to what is called the physiology
of the vegetative functions, proceed to focus our attention on the
concept of regulation as such. And that is what we shall do: on our
way through the whole field of physiology, we shall always stop at any
occurrence that has any sort of regulatory aspect, and shall always ask
ourselves what this feature has to teach us.

But let us first try to give a proper definition of our concept. We
shall understand by “regulation” any occurrence or group of occurrences
on a living organism which takes place after any disturbance of
its organisation or normal functional state, and which leads to a
reappearance of this organisation or this state, or at least to a
certain approach thereto. Organisation is disturbed by any actual
removal of parts; the functional state may be altered by any change
among the parts of the organism on the one hand, by any change of the
conditions of the medium on the other; for physiological functioning
is in permanent interaction with the medium. It is a consequence of
what we have said that any removal of parts also changes the functional
state of the organism, but nevertheless organisation is more than a mere
sum of reactions in functional life. All regulations of disturbances
of organisation may be called *restitutions*, while to regulations of
functional disturbances we shall apply the name *adaptations*. It is
with *adaptations* that we have to deal in the following.

Let us begin our studies of adaptations in a field which may justly
be called a connecting link between morphogenesis and physiology
proper, not yet wholly separated from the science of the organic form,
morphology.

1. MORPHOLOGICAL ADAPTATION

*Morphological adaptation* is a well-established fact, and I need only
mention the striking differences between the land and water form of
amphibious plants, or the differences between the same species of plants
in the Alps and in the plains, or the very different aspect of the arms
of an athlete and of an ascetic, to recall to your memory what is meant
by this term.

Morphological adaptation is no part of individual morphogenesis proper,
but occurs at the end of it; at least it never occurs previous to the
full individual life of an organism, previous to its true functional
life; for it relates to the functions of the complete organism.

THE LIMITS OF THE CONCEPT OF ADAPTATION

It is especially, though by no means exclusively, among plants that
morphological adaptation assumes its most marked forms; and this topic,
indeed, may very easily be understood if we remember that plant-life
is in the very closest permanent dependence on the medium, and that
this medium is liable to many changes and variations of all kinds.
In order to elucidate our problem, it therefore seems convenient to
restrict our considerations for a while to the study of plants. There
exist very many external formative stimuli in the morphogenesis of
vegetation: would it then be possible to regard every effect of such
an external formative stimulus as a real morphological adaptation?
No; for that would not meet the point. The general *harmony* of form
is indeed concerned if gravity forces roots to shoot forth below at a
spot where they can enter the ground, or if light induces branches and
leaves to originate at places where they can obtain it for assimilation;
but gravity and light themselves are mere formative stimuli--of the
localising type--in these instances, for they relate only to the
individual production of form, not to the functioning of already
existing form. We therefore are warned not to confuse the effects of
formative stimuli from without with real adaptive effects until we have
fully analysed the particular case.

We have drawn a sharp line between causes and means of morphogenesis,
applying the term “means” to those conditions of the morphogenetic
process which relate neither to the specificity nor to the localisation
of its constituents, though they are necessary for the accomplishment
of the process in the most thorough manner. Would it be possible to
connect our new concept of an adaptation with our well-established
concept of a means of morphogenesis in such a way that we might speak
of a morphological “adaptation” whenever any specific feature about
morphogenesis proves to be immediately dependent for its success on some
specific means, though it does not owe its localisation to that means
as its “cause”? It seems to me that such a view would also fall wide
of the mark. It is well known, for instance, that the flowers of many
plants never fully develop in the dark; light is necessary for their
morphogenesis. Is, therefore, their growth in the presence of light to
be called a morphological “adaptation” to light? Certainly not: they
simply *cannot* originate without light, because they require it for
some reason. It is precisely here that our conception of light as a
“means” of morphogenesis is most fully justified. There are many[77]
such cases; and there are still others of an apparently different
type, but proving the same. All pathological forms produced in plants
by animal parasites or by parasitic fungi could hardly be called
adaptations, but must be attributed to some abnormality of means or of
stimuli. It may be that the organism reacts as well as possible in these
cases, and that if it reacted otherwise it would die--we know absolutely
nothing about this question. But even then there would only be some sort
of regulation *in* the process of pathological morphogenesis, but *the
process* itself could hardly be called adaptive.

[77] Klebs has suppressed the reproductive phase of organisation
altogether, in fungi as well as in flowering plants, or has made it
occur abnormally early, merely by changing the “external conditions”
and by altering the “internal” ones correspondingly. There is hardly
anything like an adaptation in these cases, which, by the way, offer
certain difficulties to analysis, as the boundaries between “cause” and
“means” are not very sharp here.

So far we have only learned what is not to be regarded as morphological
adaptation. No response to external formative stimuli is in itself an
example of adaptation, nor are processes dependent for their existence
on any kind of condition or means to be called, simply because they are
dependent on them, adaptations to those agents. What then, after all, is
a morphological adaptation?

Let us remember what the word adaptation is really to mean in our
discussions: a state of functioning is adapted--a state of functioning
must therefore have been disturbed; but as functioning itself, at least
in plants, certainly stands in close relations to the medium, it follows
that all adaptations are in the last resort connected with those factors
of the medium which affect functioning. In being correctives to the
disturbances of functioning they become correctives to the disturbing
factors themselves.

But again, the question seems to arise whether these factors of the
medium, when they provoke an adaptation by some change that is followed
by functional disturbance, do so in the capacity of “causes” or of
“means,” and so it might seem that we have not gained very much so far
by our analysis. The reproach, however, would not be quite justified,
it seems to me: we indeed have gained a new sort of analytical concept,
in the realm of causal concepts in general, by clearly stating the
point that adaptations are related directly to functionality, and only
indirectly, through functionality, to external changes. By the aid of
this logical formulation we now are entitled to apply the term “cause,”
in our restricted sense of the word, to every change of the medium
which is followed by any sort of adaptation in regard *to itself*. Our
definition stated that a “cause” is any one of the sum of necessary
factors from without that accounts either for the localisation *or* for
*the specification* of the effect, and the definition holds very well in
this case. Indeed, the specification of the effect is determined *by*
the outside factor in every case of an adaptation *to* it, by the mere
*fact* of its being a specific adaptation to this specific factor.

We must not forget that in this chapter we are not studying real
individual morphogenesis as the realisation of what has been inherited,
but that at present we regard morphogenesis proper as an accomplished
fact. Morphogenesis proper has laid the general lines of organisation;
and now adaptation during the functional life, so to speak, imposes a
second kind of organisation upon the first. It is for that reason that
the meaning of the word “cause” is now becoming a little different from
what it was before.

In order to study a little more in detail what has been discovered
about morphological adaptation in animals and plants, let us separate
our materials into two groups, one of them embracing adaptations with
regard to functional changes from without, the other adaptations to
those functional changes which come from the very nature of functioning.
Almost all of our previous general considerations have applied to the
former group, with which we shall now proceed to deal.

ADAPTATIONS TO FUNCTIONAL CHANGES FROM WITHOUT[78]

[78] Compare Herbst, *Biol. Centralbl.* 15, 1895; and Detto, *Die
Theorie der direkten Anpassung*, Jena, 1904. A full account of the
literature will be found in these papers.

The differences between plants grown in very dry air, very moist air,
and water, respectively, are most distinctly seen in all the tissues
that assist in what is called transpiration, that is, the exchange of
water-vapour between the plant and the medium, but especially in the
epidermis and the conductive fibres, both of which are much stronger
in plants grown in the dry. Indeed, it seems from experiments that
transpiration is the most essential factor to which “adaptation” occurs
in amphibious plants, though the changes of the mechanical conditions
according to the medium also seem to have some sort of structural
effect. If plants stand very deeply in water, the conditions of
illumination, so important for assimilation in plants, may have been
altered, and therefore much of the structural change can be attributed
also to them. It is unimportant in our general question what is due to
one of these factors and what to the other. That there is a real sort
of adaptation cannot be doubtful; and the same is true, as experimental
observations of the last few years have shown, with regard to the
structural differences between so-called sun-leaves and shade-leaves
of plants grown in the air: it has been actually shown here that the
functional life of the former goes on better in the sun, of the latter
better in the shade.

It is very important to emphasise this point, as the adaptive character
of all sorts of structural differences in plants dependent on light
and on moisture has lately been denied, on the supposition that there
is only a stopping of organogenesis in the case of the more simple,
a continuance in the case of the more complicated modification, but
nothing else. Indeed, all morphological adaptation has been conceived
as only consisting in differences dependent upon the absence or the
presence of necessary means or causes of development, and as offering
no problem of its own. We have gained the right position from which
to oppose this argument, it seems to me, in our formula that all
adaptations do relate *not* directly *to* the agents of the medium,
but to changes of functional states induced *by* those agents; that
adaptations only *are* “adaptations” by being correctives to the
functional state.

There simply *is* an “adaptation” of structure in *such* a sense in all
the cases we have mentioned. We can say neither more nor less. Granted
that one of the outside factors which comes into account is merely a
necessary “means”: then why is the histological consequence of the
presence of the means an actual adaptation to it as far as its relation
to functioning is concerned--why is the consequence of its absence also
an adaptation to this absence in its relation to functioning? Why, to
complete the series, is the degree of the consequence of its presence an
adaptation to the degree of its presence?

All these relationships, which are so many facts, have been absolutely
overlooked by those who have been pleased to deny morphological
adaptation to functional changes from without.

To do full justice to them we may speak of “primary” regulative
adaptations in all the cases mentioned above, applying the word
“primary,” just as was done with regard to restitutions, to the fact
that there is some sort of regulation *in* the normal connection of
processes. We reserve the title of “secondary adaptations” for cases
such as those described, for instance, by Vöchting,[79] where not
merely one and the same tissue originates adaptively with regard to the
degree of its normal functioning, but where a profound disturbance
of all functioning connections, due to the removal of portions of the
organisation, is followed by histological changes at absolutely abnormal
localities; that is, where a real change of the *kind* of functioning
is the consequence of the adaptation. It, of course, will be found very
difficult to discriminate such phenomena from real restitutions, though
logically there exists a very sharp line between them.

[79] Vöchting (*Jahrb. wiss. Bot.* 34, 1899) forced the bulbs of
plants to become parts of the stem, and parts of the stem to form
bulbs; in both cases the most characteristic changes in histology
could be observed, being in part adaptations, but in part restitutions
of the proper type. (See also my *Organische Regulationen*, 1901, p.
84.) A true and simple instance of a “secondary adaptation” seems to
be furnished in a case described by Boirivant. In *Robinia* all the
leaflets of a leaf-stalk were cut off: the leaf-stalk itself then
changed its structure in order to assist assimilation, and also formed
real stomata.

A few more concrete instances may now close this account of adaptation
to functional changes coming from without. Though almost all the
adaptive characters in the aquatic forms of amphibious plants represent
a less complicated state of organisation than the corresponding
structures in their terrestrial forms, and therefore have wrongly
been regarded as simply due to a stopping of morphogenesis for want
of necessary means, yet there are a few of them that are positive
complications in comparison with the land-forms: the so-called
aërenchyme, especially well developed in the water-form of *Jussiaea*
is such an instance. This tissue stands in the direct service of
respiration, which is more difficult to be accomplished under water than
ordinarily, and represents a true adaptation to the altered function.

Among animals there is only one well-studied instance of our first type
of adaptive morphological characters. *Salamandra atra*, the black
salamander, a species which only inhabits regions at least two thousand
feet above sea-level, does not bring forth its young until metamorphosis
has taken place. The larvae, however, may be removed from the mother’s
body at an earlier stage and forced to complete their development in
water. Under these circumstances, as was shown in an excellent memoir
by Kammerer,[80] they will change the whole histological type of their
gills and skin in order to meet the new functional conditions. The
change of the conditions of functioning is very severe here, for whereas
the gills had served for nutrition and respiration in the uterus--by
a process of endosmosis--they now serve for respiration only, and, of
course, are surrounded by quite an abnormal chemical medium.

[80] *Arch. Entw. Mech.* 17, 1904.

TRUE FUNCTIONAL ADAPTATION[81]

[81] Roux, *Gesammelte Abhandlungen*, vol. i. 1895; in particular, *Der
Kampf der Teile im Organismus*, Leipzig, 1881.

But all other cases of morphological adaptation among animals, and
several in the vegetable kingdom too, belong to our second group of
these phenomena, which in our analytical discussion we have called
adaptations to functional changes that result from the very nature
of functioning, and which we shall now call by their ordinary name,
“functional adaptation.”

It was Roux who first saw the importance of this kind of organic
regulation and thought it well to give it a distinguishing name. *By
functioning the organisation of organic tissues becomes better adapted
for functioning.* These words describe better than any others what
happens. It is well known that the muscles get stronger and stronger the
more they are used, and that the same holds for glands, for connective
tissue, etc. But in these cases only quantitative changes come into
account. We meet with functional adaptations of a much more complicated
and important kind, when for instance, as shown by Babák,[82] the
intestine of tadpoles changes enormously in length and thickness
according as they receive animal or vegetable food, being nearly twice
as long in the second case. Besides this the so-called mechanical
adaptations are of the greatest interest.

[82] *Arch. Entw. Mech.* 21, 1906. By a very detailed comparative study
Babák was able to prove that it is the plant proteids to which the
effect of vegetable food is chiefly due; thus we have an adaptation
to digestibility. Mechanical circumstances are only of secondary
importance. (See also Yung.)

It has long been known, especially from the discoveries of Schwendener,
Julius Wolff, and Roux, that all tissues whose function it is to resist
mechanical pressure or mechanical tension possess a minute histological
structure specially suitable to their requirements. This is most
markedly exhibited in the stem of plants, in the tail of the dolphin, in
the arrangements of the lime lamellae in all bones of vertebrates. All
these structures, indeed, are such as an engineer would have made them
who knew the sort of mechanical conditions they would be called upon to
encounter. Of course all these sorts of mechanically adapted structures
are far from being “mechanically explained,” as the verbal expression
might perhaps be taken to indicate, and as indeed has sometimes been the
opinion of uncritical authors. The structures exist *for* mechanics,
not *by* it. And, on the other hand, all these structures, which we
have called mechanically “adapted” ones, are far from being mechanical
“adaptations,” in our meaning of the word, simply because they are
“adapted.” Many of them indeed exist previous to any functioning, they
are for the most part truly inherited, if for once we may make use of
that ambiguous word.

But, the merely descriptive facts of mechanical adaptedness having been
ascertained, there have now been discovered real mechanical processes
of adaptations also. They occur among the statical tissues of plants,
though not in that very high degree which sometimes has been assumed
to exist; they also occur in a very high perfection in the connective
tissue, in the muscles and in the bone tissue of vertebrates. Here
indeed it has proved possible to change the specific structure of the
tissue by changing the mechanical conditions which were to be withstood,
and it is in cases of healing of broken bones that these phenomena have
acquired a very great importance, both theoretically and practically:
the new joints also, which may arise by force of circumstances,
correspond mechanically to their newly created mechanical function.

So far a short review of the facts of “functionelle Anpassung.” They
seem to prove that there does exist a morphological adaptation to
functional changes which result from the very nature of functioning. In
fact, the actual state of all functioning tissue, the intensity of its
state of existence, if you care to say so, may be said to be due to the
functioning itself: the so-called atrophy by inactivity being only one
extreme of a very long line of correspondences.[83]

[83] Atrophy of muscles by inactivity is not to be confused with atrophy
by cutting the motor nerve; the latter is very much more complete.

We now, of course, have to ask ourselves if any more intimate analysis
of these facts is possible, and indeed we easily discover that here
also, as in the first of our groups of morphological adaptations,
there are always single definite agents of the medium, which might be
called “causes” or “means” of the adaptive effects, the word “medium”
being taken as embracing everything that is external to the reacting
cells. But of course also here the demonstration of single formative
agents does not detract in the least from the adaptive character of
the reaction itself. So we may say, perhaps, that localised pressure
is the formative stimulus for the secretion of skeleton substance at a
particular point of the bone tissue, or of the fibres of the connective
tissue; the merely quantitative adaptations of muscles might even
allow of a still more simple explanation.[84] But adaptations remain
adaptations in spite of that; even if they only deserve the name of
“primary” regulations.

[84] Loeb has advocated the view that the “adaptive” growth of working
muscles is simply due to the presence of a greater number of molecules
in their protoplasm, muscular activity being generated by a process of
chemical decomposition.

THEORETICAL CONCLUSIONS

We have stated in the analytical introduction to this chapter and
elsewhere, that functional changes, which lead to morphological
adaptations of both of our groups, may arise not only from changes of
factors in the medium, but also from a removal of parts. As such removal
is generally followed by restitution also, it is clear that restitutions
and adaptations very often may go hand in hand, as is most strikingly
shown in a fine series of experiments carried out by Vöchting, which we
have already alluded to. Here again I should like to lay the greatest
stress upon the fact that, in spite of such actual connections,
restitutions and adaptations always have been separated from another
theoretically, and that the forms are never to be resolved into sums
of the latter. Such a view has been advocated by some recent authors,
especially by Klebs, Holmes, and Child:[85] it is refuted I think by the
simple fact that the first phase of every process of restitution, be it
regeneration proper or be it a sort of harmonious differentiation, goes
on without functioning at all, and only *for* future functioning.[86]

[85] What has been really *proved* to exist by the very careful studies
carried out by Child, is only certain cases of functional adaptation
to mechanical conditions of the strictest kind, and relating to the
general mobility only, but nothing more; such adaptations can be said to
accompany restitution. See, for instance, *Journ. exp. Zool.* 3, 1906,
where Child has given a summary of his theory.

[86] Even in Vöchting’s experiments (see page 174, note 1), in which
adaptations are mixed with true restitutions in the closest possible
manner, a few phenomena of the latter type could most clearly be
separated. The stimulus which called them forth must have been one of
the hypothetic sort alluded to in a former chapter (see page 113). The
best instances of true restitutions were offered in those cases, where,
after the removal of all the bulbs, typical starch-storing cells were
formed without the presence of any starch.

And there has been advocated still another view in order to amplify
the sphere of adaptation: all individual morphogenesis, not only
restitution, is adaptation, it has been said. In its strictest form
such an opinion of course would simply be nonsense: even specific
adaptive structures, such as those of bones, we have seen to originate
in ontogeny previous to all specific functions, though for the help
of them, to say nothing of the processes of the mere outlining of
organisation during cleavage and gastrulation. But they are “inherited”
adaptations, it has been answered to such objections. To this remark we
shall reply in another chapter. It is enough to state at present that
there *is* a certain kind of, so to speak, architectonic morphogenesis,
both typical and restitutive, previous to specific functioning
altogether.

If now we try to resume the most general results from the whole field
of morphological adaptations, with the special purpose of obtaining new
material for our further philosophical analysis, we have reluctantly to
confess that, at present at least, it does not seem possible to gather
any new real proof of life-autonomy, of “vitalism,” from these facts,
though of course also no proof against it.

We have stated that there is in every case of both our types of
adaptive events a correspondence between the degree of the factor
to which adaptation occurs, and the degree of the adaptive effect.
We here may speak of an *answering* between cause and effect with
regard to adaptation, and so perhaps it may seem as if the concept of
an “answering reaction” (“Antwortsreaktion”), which was introduced
into science by Goltz[87] and which is to play a great part in our
discussions of next summer, may come into account: but in our present
cases “answering” only exists between a simple cause and a simple effect
and relates almost only to quantity and locality. There is therefore
lacking the most important feature, which, as will be seen, would have
made the new concept of value.

[87] *Beiträge zur Lehre von den Functionen der Nervencentren des
Frosches*, Berlin, 1869.

We only, I believe, can state the fact that there *are* relations
between morphogenetic causes and effects which *are* adaptations, that
functional disturbances or changes are followed by single histogenetic
reactions from the organism, which are compensations of its disturbed or
changed functional state. We are speaking of facts here, of very strange
ones indeed. But I feel unable to formulate a real proof against all
sorts of mechanism out of these facts: there *might* be a machine, to
which all is due in a pre-established way. Of course we should hardly
regard such a machine as very probable, after we have seen that it
*cannot* exist in other fields of morphogenesis. But we are searching
for a new and independent proof; and that is indeed not to be found
here.[88]

[88] The “secondary adaptations” observed by Vöchting are too
complicated and too much mingled with restitutions to allow any definite
analysis of the fact of the “secondary adaptation” as such.

At present it must be taken as one of the fundamental *facts* of the
organogenetic harmony, that the cells of functioning tissues do possess
the faculty of reacting to factors which have changed the state of
functioning, in a way which normalises this state histologically. And
it is a fact also that even cells, which are not yet functioning but
are in the so-called embryonic or indifferent condition contributing to
the physiological completion of the tissue, react to factors embracing
new functional conditions of the whole in a manner which leads to an
adaptation of that whole to those conditions.

This is a very important point in almost all morphological adaptation,
whether corresponding to functional changes from without or resulting
from the very nature of functioning. In fact, such cells as have already
finished their histogenesis are, as a rule, only capable of changing
their size adaptively, but are not able to divide into daughter-cells
or to change their histological qualities fundamentally; in technical
terms, they can only assist “hypertrophy” but not “hyperplasia.” Any
adaptive change of a tissue therefore, that implies an increase in the
number of cellular elements or a real process of histogenesis, has to
start from “indifferent” cells, that is to say, cells that are *not yet*
functioning in the form that is typical of the tissue in question; and,
strange to say, these “embryonic” cells--*i.e.* the “cambium” in higher
plants and many kinds of cells in animals--*can* do what the functional
state requires. It is to be hoped that future investigations will lay a
greater stress upon this very important feature of all adaptation.

2. PHYSIOLOGICAL ADAPTATION[89]

[89] General literature: Fröhlich, *Das natürliche
Zweckmüssigkeitsprincip in seiner Bedeutung für Krankheit und Heilung*,
1894. Driesch, *Die organischen Regulationen*, 1901. A. Tschermak, “Das
Anpassungsproblem in der Physiologie der Gegenwart,” in a collection
of papers in honour of J. P. Pawlow, St. Petersburg, 1904. Bieganski,
“Ueber die Zweckmässigkeit in den pathologischen Erscheinungen,” *Annal.
d. Naturphil.* 5, 1906. Among the general text-books of physiology those
by Pfeffer (*Pflanzenphysiologie*, 1897-1904) and von Bunge (*Lehrbuch
d. Phys. d. Menschen*, 1901) are the fullest on the subject of
“regulations.” See also different papers on general pathology by Ribbert.

It is but a step from morphological adaptations to adaptations in
physiology proper. The only difference between regulations of the
first type and those which occur in mere functioning is, that the
resulting products of the regulation are of definite shape and therefore
distinctly visible in the first case, while they are not distinctly
visible as formed materials but are merely marked by changes in chemical
or physical composition in the latter.

Metabolism, it must never be forgotten, is the general scheme within
which all the processes of life in a given living organism go on; but
metabolism means nothing else, at least if we use the word in its
descriptive and unpretentious meaning, than change in the physical
or chemical characteristics of the single constituents of that
organism. In saying this, we affirm nothing about the physical or
chemical nature of the actual processes leading to those physical or
chemical characteristics, and by no means are these “processes” *a
priori* regarded as being physical or chemical *themselves*: indeed,
we have learned that in one large field, in the differentiation of
our harmonious systems they certainly are not. Now, if the metabolism
does not end in any change of visible form, then true physiological
processes, or more particularly physiological regulations, are going on
before us. But we are dealing with morphogenetic events or regulations,
if the result of metabolism is marked by any change in the constituents
of form. This however may depend on rather secondary differences as to
the nature of regulation itself, and any kind of metabolism may really
be of the regulatory type, whether we actually see its result as a
constituent of form, *e.g.* owing to the production of some insoluble
compound, or whether we do not.

I do not mean to say that these are the only differences between mere
physiological activities or regulations and organogenesis proper, as an
originating of typical form-combination; but if we regard, as we do in
this chapter, the given organisation of a living being as a substratum
of its functional life, morphological and physiological adaptations are
indeed of almost the same logical order.

We had best therefore begin our discussions with a recapitulation of
our problem. We are studying adaptations in functioning--that means we
want to know how the organism behaves with regard to any change which
may take place in its functional state. We apply the term regulation,
or in particular adaptation, to any kind of reaction on the part of the
organism which re-establishes the normal state of functioning, and we
now want to learn to what degree such adaptations exist in the field of
physiology.

SPECIFIC ADAPTEDNESS *NOT* “ADAPTATION”

It is important to keep well in mind our strictly formulated theme, as
by doing so we shall be able to exclude at once from our materials a
large group of phenomena which occasionally have been called regulations
by physiological authors, but which, in fact, are not of the adaptation
type and therefore cannot be said to afford those problems which
possibly might have been expected. Typical peculiarities in functional
life cannot be called “regulations” for this very reason. If, for
instance, the organism selects specific amounts of specific kinds of
organic food or of salts out of the combinations of salts or organic
food normally offered to it in the medium, as indeed is most typically
shown for instance by the roots of plants, there cannot be said to occur
a “regulation” or “adaptation” with regard to the permeability of the
cell, nor is it strictly a case of “regulation,” if so-called selective
qualities are discovered in the processes of secretion, say of the
epithelium of the kidney.

All these facts are typical and specific peculiarities in functioning
which are duly to be expected, where a very typical and specific
organisation of the most elaborated kind exists. Indeed, after studying
such an organisation we must not be astonished that functions in
organisms follow lines which certainly they would not have taken without
it. Take the fact which is quoted very often, that the migration of
compounds or of ions in the organisms can happen quite contrary to all
the laws of osmosis, from the less concentrated to the more concentrated
side of a so-called “membrane.” There *is* no simple “membrane” in the
organism, but a complicated organisation of an almost unknown character
takes its place, and nothing, indeed, is against the assumption that
this organisation may include factors which actually drive ions or
compounds to the side of higher concentration, which indeed drive them
by “doing work,” if we like to speak in terms of energy; and these
factors included in organisation may very well be of a true physical or
chemical nature.[90]

[90] According to investigations of the last two years, the physics of
colloids seems to play as important a part in physiology as osmosis
does; we here meet “means” of functioning just as we have already had
“means” of organogenesis.

I lay great stress upon these statements, as I should like to be as
careful as possible in the admission of anything like a “proof” of
vitalism. It was want of scientific criticism and rigid logic that
discredited the old vitalism; we must render our work as difficult as
possible to ourselves, we must hold the so-called “machine theory” of
life as long as possible, we must hold it until we are really forced to
give it up.

In a more general form we now can sum up our discussion by saying: There
never are adaptations in physiology, requiring any special analysis,
where there are only complications or even apparent deviations from the
purely physico-chemical type of events which are, so to say, statical,
*i.e.* fixed in quantity or quality, however peculiar or typically
complicated they may be; all such peculiarities indeed, may properly
be called “adapted,” that is to say, very well fitted to perform a
specific part in the service of normal general functioning, and they
are “adapted” to their part by virtue of a certain “adaptedness” of the
organisation; but they are not “adaptations” in any sense of the word.

PRIMARY AND SECONDARY ADAPTATIONS IN PHYSIOLOGY

We approach the subject of true adaptations, that is, of adapting
processes, as soon as any kind of variation in functioning occurs which
corresponds to a variation of any factor of the medium in the widest
sense. But even here our work is by no means done by simply showing
such a correspondence of outer and inner variations. We know very well
already, from our former studies, that now we are faced by a further
problem, that we are faced by the question whether we have to deal with
simple primary kinds of adaptations or with the far more important
secondary ones.

As the discrimination between primary and secondary regulations proves
indeed to be of first-rate importance, you will allow me, I hope, to
summarise our chief analytical statements regarding them in a most
general form. We call primary regulatory any kind of morphogenetic or
functional performance, which, by its very intimate nature, always
serves to keep the whole of organisation or of functions in its normal
state. We call secondary regulations all features in the whole of
morphogenesis or of functioning which serve to re-establish the normal
state after disturbances along lines which are outside the realm of
so-called normality. This analytical discrimination will help us very
much to a proper understanding of physiology. But before we turn to
apply our definitions to actual facts, another preliminary problem has
to be solved.

ON CERTAIN PRE-REQUISITES OF ADAPTATIONS IN GENERAL

We are thinking of the general and important question, what types of
adaptations may be expected in the field of physiology and whether
there may be certain classes of regulatory events which possibly might
be expected to occur in the organism on *a priori* grounds, but which,
nevertheless, are to be regarded as impossible after a more intimate
analysis of its nature, even at the very beginning? Or, in other words,
to what kinds of changes of the medium will an organism be found able or
unable to adapt itself?

We know that the *state of functioning* must be altered in order to call
forth any sort of adaptation at all. Now, there can be no doubt that *a
priori* it would seem to be very useful for the organism, if it never
would let enter into its blood, lymph, etc., be it through the skin or
through the intestine, any chemical compound that would prove to be
a poison afterwards. In fact, a man, judging on the principle of the
general usefulness of all the phenomena of the living, might suppose
that there would exist a sort of adaptation against all poisons to the
extent that they would never be allowed to enter the real interior of
the body. We know that such reasoning would be incorrect. But we also
can understand, I suppose, that an *a priori* analysis of a more careful
kind would have reasoned differently. How could the functional state
of the organism be changed, and how, therefore, could adaptation be
called forth by any factor of the medium which had not yet entered the
organism, but was only about to enter it? Not at all therefore is such
a regulation to be expected as we have sketched; if there is to be any
adaptation to poisons, it only can occur after the poison has really
acted in some way, and in this case we shall indeed find regulations.

You may perhaps regard this discussion as a little too academical
and hair-splitting, but here again it was for the sake of ensuring a
perfectly sound foundation of our chief principles that I undertook it.
Very often, indeed, the question has been raised by the defenders of a
mechanistic theory of life, Why then did the organisms not reject all
poisons from the very beginning? We now may reply to that only--how
*could* they do so? How could they “know” what is a poison and what is
not, unless they had experienced it?--if we are allowed for a moment to
use very anthropomorphistic language.

We repeat, therefore, that the functional conditions of the organism
must have been actually changed in order that an adaptation may occur.
Nothing is more essential to a clear understanding of our problems than
to keep fully in mind the exact sense of this definition.

ON CERTAIN GROUPS OF PRIMARY PHYSIOLOGICAL ADAPTATIONS

*General Remarks on Irritability.*--Turning now to more special groups
of problems concerning physiological adaptations, let us begin with the
primary class of them, and let us first say a few words on a subject
which occasionally has been regarded as the basis of physiological
regulation in general. I refer to a most important fact in the general
physiology of irritability. Irritability of any kind is known to be
re-established, after it has been disturbed by the process of reacting
to the stimulus, and in certain cases, in which two different--or rather
two opposite--kinds of reactions are possible on the same substratum,
which increase with regard to one process whilst decreasing at the same
time with regard to the other. The irritability of the muscle or of the
leaves of *Mimosa* is a very good instance of the first case, whilst the
second more complicated one cannot be illustrated better than by what
all experience has taught us about the irritability of the retina. The
retina is more irritable by green rays and less by red ones the more
it has been stimulated by the latter, and more sensitive to light in
general the more it has been exposed to darkness; and something very
similar is true, for instance, as regards phototactic irritability in
plants, all these phenomena being in relation to the so-called law of
Weber.[91]

[91] I only mention here that certain modern psychologists have assigned
the true law of Weber to the sphere of judgment and not of sensation. If
applied to objective reactions only, in their dependence on objective
stimuli, it, of course, becomes less ambiguous, and may, in a certain
sense, be said to measure “acclimatisation” with regard to the stimulus
in question. The mathematical analogy of the law of Weber to the most
fundamental law of chemical dynamics seems very important.

As to “acclimatisation” in the more usual meaning of the word, with
regard to a change of the general faculty of resisting certain agents
of the medium, “immunity” proper is to form a special paragraph of what
follows, and to “acclimatisation” towards different degrees of salinity
(in algae or fishes) some special remarks will also be devoted on a
proper occasion. There remains only “acclimatisation” to different
temperatures; but on this topic not much more than the fact is known
(see Davenport, *Arch. f. Entw. Mech.* 2, p. 227). “Acclimatisation”
does not allow of a sharp general definition; it may be the result of
very *different* kinds of adaptations in our sense of the word.

It seems to me that there would be little difficulty in harmonising the
phenomenon of the inversion of irritability with the so-called principle
of the “action of masses” and with the laws of certain “reversible”
processes well known in chemistry. As to the simple fact of the
re-establishment of irritability after stimulation has occurred, or,
in certain other cases, the fact that in spite of permanent stimulation
irritability seems to exist permanently also, physical analogies or even
explanations might very well be found.[92]

[92] I should think that the problem of the re-establishment of
irritability, in principle at least, arises even when there is not a
trace of so-called “fatigue” or of a “refractory period.” The process
of restoring may be so rapid as not to be noticeable, nevertheless some
sort of restoring is to be postulated. We may say the “irritability” of
an elastic ball is re-established by its elasticity. A certain analogy
to this case may perhaps be found in the muscle. But the irritability
of nerves with respect to nervous conduction, and of glands with
respect to secretion, or of the articulations of *Mimosa* may be well
understood, hypothetically at least, if we assume that the ordinary
course of metabolic events is apt in itself to lead to a certain state
or condition of the organs in question upon which their irritability
is based. Certain general conditions of functioning, as for instance
the presence of oxygen for the contraction of the muscle, would better
be looked upon as necessary “means” of functioning than as being part
of irritability as such. “Fatigue,” of course, may also be due to
the absence of such “means” or to abnormal conditions originated by
functioning itself.

If now we ask whether there is anything like an adaptation appearing in
the general characteristics of irritation and irritability, it seems to
me that we may answer the question in an affirmative manner, as far as
primary regulation comes into account. We, certainly, have not studied
any abnormal regulatory lines of general functioning, we only have
studied general functioning itself; but, indeed, there was a certain
sort of regulation *in* functioning. Of course, by showing that one
of the most general features of all functioning is primary-regulatory
in itself, we do not deny the possibility of many specific functions
in which real secondary regulations actually do exist. Nothing indeed
is asserted about the *specific* character of functioning in its
different types, by proving that one of the *general* features of *all*
functioning may comparatively easily be understood. It seems to me that
this important logical point has not always received the attention it
deserved.

*The Regulation of Heat Production.*[93]--Having finished our
introductory remarks we now turn to the proper study of special
physiological functioning with regard to its adaptive side, and begin
with the most simple cases.

[93] Rubner, *Die Gesetze des Energieverbrauches bei der Ernährung*,
Leipzig u. Wein, 1902.

The so-called “regulation of heat” in warm-blooded vertebrates is an
instance of a special function which can be said to be regulatory in
itself. There exists a normal blood heat for each species, which is
maintained no matter whether the temperature of the medium rise or fall.
It might seem at first as if in this case there were a little more
of an adaptive regulation than only its well-known primary type; no
reversion, one might say, of the direction of one and the same process
occurs in the regulation of heat production, but one kind of process
is called into action if it is necessary to raise the temperature, and
another whenever it is necessary to lower it. Even in the dilatation
and constriction of capillary vessels there are different nerves
serving for each operation respectively, and far more important are the
increasing of transpiration for cooling, the increasing of combustion
for heating--two radically different processes. But, nevertheless, there
is a certain unity in these processes, in so far as a specific locality
of the brain has been proved to be the “centre” of them all; it is to
this centre of course that the analysis of heat production considered as
a kind of regulation or adaptation must be directed. Such an ultimate
analysis, it seems to me, would have to classify heat regulation under
the primary type of adaptations in physiology without any restriction.
The centre acts in one sense or in the other, if stimulated by any
temperature beyond a very limited range, and it is in the action of the
centre that the “regulation” of heat consists.[94]

[94] The phenomenon of fever we leave out of account here; it is
regarded by some as regulation, by others as a disturbance of heat
regulation. Of course, if the first view should ever prove to be the
right one, fever might be classified among the real regulations of the
secondary type.

*Primary Regulations in the Transport of Materials and Certain Phenomena
of Osmotic Pressure.*--Very similar phenomena of regulation are present
in many processes concerned in the whole of metabolism. Let us consider
for a moment the migration of materials in plants. Whenever any compound
is used at a certain place, a permanent afflux of this compound to
that place sets in from all possible directions. No doubt this is a
“regulation,” but it is also the function itself, and besides that,
a very simple function based almost entirely on well-known laws of
physical chemistry. And in other cases, as in the ascent of water to
the highest tops of our trees, which purely physical forces are said to
be insufficient to explain, we can appeal to the unknown organisation
of many cells, and there is nothing to prevent our attributing to these
cells certain functions which are, if you like to say so, regulatory
in themselves. Among other facts of so-called regulations there is the
stopping of metabolic processes by an accumulation of their products:
as, for instance, the transformation of starch into sugar is stopped,
if the sugar is not carried away. Of course that is a regulation, but
it again is an intrinsic one, and it is one of the characteristics of
reversible chemical processes to be stopped in that way. I know very
well that in this particular case a certain complication is added by
the fact that it is a so-called ferment, the diastase, which promotes
the transformation of starch into cane-sugar, and that this ferment is
actively produced by the organism: but even its production would not
prove that any real kind of secondary regulation exists here, if nothing
more were known about such an active production than this single case.

In a special series of experiments almost all carried out in Wilhelm
Pfeffer’s botanical laboratory at Leipzig, an attempt has been made
to discover in what manner the cells of plants are able to withstand
very high abnormalities of the osmotic pressure of the medium--that is
to say, very great changes in the amount of its salinity. That many,
particularly the lower plants, are able to stand such changes had been
ascertained already by the careful examinations of Eschenhagen; but
recent years have given us a more profound insight into what happens.
Von Mayenburg[95] has found that sundry of the species of *Aspergillus*,
the common mould, are able to live in very highly concentrated solutions
of several salts (KNO_3 and Na_2SO_4). They were found to regulate
their osmotic pressure not by taking in the salts themselves, but by
raising the osmotic pressure of their own cell sap, producing a certain
amount of osmotically active substances, probably carbohydrates. If
in this case it were possible to assume that the osmotic pressure of
the medium were the real stimulus for the production of the osmotic
substances in the cell, stimulus and production both corresponding
in their degree, we should be entitled to speak of a primary though
physiological[96] regulation only; and it seems to me that despite the
discoveries of Nathansohn that certain algae and cells of higher plants
are able to change the permeability of their surfaces in a way which
regulates the distribution of single salts or ions in the sap of their
cells without any regard to pure osmotic equilibrium, such a simple
explanation might be possible.[97]

[95] *Jahrb. wiss. Bot.* 36, 1901.

[96] Carbohydrates cannot be ionised, and therefore there is no doubt
that in von Mayenburg’s experiments the organism itself is actively
at work. As to compounds liable to ionisation, it has been noticed by
Maillard that a certain regulatory character is contained simply in the
physical fact that the degree of ionisation changes with concentration:
decrease of concentration for instance would be followed by an increase
of ionisation, and so the osmotic pressure may be preserved (*C. rend.
Soc. Biol.* 53, 1901, p. 880).

[97] In the different experiments of Nathansohn (*Jahrb. wiss. Bot.*
38, 1902, and 39, 1903) the salinity of the medium was changed in such
a way that there was in each case either an abnormal increase or an
abnormal decrease in the concentration of one single ion necessary
for metabolism. The cell was found to stand these abnormal changes in
such a way that in the case of the increase of the concentration of
the medium it did not allow more than a certain amount of the ion in
question to come in, and that in the case of the decrease it did not
allow more than a certain quantity of the ion to go out. It thus seems
as if the permeability of the surface were adjusted to a certain minimum
and to a certain maximum of every single ion or salt, the permeability
being stopped from within to without, whenever the minimum, and from
without to within, whenever the maximum is reached in the cell sap; both
irrespective of proper physical osmotic equilibrium (“Physiologisches
Gleichgewicht”). Thus, in fact, there only would be a case of primary
regulation, nothing more. It would all appear rather similar to what
occurs in the kidney. Of course we do not assert that our explanation is
right, but it is possible and is at the same time the most simple, and
it is our general practice always to prefer the most simple hypotheses.

There are many regulation phenomena connected with osmotic pressure
and permeability in animal physiology also, though at present they are
not worked out as fully as possible. The works of Frédéricq, J. Loeb,
Overton and Sumner[98] would have to be taken into account by any
one who wished to enter more deeply into these problems. We can only
mention here that permeability to water itself also plays its part, and
that, according to Overton’s experiments, it is a kind of solubility
of the media in the very substance of the cell surface on which all
permeability and its regulation depend.

[98] Many fishes are able to withstand great changes in the osmotic
pressure of sea-water; the osmotic pressure of their body fluids, though
never in a real physical equilibrium with the pressure of the medium,
nevertheless may vary whenever the abnormal conditions of the latter
exceed certain limits.

*Chromatic Regulations in Algae.*--The phenomena of osmotic pressure and
its regulation may be said to be the preliminaries of metabolism proper,
conditions necessary for it to take place. Now there is another branch
of such preliminaries to metabolism, in which the most interesting
regulation phenomena have been lately discovered. It is well known that
what is called assimilation in plants, that is, the formation of organic
compounds out of carbon dioxide (CO_2) and water, occurs only in
the light by means of certain pigments. This pigment is in all higher
plants and in many others the green chlorophyll, but it may be different
in certain species of algae, and can generally be said[99] to be of
the colour complementary to the colour of those rays which especially
are to be absorbed and to be used for assimilation. But here we have
“adaptedness,” not adaptation. It was in some species of primitive
algae, the *Oscillariae*, that Gaidukow[100] found a very interesting
instance of an active regulation in the formation of pigments. These
algae always assume a colour which corresponds to the accidental colour
of the rays of the medium and is complementary to it; they become green
in red light, yellow in blue light, and so on--that is, they always
actively take that sort of colouring which is the most suitable to
the actual case.[101] There indeed occurs a sort of complementary
photography in these algae; but, though adaptive, it could hardly be
said to exceed the limits of “primary phenomena.”

[99] See Stahl, *Naturw. Wochenschrift*, N. F. 5, 1906, No. 19.

[100] *Arch. Anat. Phys.*, Phys. Abt. Suppl., 1902.

[101] The adaptive phenomena discovered by Gaidukow depend upon a real
alteration in the formation of pigments. In the (primary) chromatic
adaptation of pupae of Lepidoptera with respect to the colour of
the ground they live upon, we only have the variable effects of
pre-established chromatophores (Poulton, *Phil. Trans. London*, 178 B,
1888; Merrifield, *Trans. Ent. Soc. London*, 1898). The same holds for
chromatic adaptations in crabs (Gamble and Keeble, *Quart. Journ. Micr.
Sci.* 43, 1900; Minkiewicz, *Arch. Zool. exp. et gén.* sér. 4, 7, notes,
1907).

*Metabolic Regulations.*--And now we enter the field of regulations in
metabolism itself. There are two kinds of outside factors of fundamental
importance for all metabolic processes: food is one, and oxygen is the
other. And metabolism as a whole is of two different aspects also:
it both serves for assimilation proper--that is, building up--and it
supplies the energy for driving the functional machine. It is clear
that food alone--together of course with the assimilating means of the
organism, can account for the first type of metabolism, while both food
and oxygen, or some sort of substitute for the latter, as in certain
bacteria, supply functional energy. Of course we are not entitled to say
that the importance of so-called oxidation or respiration is exhausted
by its energetic rôle: it certainly is not, for if it were, the organism
would only be stopped in its functions if deprived of oxygen but
would not die. It seems that certain substances always arise in the
metabolism, in the processes of decomposition, which have to be burnt up
in order not to become poisonous. But we shall return to the phenomena
of organic oxidation in another chapter of the book, and shall deal with
them from a more general point of view.[102]

[102] The theory of oxidation we have shortly sketched here was
developed in chapter B. 5, of my *Organische Regulationen*. Recent
discoveries of Winterstein’s (*Zeitschr. allg. Physiol.* 6, 1907)
have given the strongest support to my hypothetic statements, and, in
fact, can be said to have brought the doctrine of organic oxidation
to a critical point. There can be no doubt that oxygen not only plays
the “antipoisonous” rôle I had assigned to it, but that it is not
even of such great importance for the supply of functional energy as
former times had assumed. No doubt it serves to drive the functional
machine, but decomposition of certain chemical constituents of the
organism serves this purpose even more. The latter does so in the most
fundamental and original manner, so to speak, whilst oxidation only
burns up its products. Almost all elemental functions, in nerve-tissue
at least, go on very well in the absence of oxygen, provided that
certain “poisonous” substances, resulting from this anaërobic
metabolism, are constantly removed. In normal conditions that is
done by oxygen, and in doing so oxygen certainly assists the supply
of energy, but it does not furnish the whole of it. The difference
between so-called “aërobic” and “anaërobic” life almost completely
disappears under such a view, and many so-called “regulations,” of
course, disappear at the same time; there is no more “intramolecular
respiration.”

Let us now try to take a short survey of all the regulations discovered
relating to the substitution of one kind of food for another. We have
said that food serves in the first place as building material, in the
second place as fuel. It only deserves brief mention that, as all recent
investigations have shown, fats, carbohydrates, and albumen are equally
well able to serve as fuel.[103]

[103] But nevertheless albumen is not to be replaced altogether in
vertebrates by fat or carbohydrate; it probably serves some special
function besides combustion, even in the adult.

It is in the state of fasting, *i.e.* in the case of a real absence of
*all* nourishing materials, that the organism has proved to be capable
of regulations of the most marked nature, with regard to the combustion
of its own materials. Respiration, we know, must go on if death is to
be avoided, and now indeed it has been found that this process attacks
the different tissues of the organism subjected to fasting in such an
order that, after the combustion of the reserves, the most unimportant
tissues with regard to life in general are destroyed first, the most
important ones last. Thus in vertebrates the nerve cells and the heart
are preserved as long as possible; in infusoria it is the nucleus; in
flatworms, as the very careful studies of E. Schultz[104] have lately
shown, it is the nerve cells and the sexual cells which longest resist
destruction, whilst almost all the rest of the organisation of these
animals may disappear. I should not say that we can do very much with
these facts at present in our theoretical discussion, but they are
certainly witness of very astonishing adaptive powers.[105]

[104] *Arch. Entw. Mech.* 18, 1904.

[105] To a physiological friend of mine I owe the suggestion that it is
the permanently functioning tissues which stand hunger better than the
others, at least if the sexual cells might be regarded as capable of
a *sécrétion interne* in all cases. Then the adaptations in the state
of hunger might be said to be reduced in some degree to “functional
adaptation.” But it must remain an open question, it seems to me,
whether such a view may indeed hold in the face of the facts observed in
*Planaria* and infusorians.

We now turn to study the cases of a compensation of nourishments
serving for the real building up of the organism. Albumen, we know, is
absolutely indispensable for animals, even for adults, though nothing is
known about the purpose it serves in the latter; its place can be taken
of course by those less complicated compounds which result from its
first decomposition, effected by pepsin and trypsin, but nothing else
will do. The salts of sea-water, according to Herbst’s experiments, may
only vary to a very small degree if the development of marine animals
is to go on well; potassium may be replaced by caesium or rubidium,
and that is all. Much the same is true of the salts necessary to
plants. It will not surprise us very much to hear that algae can also
be successfully fed with the potassium salts of organic compounds, and
higher plants with acid amides or glucoses instead of carbonic acid, as
those products are normal steps in their assimilation; and it may also
be fairly easily understood that nitrogen can be offered in organic form
instead of as a nitrate.

It was in the group of fungi that really important adaptations with
regard to the proper form-producing alimentation were first discovered,
and these are of a very complicated kind indeed. Fungi are known to
be satisfied with one single organic compound instead of the group of
three--fat, carbohydrate and albumen--necessary for animals. Now Pfeffer
showed that the most different and indeed very abnormal compounds were
able to bring his subjects to a perfect growth and morphogenesis; and,
moreover, he found that, if several kinds of such food were offered
together, they were consumed quite indifferently as to their chemical
constitution, but only with regard to their nutritive value: that sort
of food which had produced a better growth than another when both
were offered separately was found to save the latter from consumption
whenever both were offered together.

Here we are faced by one of the most typical cases of regulations in
metabolic physiology: the organism is able to decompose compounds of
the most different constitution, which have never been offered to it
before; but nevertheless, it must remain an open question whether real
“secondary” regulation has occurred, as nothing is known in detail about
the single steps of metabolism in these fungi. There *might* be some
ferments equally able to destroy different classes of compounds,[106]
and that the most nutritive compound is used up first *may* be a
question of physico-chemical equilibrium.

[106] In all cases where fungi of the same species are able to live on
different hosts, that is, to penetrate membranes of a different chemical
character, a similar objection as to the “secondary” type of such a
regulation may be made.

That is almost all[107] that is actually known of adaptation with regard
to the use of an abnormal food supply. Though important, it cannot be
said to be very much. But could we expect very numerous regulations
here at all after what we laid down in a former paragraph about the
possibilities of adaptive regulation in general? The functional state
must have been altered in order that such regulations may occur. Now
there is no doubt that this state may be really altered only if an
abnormal food has first been taken in altogether by the cell-protoplasm
of the body-surfaces, but never if it has only entered the cavity of the
intestine, which, strictly speaking, is a part of the exterior medium.
Fungi indeed not only take in the abnormal food, but also know what
to do with it, but all animals are obliged to treat first with their
chemical secretions what happens to be present in their intestine, in
order that it may be taken up by their living cells, and one hardly
can wonder that these secretions are only formed in correspondence to
a limited number of outside stimuli. In fact, as soon as we look upon
what adaptive or regulatory work happens in metabolism *inside* the body
interior, we meet, even in animals, regulations of a far more developed
type.

[107] The discovery of Weinland that adult dogs are able to produce
“lactase” in their pancreas, whenever they are fed, quite abnormally,
with milk-sugar, has recently been said to be vitiated by an analytical
mistake.

Discoveries of the last few years have taught us that almost all
metabolic processes in the organism, including oxidation, are carried
out by the aid of special materials, the so-called enzymes or
ferments. These are known to exist in the most different forms even in
the inorganic world. They are simply chemical compounds, of specific
types, that bring about chemical reactions between two other chemical
materials, which in their absence would either not go on at all or would
go on very slowly. We cannot enter here into the much disputed chemical
theory of what is called “catalysis”: we can only say that there is no
objection to our regarding almost all metabolic processes inside the
organism as due to the intervention of ferments or catalytic materials,
and that the only difference between inorganic and organic ferments is
the very complicated character of the latter and the very high degree of
their specification.

Such a statement, of course, does not say that all metabolism has proved
to be of a chemical nature: the *action* of the ferment when produced
is chemical, but we do not know at all *how* the ferment is produced;
we only know that a high degree of active regulation is shown in this
production. In fact, it has been proved in some cases, and probably will
be proved in a great many more in the near future, that all metabolic
ferments, whether they promote oxidation or assimilation proper or
chemical decomposition, are produced in a regulatory manner with regard
to the specific compound to be dissociated or to be built up. In this
way the whole field of metabolism is really covered by “regulations.”
Are they real “secondary” ones? Of course the regulatory correspondence
applies to the process of *secretion* in the *first* place, not to the
actual formation of the ferment inside the cell. The correspondence as
to secretion, no doubt, is of the primary type; is there any secondary
regulation with regard to the real *production* of the ferment? I am
sorry that I cannot answer this question affirmatively. Nothing is
*known* at present, even here, that really proves the existence of
adaptation of the secondary type: there *might* be a sort of statical
“harmony” at the base of it all, established before all functioning
*for* functioning.[108]

[108] Compare the excellent review of the subject by Bayliss and
Starling in the *Ergebnisse der Physiologie*, 5, 1906, p. 664. The
reader who misses here an analysis of the brilliant discoveries
of Pawlow and his followers, relating to so-called “psychical and
associative secretion,” will find these facts dealt with in another
section of the book. These facts, indeed, would prove vitalism, it seems
to me.

The only facts of secondary metabolic regulations which are known at
present have been found in combination with phenomena of restitution
after real disturbances of organisation, where, indeed, numbers and
numbers of regulatory changes of metabolism, both in animals and plants,
have also been recorded. But there is not one case of a secondary
regulation really known to affect pure metabolism alone.[109] This is a
new indicium of the primacy of *form* in the organism.

[109] It would be a true secondary metabolic regulation, if after the
extirpation of one gland another different one were to assume its
function. Nothing is known in this respect except a few rather doubtful
observations about the interchange of functions between thymus and
thyroid, except also the fact that the so-called lymph-glands increase
in size after the extirpation of the spleen. Even here, of course, a
sort of “restitution” would be included in adaptation proper.

IMMUNITY THE ONLY TYPE OF A SECONDARY PHYSIOLOGICAL ADAPTATION

There is only one class of physiological processes in which the type
of the real secondary regulation occurs. The discoveries of the last
twenty years have proved beyond all doubt, and future discoveries will
probably prove even more conclusively, that the so-called *immunity*
against diseases is but one case out of numerous biological phenomena
in which there is an adaptive correspondence between abnormal chemical
stimuli and active chemical reactions on the part of the organism and in
its interior, exceeding by far everything that was formerly supposed to
be possible in organic regulation.

The adaptive faculty of the organism against inorganic poisonous
substances[110] is but small comparatively, and is almost always due not
to a real process of active regulation but to the action of substances
pre-existing in the organism--that is, to a sort of adaptiveness but
not adaptation. Metallic poisons, for instance, may be transformed into
harmless compounds by being combined with albumen or sulphuric acid
and thus becoming insoluble, or free acids may be neutralised, and so
on; but all these processes go on to a certain extent only, and, as
was mentioned already, are almost always the result of reactions with
pre-existing materials. Only in a few cases is there any sort of true
adaptation to metallic substances, such as sublimate and, in a very
small degree, arsenic, comparable in some respects with the adaptation
to abnormally high temperatures. The organism which has been accustomed
to receive at first very small amounts, say, of sublimate, and then
receives greater and greater amounts of this substance by degrees, will
at the end of this treatment be able to stand a quantity of the poison
that would have been instantly fatal if administered at the first
dose.[111] But the explanation of this adaptation is not known in any
case; there seems to be some similarity between it and the so-called
histogenetic immunity against organic poisons.

[110] A good review is given by E. Fromm, *Die chemischen Schutzmittel
des Tierkörpers bei Vergiftungen*, Strassburg, 1903.

[111] Davenport, *Arch. Entw. Mech.* 2, 1895-1896, and Hausmann,
*Pflüger’s Arch.* 113, 1906.

It is in the fight against animal and vegetable poisons, such as those
produced by bacteria, by some plants and by poisonous snakes, that the
true adaptation of the organism reaches its most astonishing degree.
The production of so-called “anti-bodies” in the body fluids is not the
only means applied against noxious chemical substances of this kind: the
existence of so-called histogenetic immunity is beyond all doubt, and
Metschnikoff[112] certainly was also right in stating that the cells
of the organism themselves repel the attack of living bacteria. Cells
of the connective tissue and the white blood cells, being attracted by
them as well as by many other foreign bodies, take them in and kill
them. This process, called “phagocytosis” is of special frequency among
lower animals, but it also contributes to what is called inflammation
in higher ones.[113] And there are still other kinds of defence against
parasites, as for instance the horny or calcareous membranes, employed
to isolate trichinae and some kinds of bacteria. But all this is of
almost secondary importance as compared with the adaptive faculties of
the warm-blooded vertebrates, which produce anti-poisonous substances in
their lymph and blood.

[112] *Leçons sur la pathologie comparée de l’inflammation*, Paris, 1902.

[113] The other steps or phases in the process of inflammation have also
been regarded as adaptive: the increased quantity of body fluid for
instance is said to serve to dilute poisonous substances.

It is impossible to say here[114] more than a few words about the
phenomena and the theory of immunity proper, which have attained the
dimensions of a separate science. Let me only mark those general points
which are of the greatest theoretical interest. Discoveries of the most
recent years have shown not only that against the “toxins” of bacteria,
snakes, and some plants, the organism is able actively to produce
so-called “anti-toxins”--that is, soluble substances which react with
the toxins and destroy their poisonous character--whenever required,
but that against any foreign body of the albumen group a specific
reaction may occur, resulting in the coagulation of that body. But the
destruction of the noxious substance or foreign albumen actually present
is not all that is accomplished by the organism. “Acquired immunity”
proper, that is, security against the noxious material for a more or
less extensive period of the *future*, depends on something more. Not
only is there produced as much of the so-called “anti-body” as is
necessary to combine with the noxious, or at least foreign substances
which are present, but *more* is produced than is necessary in the
actual case. On this over-production depends all active immunity,
whether natural or, as in some kinds of vaccination, artificial; and
so-called “passive” immunity, obtained by the transfusion of the serum
of an actively immune organism into another also depends upon this
feature.[115]

[114] See Jacoby, *Immunität und Disposition*, Wiesbaden, 1906.

[115] *Collected Studies on Immunity by Ehrlich and his Collaborators*,
translated by Ch. Bolduan, New York and London, 1906.

This phenomenon in particular--the production of *more* of the
antitoxin or the “precipitin” than is actually necessary--seems to
render almost impossible any merely chemical theory of these facts. The
reaction between toxin and antitoxin, albumen and precipitin is indeed
chemical; it may in fact be carried out in a test-tube; but whether the
production of the anti-body itself is also chemical or not could hardly
be ascertained without a careful and unbiassed analysis. There can be
no doubt that the well-known theory of Ehrlich,[116] the so-called
theory of side-chains (“Seitenkettentheorie”) has given a great impulse
to the progress of science; but even this theory, irrespective of its
admissibility in general, is not a real chemical one: the concept of a
regeneration of its so-called haptophore groups is a strictly biological
concept.[117]

[116] So-called genuine or innate immunity, in contrast to the immunity
which is acquired, is of course a case of adaptedness only and not of
adaptation. There also exists a high degree of specific adaptedness in
some animals with regard to their faculty of coagulating blood. (See Leo
Loeb, *Biol. Bull.* 9, 1905.)

[117] We cannot do more than barely mention here the problem of the
localisation of anti-body production. In general it seems to be true
that anti-bodies are produced by those cells which require to be
protected against toxins; that would agree with the general rule, that
all compensation of the change of any functional state proceeds from the
part changed in its function.

And, indeed, here if anywhere we have the biological phenomenon of
adaptation in its clearest form. There are very abnormal changes of the
functional state of the organism, and the organism is able to compensate
these changes in their minutest detail in almost any case. The problem
of the specification of the reactions leading to immunity seems to me,
as far as I can judge as an outsider, to stand at present in the very
forefront of the science. There cannot be the slightest doubt that
especially against all sorts of foreign albumens the reaction is as
strictly specific as possible; but there are some typical cases of
specificity in the production of antitoxins also. It is, of course,
the *fact* of specific correspondence between stimulus and reaction,
that gives to immunity its central position among all adaptations,
no matter whether the old hypothesis of the production of specific
anti-bodies proves tenable, or whether, as has been urged more recently
by some authors, the anti-body is always the same but reacts differently
according to the medium. In the latter case it would be the medium that
is regulated in some way by the organism in order to attain a specific
adaptedness.

NO GENERAL POSITIVE RESULT FROM THIS CHAPTER

But now let us look back to the sum of all the physiological reactions
studied, and let us see if we have gained a new proof of the autonomy of
life from our long chapter.

We freely admit we have not gained any really new *proof*, but we may
claim, I think, to have gained many indicia for the statement that
the organism is not of the type of a machine, in which every single
regulation is to be regarded as properly prepared and outlined.

It is precisely in the field of immunity that such a machine-like
preparation of the adaptive effects seems almost impossible to be
imagined. How indeed could there be a machine, the chemical constituents
of which were such as to correspond adaptively to almost every
requirement?--to say nothing of the fact that the production of *more*
of the protecting substance than is actually necessary could hardly be
said to be “chemical.”

In fact, we are well entitled to say that we have reached here the very
heart of life and of biology. If nevertheless we do not call the sum of
our facts a real proof of vitalism, it is only because we feel unable
to formulate the analysis of what happens in such a manner as to make
a machine as the basis of all reactions absolutely unimaginable and
unthinkable. There *might* be a true machine in the organism producing
immunity with all its adaptations. We cannot disprove such a doctrine by
demonstrating that it would lead to a real *absurdity*, as we did in our
analysis of differentiation of form; there is only a very high degree of
improbability in our present case. But an indirect *proof* must reduce
to *absurdity* all the possibilities except one, in order to be a proof.

Mechanistic explanations in all branches of functional physiology
proper, so much in vogue twenty years ago, can indeed be said to
have failed all along the line: the only advantage they have brought
to science is the clearer statement of problems to which we are now
accustomed. But we are not fully entitled to say[118] that there never
will be any mechanistic explanation of physiological functions in the
future. It may seem as improbable as anything can be; but we wish to
know not what is improbable but what is not possible.

[118] Here again I should like to except from this statement the
discoveries of Pawlow. See page 204, note 1.

Now of course you might answer me that after we have indeed
shown that the production of form, as occurring on the basis of
harmonious-equipotential systems, is a fact that proves vitalism,
the acts taking place on the basis of that form after its production
would have been proved to be vitalistic also, or at least to be in
some connection with vitalistic phenomena. Certainly they would, and
I myself personally should not hesitate to say so. But that is not
the question. We have to ask: Is any new proof, *independent of every
other*, to be obtained from the facts of physiological adaptation in
themselves? And there is really none. Mere regulatory correspondence
between stimuli and reactions, even if it be of the adaptive type and
occur in almost indefinite forms, never really disproves a machine as
its basis so long as the stimuli and reactions are *simple* and uniform.
Next summer, however, we shall see that vitalism may be proved by such a
correspondence if the two corresponding factors are not simple and not
uniform.

We most clearly see at this point what it really was in our analysis of
differentiation that allowed us to extract a real proof of vitalism from
it. Not the mere fact of regulability, but certain specific relations
of space, of locality, lay at the very foundation of our proof. These
relations, indeed, and only these relations, made it possible to
reduce *ad absurdum* any possible existence of a machine as the actual
basis of what we had studied. In our next chapter again it will be
space-relations, though analysed in a different manner, that will enable
us to add a second real proof of vitalism to our first one.

With this chapter we conclude the study of organic regulation in all its
forms, as far as morphogenesis and metabolism are in question.

But our analysis of these regulations would be incomplete and indeed
would be open to objections, if we did not devote at least a few words
to two merely negative topics, which will be taken more fully into
consideration later on.

A FEW REMARKS ON THE LIMITS OF REGULABILITY

There has never been found any sort of “experience” in regulations
about morphogenesis or in adaptations of the proper physiological
type. Nothing goes on “better” the second time than it did the first
time;[119] everything is either complete, whenever it occurs, or it does
not occur at all.

[119] The few cases of an “improvement” of morphogenetic acts in
hydroids described by myself are too isolated at present to be more
than mere problems (*Arch. Entw. Mech.* 5, 1897). The same is true, it
seems to me, with regard to certain recent discoveries made by R. Pearl
on *Ceratophyllum* (*Carnegie Inst. Wash. Publ.* No. 58, 1907); and by
Zeleny on a medusa (*Journ. exp. Zool.* 5, 1907). Pawlow’s discovery,
that the enzymotic composition of the pancreatic fluid in dogs becomes
more and more adapted to a specific composition of the food (either meat
or bread and milk) the longer such a specific composition is offered
to the individual animal, may probably be understood as a case of mere
functional adaptation of the cells of the digestive glands, if it stands
criticism at all (see Bayliss and Starling, *Ergeb. Physiol.* 5, 1906,
p. 682).

That is the first of our important negative statements about
regulations; the second relates to the phrase just used, “or it does
not occur at all.” There are indeed limits of regulability; adaptations
are not possible to every sort of change of the physiological state:
sickness and death could not exist if they were; nor is restitution
possible in all cases where it might be useful. It is a well-known fact,
that man is only able to heal wounds but is altogether destitute of the
faculty of regeneration proper. But even lower animals may be without
this faculty, as are the ctenophores and the nematodes for instance, and
there is no sort of correspondence between the faculty of restitution
and the place in the animal kingdom. It is not altogether impossible
that there may be found, some day, certain conditions under which every
organism is capable of restoring any missing part; but at present we
know absolutely nothing about such conditions.[120]

[120] Experiments carried out in the “Biologische Versuchsanstalt” at
Vienna indeed have shown that many animal types are capable of at least
a certain degree of restitution, although they had previously been
denied this faculty by zoologists.

But no amount of negative instances can disprove an existing
positive--which is what we have been studying. Our analysis based upon
the existence of regulations is as little disparaged by cases where no
regulability exists as optical studies are by the fact that they cannot
be undertaken in absolute darkness.

*D.* INHERITANCE: SECOND PROOF OF THE AUTONOMY OF LIFE

All organisms are endowed with the faculty of re-creating their own
initial form of existence.

In words similar to these Alexander Goette, it seems to me, has given
the shortest and the best expression of the fact of inheritance. Indeed,
if the initial form in all its essentials is re-created, it follows from
the principle of univocality, that, *ceteris paribus*, it will behave
again as it did when last it existed.

By the fact of inheritance life becomes a rhythmic phenomenon, that is
to say, a phenomenon, or better, a chain of phenomena, whose single
links reappear at constant intervals, if the outer conditions are not
changed.

THE MATERIAL CONTINUITY IN INHERITANCE

It was first stated by Gustav Jaeger and afterwards worked out into
a regular theory by Weismann, that there is a continuity of material
underlying inheritance. Taken in its literal meaning this statement is
obviously self-evident, though none the less important on that account.
For as all life is manifested on bodies, that is on matter, and as the
development of all offspring starts from parts of the parent bodies,
that is from the matter or material of the parents, it follows that in
some sense there is a sort of continuity of material as long as there is
life--at least in the forms we know of. The theory of the continuity of
“germ-plasm” therefore would be true, even if germ-cells were produced
by any and every part of the organism. That, as we know, is not actually
the case: germ-cells, at least in the higher animals and in plants, are
produced at certain specific localities of the organism only, and it is
with regard to this fact that the so-called theory of the “continuity of
germ-plasm” acquires its narrower and proper sense. There are distinct
and specific lines of cell-lineage in ontogenesis, so the theory states,
along which the continuity of germ-protoplasm is kept up, which, in
other words, lead from one egg to the other, whilst almost all other
lines of cell-lineage end in “somatic” cells, which are doomed to
death. What has been stated here is a fact in many cases of descriptive
embryology, though it can hardly be said to be more than that. We know
already, from our analytical and experimental study of morphogenesis,
that Weismann himself had to add a number of subsidiary hypotheses to
his original theory to account for the mere facts of regeneration proper
and the so-called vegetative reproduction in plants and in some animals,
and we have learned that newly discovered facts necessitate still more
appendixes to the original theory. In spite of that, I regard it as
very important that the fact of the continuity of some material as one
of the foundations of inheritance has clearly been stated, even if the
specialised form of the theory, as advocated by Weismann in the doctrine
of the “germ-lineages” (“Keimbahnen”) should prove unable to stand
against the facts.

The important problem now presents itself: What is the material, the
matter, which is handed down from generation to generation as the
basis of inheritance? Weismann, as we know, regarded it as a very
complicated structure, part of which by its disintegration became the
foundation of individual embryology. We have disproved, on the authority
of many facts, the latter part of this assumption; but of course the
first part of it may turn out to be true in spite of this. We have no
means at present to enable us to say *a priori* anything positive or
negative about the important question of the nature of that matter, the
continuity of which in inheritance is in some sense a self-evident fact,
and we therefore shall postpone the answer until a later point of our
analytical discussion.

ON CERTAIN THEORIES WHICH SEEK TO COMPARE INHERITANCE TO MEMORY

It will be advisable first to study some other theoretical views which
have been put forward with regard to inheritance. The physiologist
Hering, as early as 1876, compared all heredity to the well-known fact
of memory, assuming, so to say, a sort of remembrance of all that
has happened to the species in the continuity of its generations;
and several German authors, especially Semon, have lately made this
hypothesis the basis of more detailed speculation.

It is not clear, either from Hering’s paper[121] or from Semon’s
book,[122] what is really to be understood here by the word “memory,”
and, of course, there might be understood by it very different things,
according to the author’s psychological point of view. If he is a
“parallelist” with regard to so-called psychical phenomena, he would use
the word memory only as a sort of collective term to signify a resultant
effect of many single mechanical events, as far as the material world of
his parallel system comes into account, with which of course the problem
of inheritance alone deals; but if he maintains the theory of so-called
psycho-physical interaction, the psychical would be to him a primary
factor in nature, and so also would memory. As we have said, it is by no
means clear in what sense the word “memory” is used by our authors, and
therefore the *most* important point about the matter in question must
remain *in dubio*.

[121] *Ueber das Gedächtnis als eine allgemeine Function der organischen
Materie*, Wien, 1870. New edition in *Klassiker d. exakt. Wiss.*,
Leipzig, Engelmann.

[122] *Die Mneme*, Leipzig, 1904.

But another topic is even more clear in the theory of inheritance, as
stated in Hering’s and Semon’s writings. The hypothetical fact that
so-called “acquired characters” are inherited is undoubtedly the chief
assumption of that theory. Indeed, it would be difficult to understand
the advantage of the ambiguous word memory, had it not to call attention
to the hypothetic fact that the organism possesses the faculty of
“remembering” what once has happened to it or what it once has “done,”
so to speak, and profiting by this remembering in the next generation.
The zoologist Pauly indeed has stated this view of the matter in very
distinct and clear terms.

As we soon shall have another occasion to deal with the much-discussed
problem of the “inheritance of acquired characters,” we at present
need only say a few words about the “memory-theory” as a supposed
“explanation” of heredity. Undoubtedly this theory postulates, either
avowedly or by half-unconscious implication, that all the single
processes in individual morphogenesis are the outcome either of
adaptations of the morphological type, which happened to be necessary
in some former generation, or of so-called contingent “variations,” of
some sort or other, which also happened once in the ancestral line.
Such a postulate, of course, is identical with what is generally called
the theory of descent in any of its different forms. This theory is
to occupy us in the next lectures; at present we only analyse the
“memory-theory” as a theory of heredity in itself. In any case, to
regard memory as the leading point in inheritance, at least if it is to
signify what is called memory in any system of psychology, would be to
postulate that either adaptation or contingent “variation” has been the
origin of every morphogenetic process. Indeed, the American physiologist
Jennings did not hesitate to defend such a view most strongly, and many
others seem to be inclined to do the same.

But such an assumption most certainly cannot be true.

It cannot be true, because there are many phenomena in morphogenesis,
notably all the phenomena akin to restitution of form, which occur
in absolute perfection even the very first time they happen. These
processes, for the simple reason of their *primary perfection*, cannot
be due either to “learning” from a single adaptation, or to accidental
variation. We shall afterwards employ a similar kind of argument to
refute certain theories of evolution. It therefore may be of a certain
logical interest to notice that at present, combating the memory-theory
of inheritance, and hereafter, combating certain theories of descent,
we select not “adaptation” or “variation” as the central points to be
refuted, but the assumed *contingency* of both of them.

The word “memory,” therefore, may be applied to the phenomena of
inheritance only in a very figurative meaning, if at all. We do not
wholly deny the possibility of an inheritance of acquired characters, as
will be seen later on, and to such a fact there might perhaps be applied
such a term as “memory” in its real sense, but we simply *know* that
there *is* something in inheritance which has no similarity whatever
to what is called “memory” in any species of psychology. A primary
perfection of processes occurring quite abnormally proves that there is
a “knowing” of something--if we may say so--but does not prove at all
that there is a “remembering.”

THE COMPLEX-EQUIPOTENTIAL SYSTEM AND ITS RÔLE IN INHERITANCE[123]

[123] Driesch, *Organ. Regul.* 1901.

But we thus far have reached only negative results. Is the question
necessarily to remain at this point, which could hardly be said to be
very satisfying; or could we perhaps get better, that is, positive
results about inheritance by a change of our analytic methods? Let us
try to analyse the facts that occur in inheritance instead of beginning
with hypotheses which claim to be complete explanations. Perhaps we
shall gain, if but small, yet certainly fixed results by an analysis
which goes from the facts to the theory and not from the theory to the
facts.

Let the discussions that are to follow be placed upon a basis as broad
as possible.

Our studies of morphogenetic restitution have shown us that besides the
harmonious-equipotential systems another and widely different type of
morphogenetic “systems” (*i.e.* unities consisting of elements equal in
morphogenetic faculty) may also be the basis of restitution processes.
Whilst in the harmonious system the morphogenetic acts performed by
every single element in any actual case are single acts, the totality
of all the single acts together forming the harmonious whole, in the
other type of systems now to be examined, complex acts, that is, acts
which consist of a manifoldness in space and in time, can be performed
by each single element, and actually are performed by one or the other
of them. We therefore have given the title of “complex-equipotential
systems” to the systems in question, as all our denominations are based
on the concept of the prospective morphogenetic potency, that is of the
possible fate of the elements.

The cambium of the Phanerogams may be regarded as the very type of a
complex-equipotential system, promoting restitution of form. It runs
through the whole stem of our trees, in the form of a hollow tube,
placed between the inner and the outer cell-layers of the stem, and
either branch or root may originate from any single one of its cells,
just as circumstances require. We might call the cambium a system of the
“complex” type of course, even if every one of its constituents were
able to form only a root or only a branch by way of restitution. But in
fact one and the same element can form both of these complex-structures;
it depends only on its relative position in the actual part of the stem
isolated for the purposes of experiment, what will be accomplished in
every case. Here we have a state of affairs, which we shall encounter
again when studying regeneration in animals: every element of the system
may be said to contain potencies for the “ideal whole,” though this
ideal whole will never be realised in its proper wholeness.[124]

[124] The “ideal whole” is also proved to exist, if any *given*
“Anlage,” say of a branch, is forced to give origin to a root, as has
really been observed in certain plants. This case, like many other
less extreme cases of what might be called “compensatory heterotypy,”
are best to be understood by the aid of the concept of “prospective
potency.” It is very misleading to speak of a metamorphosis here. I
fully agree with Krašan about this question. See also page 112, note 1,
and my *Organ. Regul.* pp. 77, 78.

But there is no need to recur to the “ideal whole” in many other cases
of adventitious restitution in plants. On isolated leaves of the
well-known begonia, a whole plant, containing all the essential parts,
may arise from any single cell[125] of the epidermis, at least along the
veins, and in some liverworts it has been shown by Vöchting, that almost
every cell of the whole is able to reproduce the plant, as is also the
case in many algae.

[125] Winkler has discovered the important fact, that the adventitious
buds formed upon leaves may originate either from one single cell of
the epidermis or from several cells together; a result that is very
important with respect to the problem of the distribution of “potencies.”

In the animal kingdom it is chiefly and almost solely the phenomena
of regeneration proper which offer typical instances of our systems,
since adventitious restitution, though occurring for instance in the
restitution of the lens of vertebrates from the iris, and though
connected also with the events in regeneration proper,[126] is of but
secondary importance in animal restitution, at least, if compared with
restitution in plants. If we study the regeneration of a leg in the
common newt, we find that it may take place from every section, the
point of amputation being quite at our choice. Without regarding here
the exact order of the regeneration phenomena, which is almost unknown
at present, we in any case can say without any doubt that the line
of consecutive possible cross-sections forms a complex-morphogenetic
system, as every one of them is able to give rise to a complex organ,
viz. the foot and part of the leg. It is an open question whether this
complex system is to be called “equipotential” or not. It indeed seems
to be inequipotential at the first glance, for each single section has
to form a different organogenetic totality, namely, always that specific
totality which had been cut off; but if we assume hypothetically that
the real “Anlage” which is produced immediately by the cells of the
wounded surface is the very same for all of them, and that it is the
actual state of organisation which determines to what result this
Anlage is to lead,[127] we may say that the series of consecutive
cross-sections of a newt’s leg does form a morphogenetic system of the
complex-equipotential type, promoting secondary regulations of form.

[126] The “regeneration” of the brain of annelids for instance is far
better regarded as an adventitious formation than as regeneration
proper: nothing indeed goes on here at the locality of the wound; a new
brain is formed out of the ectoderm at a certain distance from it.

[127] A full “analytical theory of regeneration” has been developed
elsewhere (*Organ. Regul.* p. 44, etc.). I can only mention here that
many different problems have to be studied by such a theory. The
formation of the “Anlage” out of the body and the differentiation of
it into the completely formed results of regeneration are two of them.
The former embraces the question about the potencies not only of the
regenerating body but of the elements of the Anlage also; the latter
has to deal with the specific order of the single acts of regenerative
processes.

Now all these difficulties vanish, if we consider the regeneration of
animals, such for instance as many worms of the annelid class or our
familiar ascidian *Clavellina*, in which regeneration in both directions
is possible. The wound at the posterior end of the one half which
results from the operation forms a posterior body half, the wound at
the anterior end of the other half forms an anterior one. Again, it is
the ideal whole which we meet here: each section of the body indeed may
be said to contain the potencies for the production of the totality,
though actually this totality is always realised by the addition of two
partial organisations. The title of complex-equipotential systems thus
seems to be fully justified as applied to the systems which are the
basis of regeneration: each section of the regenerating body may in fact
produce the same complex whole, or may, if we prefer to say so, at least
prepare the ground for that complex Anlage, out of which the complex
totality is actually to arise, in the same manner.

It often occurs in science, that in rather strange and abnormal
conditions something becomes apparent which might have been found
everywhere, which is lying before our eyes quite obviously. Are
we not in just such a condition at present? In order to study the
complex-equipotential systems, we turn to the phenomena of regeneration
and of restitution in general; we occasionally even introduce hypotheses
to render our materials more convenient for our purposes; and all the
time there is one sort of complex-equipotential system in the body of
every living being, which only needs to be mentioned in order to be
understood as such, and which indeed requires no kind of preliminary
discussion. The system of the propagation cells, in other words the
sexual organ, is the clearest type of a complex-equipotential system
which exists. Take the ovary of our sea-urchin for instance, and there
you have a morphogenetic system every element of which is equally
capable of performing the same complex morphogenetic course--the
production of the whole individual.

Further on we shall deal exclusively with this variety of our systems,
and in doing so we shall be brought back to our problem of heredity. But
it had its uses to place our concept of the complex-equipotential system
upon such a broad basis: we at once gave a large range of validity to
all that is to follow--which, indeed, does not apply to inheritance
alone, though its significance in a theory of heredity may be called its
most important consequence.

THE SECOND PROOF OF LIFE-AUTONOMY. ENTELECHY AT THE BOTTOM OF INHERITANCE

After we had established the concept of the harmonious-equipotential
system in a former chapter, we went on to study the phenomena of the
differentiation of it, and in particular the problem of the localisation
of all differentiations. Our new concept of the complex-equipotential
system is to lead us to an analysis of a different kind: we shall pay
special attention to the origin, to the *genesis* of our complex systems
that show equipotentiality.

If we review the process of ontogenesis, we are able to trace back every
complex system to a very small group of cells, and this small group of
cells again to one single cell. So in plants the cambium may be shown
to have originated in a sort of tissue-rudiment, established at a very
early period, and the ovary may be demonstrated to be the outcome of a
group of but a few cells, constituting the first visible “Anlage” of the
reproductive organs. At the end then, or from another point of view at
the beginning, a single cellular element represents the very primordial
egg-cell.

The whole cambium, there can be no doubt, must be regarded as the result
of a consecutive number of cell-divisions of the one cell from which it
originates. So must it be with the ovary. The primordial egg-cell has
undergone a long line of consecutive divisions; the single eggs are the
last result of them.

We now proceed to some considerations which have a certain
logical similarity to those which inaugurated our analysis of the
differentiation of the harmonious-equipotential systems, though the
facts in question are very different.

Viewed by itself without any kind of prepossessions, as it might
be by any one who faces a new problem with the single postulate of
introducing new natural entities--to use the scholastic phrase--as
little as possible, the development of the single egg might be regarded
as proceeding on the foundation of a very complicated sort of machine,
exhibiting a different kind of construction in the three chief
dimensions of space, as does also the organism which is to be its result.

But could such a theory--irrespective of all the experimental facts
which contradict it--could such a theory stand before the *one* fact,
that there occurs a *genesis* of that complex-equipotential system,
of which our one single egg forms a part? Can you imagine a very
complicated machine, differing in the three dimensions of space, to
be divided hundreds and hundreds of times and in spite of that to
remain always the same whole? You may reply that during the period
of cell-divisions there is still no machine, that the machine is
established only after all the divisions are complete. Good; but what
then constructs this machine in the definitive cells of our systems, say
in the eggs? Another sort of machine perhaps? That could hardly be said
to be of much use. Or that entelechy of which we have spoken? Then you
would recur to our first proof of vitalism and would burden entelechy
with a specific performance, that is with the construction of the
hypothetic machine which you are postulating in every single egg. But of
course you would break the bounds of physics and chemistry even then.

It seems to me that it is more simple, and so to say more natural, not
to recur to our first proof of life-autonomy in order to keep to the
“machine theory” in this new branch of inquiry, but to consider facts as
they offer themselves to analysis.

But then indeed we are entitled to draw an independent second proof of
the autonomy of life from our analysis of the genesis of systems of the
complex-equipotential type. We say it is a mere absurdity to assume that
a complicated machine, typically different in the three dimensions of
space, could be divided many many times, and in spite of that always
be the whole: therefore there cannot exist any sort of machine as the
starting-point and basis of development.

Let us again apply the name entelechy to that which lies at the very
beginning of all individual morphogenesis.

Entelechy thus proves to be also that which may be said to lie at
the very root of inheritance,[128] or at least of the outcome of
inheritance; the individual formation of the next generation is shown
not to be performed by a machine but by a natural agent *per se*.

[128] And, of course, at the root of every new starting of certain
parts of morphogenesis also, as in regeneration and in adventitious
budding; these processes, as we know, being also founded upon
“complex-equipotential systems,” which have had their “genesis.”

THE SIGNIFICANCE OF THE MATERIAL CONTINUITY IN INHERITANCE

But what about the material continuity appearing in inheritance, which
we have said to be almost self-evident, as life is only known to exist
on material bodies? Is there not, in fact, a serious contradiction
in admitting at the same time entelechy on the one side and a sort
of material condition on the other as the basis of all that leads to
and from inheritance? Next summer the relation between matter and our
autonomous agent of life will be studied more fully; at present it must
be enough to state in a more simple and realistic way, what we hold
this relation to be. There is no contradiction at all in stating that
material continuity is the basis of inheritance on the one side, and
entelechy on the other. It would be very inconvenient for us if there
were any: for the material continuity is a mere fact and our entelechy
we hope we have proved to exist also; if now there were any sort of
contradiction in assuming the existence of both of them, of course it
would be fatal to our proof.

Let us try to comprehend what is meant by the statement that entelechy
and something material are at work in inheritance at the same time.
Entelechy has ruled the individual morphogenesis of the generation which
is regarded as being the starting-point for inheritance, and will rule
also the morphogenesis of the generation which is to follow; entelechy
determines the egg to be what it is, and the morphogenesis starting from
this egg to be what it is also. Entelechy, at present, is not much more
for us than a mere word, to signify the autonomous, the irreducible of
all that happens in morphogenesis with respect to *order*, in the one
generation and in the next. But may not the material continuity which
exists in inheritance account perhaps for the material elements *which
are to be ordered*? In such a way, indeed, I hope we shall be able to
reconcile entelechy and the material basis of heredity. May it not be
that there exist some “means” for morphogenesis, which are handed down
from generation to generation, always controlled by entelechy, and which
constitute the real significance of the continuity of matter during
inheritance?

THE EXPERIMENTAL FACTS ABOUT INHERITANCE

Discoveries of the last few years do seem to show that such means
of a material character, though not the foundation of that order of
processes which is inherited, are nevertheless among the most necessary
conditions for the accomplishment of inheritance in general. It is
scarcely necessary to remind you that for very many years all concrete
research on heredity proper--that is, the actual comparison of the
various specific characters in the generations of the grandfather, the
father, and the child--was due to Galton. You may also be aware that in
spite of Galton’s inestimable services it was not till 1900 that one of
the active principles concerned in inheritance was found independently
by de Vries, Correns, and Tschermak, and that this principle happened
to be one that *had* been discovered already, stated with the utmost
clearness and precision by the Augustinian monk, Gregor Mendel,[129] as
early as 1865, though it had been completely forgotten ever since.

[129] New edition in the “Klassiker d. exakt. Wiss.” Leipzig, Engelmann;
see also Bateson, *Mendel’s Principles of Heredity*, Cambridge, 1902.

The so-called “rule of Mendel” is based upon experiments with hybrids,
that is, with the offspring of parents belonging to different species,
or, at least, varieties, but it relates not to the characters of the
generation resulting immediately from hybridisation, the “first”
generation of hybrids, as we shall call it, but to the characters of
that generation which is the result of crossing the hybrids with each
other, provided that this leads to any offspring at all. There are many
cases indeed, both amongst animals and plants, where the offspring of
the hybrids, or in other terms the “second” generation, is found to
consist of individuals of three different types--the mixed[130] type
of the hybrids themselves, and the two pure types of the grandparents.
Whenever the individuals of the “second” generation are separated into
these three different types, hybrids are said to “split.” It is the
fact of this splitting on the one hand, and on the other hand a certain
statement about the numbers of individuals in the three different types
of the “second” generation, that gives its real importance to Mendel’s
rule.

[130] For the sake of simplicity I shall not deal here with those
cases of hybridisation in which one quality is “recessive,” the other
“dominant,” but only allude to the cases, less numerous though they be,
where a real mixture of maternal and paternal qualities occurs.

Before discussing what may follow from Mendel’s discovery for the
theory of heredity, we must lay stress on the fact that there are many
exceptions to his rule. In quite a number of cases the hybrids are of
one or more types, which remain constant: there is no splitting at all
in the second generation. But that does not affect the rule of Mendel in
those cases where it is true. Where there is a “splitting” in the second
generation, there also are the numerical proportions stated by Mendel;
there never are other relations among the numbers of individuals of the
mixed and of the two pure types than those given by his rule. I regard
it as very important that this real meaning of Mendel’s principle should
be most clearly understood.

From the fact of the splitting of hybrids in the second generation most
important consequences may be drawn for the theory of inheritance; the
split individuals, if crossed with each other, always give an offspring
which remains pure; there is no further splitting and no other change
whatever. The germ-cells produced by the split individuals of the second
generation may therefore be said to be “pure,” as pure as were those of
the grandparents. But that is as much as to say that the pureness of
the germ-cells has been preserved in spite of their passing through the
“impure” generation of the hybrids, and from this fact it follows again
that the union of characters in the hybrids must have been such as to
permit pure separation: in fact, the germ-cells produced by Mendelian
hybrids may hypothetically be regarded as being pure themselves.[131]

[131] This hypothesis was first suggested by Sutton and is at present
held by orthodox Mendelians; but probably things are a little more
complicated in reality, as seems to be shown by some facts in the
behaviour of so-called “extracted recessives.” In Morgan’s *Experimental
Zoology*, New York, 1907, a full account of the whole matter is given.

We have not yet considered one feature of all experiments in
hybridisation, which indeed seems to be the most important of all for
the theory of inheritance, if taken together with the fact of the
pureness of the germs. The rule of Mendel always relates to one single
character of the species or varieties concerned in hybridisation, and
if it deals with more than one character, it regards every one of them
separately; indeed, the rule holds for every one of them irrespective
of the others. We cannot study here how this most important fact of
the independence of the single characters of a species with regard to
inheritance leads to the production of new races, by an abnormal mixture
of those characters. We only take advantage of the fact theoretically,
and in doing so, I believe, we can hardly escape the conclusion that
the independence of the single characters in inheritance, taken
together with the pureness of the germ-cells in the most simple form
of hybrids, proves that there occurs in inheritance a sort of handing
over of single and separate morphogenetic agents which relate to the
single morphogenetic characters of the adult. We may use Bateson’s
word “allelomorphs” for these agents, or units, as they may be called,
thereby giving expression to the fact that the single and separate
units, which are handed over in inheritance, correspond to each other in
nearly related species without being the same.

And so we have at least an inkling of what the material continuity of
inheritance is to mean, though, of course, our “single and separate
morphogenetic agents,” or “units” or “allelomorphs” are in themselves
not much more than unknown somethings described by a word; but even then
they are “somethings.”

Besides the researches relating to the rule of Mendel and its
exceptions, founded, that is, upon a study of the “second” generation of
hybrids, there is another important line of research lately inaugurated
by Herbst, which investigates the first generation in hybridisation.
The hybrids themselves are studied with the special purpose of finding
out whether the type of the single hybrid may change according to the
conditions of its development, both outer and inner. The discoveries
thus made may lead some day to a better understanding of the intimate
nature of the “units” concerned in heredity, and perhaps to some
knowledge of the arranging and ruling factor in morphogenesis also.

Starting from the discovery of Vernon, that the hybrids of sea-urchins
are of different types according to the season, Herbst[132] was able
to show that differences among the hybrids with regard to their being
more of the paternal or more of the maternal type, are in part certainly
due to differences in temperature. But there proved to be still another
factor at work, and Herbst has succeeded in discovering this factor by
changing the internal conditions of morphogenesis. Whenever he forced
the eggs of *Sphaerechinus* to enter into the first[133] phase of
artificial parthenogenesis and then fertilised them with the sperm of
*Echinus*, he was able to approximate the offspring almost completely
to the maternal type, whilst under ordinary conditions the hybrids in
question follow the paternal far more than the maternal organisation.

[132] *Arch. Entw. Mech.* 21, 22, and 24, 1906-7; see also Doncaster,
*Phil. Trans. Royal Soc.* London, B. 196, 1903. The influence of
different temperature upon the organisation of the hybrids is not
always quite pure, inasmuch as the paternal and the maternal forms may
themselves be changed by this agent. In spite of that there exists an
influence of the temperature upon the hybrid *as such*, at least with
regard to certain features of its organisation.

[133] Only the nucleus of the egg had entered its first stages of
activity.

What is shown, in the first place, by these discoveries is the
importance of an arranging and ruling factor in spite of all units. The
organism is always one *whole* whether the paternal properties prevail
or the more complicated maternal ones; in other words, all so-called
properties that consist in the *spatial relations of parts* have nothing
to do with “units” or “allelomorphs,” which indeed cannot be more
than necessary means or materials, requiring to be ordered. As to the
character of the morphogenetic single and separate units themselves
Herbst is inclined to regard them as specific chemical substances which
unite correspondingly during nuclear conjugation, forming a sort of
loose chemical compound. It would depend on the constitution of this
compound whether germ-cells of hybrids could become pure or not.

THE RÔLE OF THE NUCLEUS IN INHERITANCE

At the end of our studies on heredity we hardly can avoid saying a
few words about the problem of the localisation of the morphogenetic
units in the germ-cells themselves. Is it in the protoplasm or in the
nucleus that they are placed? You all know that this question was for
a long time regarded as more important than any other, and perhaps
you have already blamed me for not raising it until now. But in my
opinion results gained by the purely analytical method and carefully
established, are always superior to those which are of a merely
descriptive nature and doubtful besides. The famous problem of the part
played by the nucleus in inheritance is both descriptive and doubtful:
it is only, so to say, of factual, not of analytical importance, and
quite insoluble at present.

As for our second proof of vitalism, stating that no kind of machine
inside the germ-cells can possibly be the foundation of their
morphogenesis, it is clear that the protoplasm and the nucleus may both
come into account here on equal terms. If you prefer to say so, it is to
the nucleus and to its division in particular that the second proof of
autonomy relates, while the first, though not over-looking the presence
of nuclei,[134] deals “especially” with the protoplasmic nature of its
“systems.”

[134] The first proof of vitalism, indeed, rests upon the analysis of
the differentiation of an harmonious-equipotential system as a *whole*:
this *whole* cannot be a machine that would relate to differentiation as
a *whole*; the question whether there might be any machines distributed
*in* the whole, in the form of the nuclei is of no importance at all in
this argument. Moreover the pressure experiments (see page 63) prove the
unimportance of such “machines” for the specificity of differentiation,
and the second proof of vitalism shows that the nuclei cannot be
regarded as machines accounting for differentiation in *any* way.

What then can we say, on the basis of actual facts, about the part taken
by the protoplasm and by the nucleus in inheritance, now that we have
learnt from our analytical discussion that both of them cannot be any
kind of morphogenetic machine, but can only be means of morphogenesis?
Let us state our question in the following way: whereabouts in the
germ-cells are those “means” of morphogenesis localised, the existence
of which we infer from the material continuity in the course of
generations in general and from the facts discovered about hybridisation
in particular?

The first of the facts generally said to support the view that the
nucleus of the germ-cells exerts a specified influence upon the
processes of development and inheritance, relates to the proportion
between protoplasm and nuclear material in the egg and in the spermiae.
This proportion is very different in the two sexual products, as we
know, there being an enormous preponderance of the protoplasm in the
egg, of the nucleus in the spermatozoon. This seems to indicate that
the proportion between protoplasm and nucleus is fairly indifferent
for inheritance, as all the facts go to show that inheritance from
the father is as common as inheritance from the mother. It is in the
nucleus, and in the nucleus alone, that any similarity of organisation
exists between the two sexual products, so very different in all other
respects: therefore the nucleus should be the organ of inheritance. The
phenomena of nuclear division, of karyokinesis, which are quite equal in
both sexual cells, are certainly well fitted to support this hypothesis.

There seems indeed to be some truth in this reasoning, but nevertheless
it must remain hypothetical; and it must never be forgotten that
there may be very probably some sort of morphogenetic importance in
protoplasm also. Rauber and afterwards Boveri[135] have tried to prove
experimentally that it is on the nuclear chromatic substance only that
inheritance depends, but the first of these authors failed to get any
results at all, and the latter obtained only ambiguous ones. Godlewski,
on the contrary, has fertilised purely protoplasmic egg-fragments of
the sea-urchin with the sperm of quite another group of Echinoderms,
and obtained in spite of that a few stages of development of the
pure maternal type. This experiment seems to place the morphogenetic
importance of protoplasm beyond all doubt.

[135] Boveri tried to fertilise enucleated fragments of the egg of
*Sphaerechinus* with the sperm of *Echinus*. He failed to get any
results in isolated experiments, but found a few small larvae of the
pure *Echinus* type in large cultures consisting of shaken eggs. But
later experiments on hybridisation in sea-urchins have shown that a full
hybrid of *Echinus* and *Sphaerechinus* may be purely paternal also.

I should prefer not to make any definite statement about our problem at
present. Our actual knowledge of the organisation and metabolism of both
nucleus and protoplasm is so extremely small and may relate to such very
insignificant topics, that any definite decision is impossible. I myself
believe that the nucleus plays an important part in heredity, perhaps
even a greater one than protoplasm, but this is only my belief.[136]

[136] Surely the new results of Herbst, mentioned above, are another
indication of the importance of something in the nucleus. The first
stage in parthenogenesis, which he used in his experiments, is a nuclear
phenomenon.

The discovery of Gruber and others, that Protozoa are only capable of
restitution if they contain at least a fragment of the nucleus, has
also been used occasionally as a proof of the morphogenetic importance
of the nucleus. But might not this absence of restitution where nuclear
material is lacking be understood equally well on the hypothesis of Loeb
and R. S. Lillie that the nucleus is a centre of oxidation in the cell?
Remove the heart from a vertebrate and the animal will not digest any
more; but in spite of that the heart is not the organ of digestion.

And so we lay stress once more upon this point: that the experimental
results of hybridisation and the analytical results obtained by the
discussion of the complex-equipotential systems are of greater value
to the theory of heredity than all speculation about the importance or
unimportance of special constituents of the cell, of whose organisation,
chemistry, and physics, scarcely anything is known at present.[137]

[137] Boveri (*Ergebn. üb. d. Konstitution etc. des Zellkerns*, Jena,
1904; and “Zellen-Studien VI.” *Jen. Zeitschr.* 43, 1907) has made it
highly probable by experiments that the different chromosomes of the
nucleus of the sexual products play a different part in morphogenesis,
though not in the sense of different single representatives of
different single organs. This doctrine, of course, would not alter
the whole problem very much: the chromosomes would only be *means* of
morphogenesis and nothing else, no matter whether they were of equal or
of different formative value. It only is with regard to the problem of
the determination of sex (see page 107, note 3), that the morphogenetic
singularity of *one* certain specific chromosome can be said to be
proved.

VARIATION AND MUTATION

Heredity, it has been said, may be understood as resting upon the fact
that each organism forms its own initial stage again, and that this
initial stage always encounters conditions of the same kind.

If this statement were quite correct, all the individuals of a given
species would be absolutely alike everywhere and for ever. But they
are not alike; and that they are not alike everywhere and for ever is
not merely the only real foundation of the so-called theory of descent
we possess, but also forces us to change a little our definition of
heredity, which now proves to have been only a sort of approximation to
the truth, convenient for analytical discussion.

In the first place, the conditions which surround the initial stages
of morphogenesis are not quite equal in every respect: and indeed
the offspring of a given pair of parents, or better, to exclude all
complications resulting from sexual reproduction, or amphimixis, as
Weismann called it--the offspring of one given parthenogenetic female
are not all equal among themselves. The individuals of each generation
are well known to vary, and it is especially in this country that the
so-called individual or fluctuating variation has been most carefully
studied by statistical methods, Galton and Weldon being the well-known
pioneers in this field.[138] In fact, if we are allowed to assume that
this sort of variation is the outcome of a variation of conditions--in
the most general meaning of the word--we only follow the opinion
which has almost universally been adopted by the biologists[139] that
are working at this branch of the subject. Variation proper is now
generally allowed to be the consequence of variations in nutrition;
the contingencies of the latter result in contingencies of the former,
and the law of contingencies is the same for both, being the most
general law of probability. Of course under such an aspect fluctuating
variation could hardly be called an exception, but rather an addition to
inheritance.

[138] H. M. Vernon, *Variations in Animals and Plants*, London, 1903.

[139] De Vries, *Die Mutationstheorie*, i., 1901; and Klebs, *Jahrb.
wiss. Bot.* 42, 1905.

But there are other restrictions of our definition of heredity. The
initial stage which is formed again by an organism is not always quite
identical in itself with the initial stage of its own parent: Bateson
and de Vries were the first to study in a systematic way these real
exceptions[140] to true inheritance. As you know, de Vries has given
them the name of “mutations.” What is actually known on this subject is
not much at present, but nevertheless is of great theoretical value,
being the only real foundation of all theories of descent, as we shall
see in the next lectures. “Mutations” are known to exist at present only
among some domesticated animals and plants. Nothing of a more general
character can be said about their law or meaning.[141]

[140] They would not be “real exceptions” if Klebs (*Arch. Entw. Mech.*
24, 1907) were right in saying that both variations and mutations owe
their existence to external agents. What is really *proved* by Klebs
is the possibility of changing the *type* of a curve of variation and
of provoking certain discontinuous varieties by external means. See
also Blaringhem (*Comptes rend.* 1905-6, and *Soc. de Biol.* 59, 1905),
and MacDougal (*Rep. Depart. Bot. Res., 5th Year-book Carnegie Inst.*,
Washington, 129).

[141] H. de Vries, *Species and Varieties: their Origin by Mutation*,
London, 1905. A short review of the “mutation-theory” is given by Francé
in *Zeitschrift f. d. Ausbau d. Entwickelungslehre*, i. 1907. It is well
known that Gautier, and, in the first place, Korshinsky, advocated a
similar view previous to the authors named in the text.

CONCLUSIONS FROM THE FIRST MAIN PART OF THESE LECTURES

In finishing our chapter on inheritance, we at the same time have
finished the first main part of our lectures; that part of them which
has been devoted exclusively to the study of the morphogenesis of the
*individual*, including the functioning of the adult individual form.
We now turn to our second part, which is to deal with the problems of
the diversities of individual forms, with morphological systematics. The
end of our chapter on inheritance has already led us to the threshold of
this branch of biological science.

The chief result of the first main part of our lectures has been to
prove that an autonomy of life phenomena exists at least in some
departments of individual morphogenesis, and probably in all of them;
the real starting-point of all morphogenesis cannot be regarded as a
machine, nor can the real process of differentiation, in all cases where
it is based upon systems of the harmonious equipotential type. There
cannot be any sort of machine in the cell from which the individual
originates, because this cell, including both its protoplasm and its
nucleus, has undergone a long series of divisions, all resulting in
equal products, and because a machine cannot be divided and in spite of
that remain what it was. There cannot be, on the other hand, any sort
of machine as the real foundation of the whole of an harmonious system,
including many cells and many nuclei, because the development of this
system goes on normally, even if its parts are rearranged or partly
removed, and because a machine would never remain what it had been in
such cases.

If our analytical discussions have thus led us to establish a typical
kind of vitalism, it follows that we can by no means agree with Wilhelm
Roux in his denomination of the analytical science of the individual
form and form-production as “Entwickelungsmechanik,” “developmental
mechanics,” a title, which, of course, might easily be transformed
into that of “morphogenetic mechanics,” to embrace not only normal
development, but restitution and adaptation too. We feel unable to speak
of “mechanics” where just the contrary of mechanics, in the proper
meaning of the word, has been proved to exist.

Names of course are of comparatively small importance, but they
should never be allowed to be directly misleading, as indeed the term
“Entwickelungsmechanik” has already proved to be. Let us rather say,
therefore, that we have finished with this lecture that part of our
studies in biology which has had to deal with morphogenetic physiology
or physiological morphogenesis.

Once more we repeat, at this resting-point in our discussions, that both
of our proofs of life-autonomy have been based upon a careful analysis
of certain facts about the distribution of morphogenetic potencies in
two classes of morphogenetic systems, and upon nothing else. To recall
only one point, we have not said that regeneration, merely because it
is a kind of restitution of the disturbed whole, compels us to admit
that biological events happen in a specific and elemental manner, but,
indeed, regeneration *does* prove vitalism, because it is founded upon
the existence of certain complex-equipotential systems, the analysis of
the genesis of which leads to the understanding of life-autonomy. This
distinction, in fact, is of the greatest logical importance.

PART II

SYSTEMATICS AND HISTORY

*A.* THE PRINCIPLES OF SYSTEMATICS

RATIONAL SYSTEMATICS

All systematics which deserves the predicate “rational” is founded
upon a concept or upon a proposition, by the aid of which a totality
of specific diversities may be understood. That is to say: every
system claiming to be rational gives us a clue by which we are able to
apprehend either that there cannot exist more than a certain number of
diversities of a certain nature, or that there can be an indefinite
number of them which follow a certain law with regard to the character
of their differences.

Solid geometry, which states that only five regular bodies are possible,
and points out the geometrical nature of these bodies, is a model
of what a rational system should be. The theory of conic sections
is another. Take the general equation of the second degree with two
unknowns, and study all the possible forms it can assume by a variation
of its constants, and you will understand that only four different types
of conic sections are possible--the circle, the ellipse, the hyperbola,
and the parabola.

In physics and chemistry no perfect rational systems have been
established hitherto, but there are many systems approaching the ideal
type in different departments of these sciences. The chemical type of
the monohydric saturated alcohols, for instance, is given by the formula
C_nH_{2n+1}OH, and in this formula we not only have an expression of
the law of composition which all possible alcohols are to follow,--but,
since we know empirically the law of quantitative relation between
*n* and various physical properties, we also possess in our formula a
general statement with respect to the totality of the properties of any
primary alcohol that may be discovered or prepared in the future. But
chemistry has still higher aims with regard to its systematics: all of
you know that the so-called “periodic law of the elements” was the first
step towards a principle that may some day give account of the relation
of all the physical and chemical properties of any so-called element
with its most important constant, the atomic weight, and it seems to be
reserved for the present time to form a real fundamental system of the
“elements” on the basis of the periodic law by the aid of the theory
of electrons. Such a fundamental system of the elements would teach us
that there can only be so many elements and no more, and only of such a
kind. In crystallography a similar end has been reached already by means
of certain hypothetic assumptions, and systematics has here accounted
for the limited number and fixed character of the possible forms of
crystalline symmetry.

It is not difficult to understand the general logical type of all
rational systems, and logic indeed can discover it without appealing
to concrete sciences or to geometry. Rational systematics is always
possible whenever there exists any fundamental concept or proposition
which carries with it a principle of division; or to express it somewhat
differently, which would lead to contradictions, if division were to
be tried in any but one particular manner. The so-called “genus,” as
will easily be perceived, then embraces all its “species” in such a
manner that all peculiarities of the species are represented already in
properties of the genus, only in a more general form, in a form which
is still unspecified. The genus is both richer in content and richer in
extent than are the species, though it must be added that its richness
in content is, as it were, only latent: but it may come into actuality
by itself and without any help from without.

We are dealing here with some of the most remarkable properties of the
so-called synthetic judgments *a priori* in the sense of Kant, and,
indeed, it seems that rational systematics will only be possible where
some concept of the categorical class or some proposition based upon
such concept lies at the root of the matter or at least is connected
with it in some way. In fact, all rational systems with regard to the
relations of symmetry in natural bodies deal ultimately with space; or
better, all systems in such fields are able to become rational only if
they happen to turn into questions of spatial symmetry.

All other genera and species, whether of natural bodies or of facts,
can be related only on the basis of empirical abstraction, *i.e.* can
never attain rationality: here, indeed, the genus is richer in extent
and poorer in content than are the species. The genus is transformed
into the species, not by any inherent development of latent properties,
but by a mere process of addition of characteristic points. It is
impossible to deduce the number or law or specifications of the species
from the genus. Mere “classification,” if we may reserve the honorable
name of systematics for the rational type, is possible here, a mere
statement in the form of a catalogue, useful for orientation but for
nothing more. We may classify all varieties of hats or of tables in the
same way.

BIOLOGICAL SYSTEMATICS

At this point we return from our logical excursion to our proper subject
of biology; for I am sorry to say biological systematics is at present
of our second type of systematics throughout: it is classification pure
and simple. We have a catalogue in our hands, but nothing more.

Such a statement of fact conveys not a particle of censure, casts not
the least reflection on the gifted men who created the classification of
animals or plants. It is absolutely necessary to have such a catalogue,
and indeed the catalogue of the organisms can be said to have been
improved enormously during the advance of empirical and descriptive
biological science. Any classification improves as it becomes more
“natural,” as the different possible schemes of arrangement, the
different reasons of division, agree better and better in their results;
and, in fact, there has been a great advance of organic classification
in this direction. The “natural” system has reached such perfection,
that what is related from one point of view seems nearly related also
from almost all points of view which are applicable, at least from those
which touch the most important characteristics. There has been a real
weighing of all the possible reasons of division, and that has led to a
result which seems to be to some extent final.

But, nevertheless, we do not understand the *raison d’être* of the
system of organisms; we are not at all able to say that there must be
these classes or orders or families and no others, and that they must be
such as they are.

Shall we ever be able to understand that? Or will organic systematics
always remain empirical classification? We cannot answer this question.
If we could, indeed, we should have what we desire! As simple relations
of space are certainly not the central point of any problematic rational
organic systematics even of the future, the question arises, whether
there could be found any principle of another type in the realm of
synthetic *a priori* judgments which could allow an inherent sort of
evolution of latent diversities, as do all judgments about spatial
symmetry. At the end of the second course of these lectures, which is to
be delivered next summer, we shall be able to say a few more words about
this important point.

The concept of what is called “a type,” due almost wholly to Cuvier and
Goethe, is the most important of all that classification has given to
us. Hardly second in importance is the discovery of the “correlation of
parts,” as a sort of connection which has the character of necessity
without being immediately based upon causality. Rádl seems to be
the only modern author who has laid some stress on this topic. The
harmony which we have discovered in development is also part of this
correlation. When, later on, we come to discuss analytically our well
established entelechy as the ultimate basis of individual organisation,
we shall be able to gain more satisfactory ideas with respect to the
meaning of the non-causal but necessary connection, embraced in the
concepts of type and of correlation of parts.

The type is a sort of irreducible arrangement of different parts; the
correlation deals with the degree and the quality of what may be called
the actual make of the parts, in relation to one another: all ruminants,
for instance, are cloven-footed, the so-called dental formulae are
characteristic of whole groups of mammals. Of course all such statements
are empirical and have their limits: but it is important that they are
possible.[142]

[142] Recent years have created the beginnings of a systematics based on
chemical differences of metabolism and its products: such differences in
fact have been found to go hand in hand with diversities of the type in
some cases (v. Bunge, Przibram, etc.).

It has been the chief result of comparative embryology to show that the
type as such is more clearly expressed in developmental stages than
it is in the adults, and that therefore the embryological stages of
different groups may be very much more similar to each other than are
the adults: that is the truth contained in the so-called “biogenetisches
Grundgesetz.” But the specific differences of the species are not
wanting in any case of ontogeny, in spite of such similarities in
different groups during development.

We have applied the name “systematics” or, if rationality is excluded,
“classification” to all that part of a science which deals with
diversities instead of generalities: in such a wide meaning systematics,
of course, is not to be confused with that which is commonly called so
in biology, and which describes only the exterior differences of form.
Our systematics is one of the two chief parts of biology; what are
called comparative anatomy and comparative embryology are its methods.
For it must be well understood that these branches of research are only
methods and are not sciences by themselves.

*B.* THE THEORY OF DESCENT

1. GENERALITIES

It is most generally conceded at the present time that the actually
existing state of all organisms whatsoever is the result of their
history. What does that mean? What are the foundations upon which the
assumption rests? What is the relation of systematics to history? In
raising such questions and considerations we are treading the ground
sacred to the theory of descent.

I well know that you prefer the name “theory of evolution” for what
I am speaking of: but it may be misleading in various respects. We
already know that quite a determinate meaning has been given to the word
“evolutio” as applied to individual morphogenesis, “evolutio” being
here opposed to “epigenesis.” Now there would be nothing against the
use of the word evolution in a wider sense--indeed it is often applied
nowadays to denote the fact that a something is actually “evolved” in
embryology--if only our entelechy had taken the place of the machine
of the mechanists. But that is the very point: there must be a real
“evolving” of a something, in order that the word evolution may be
justified verbally: and that is not the case in so-called phylogeny. At
least we know nothing of an evolutionary character in the problematic
pedigree of the organisms, as we shall see more fully hereafter. The
term “theory of descent” is therefore less open to objection than is the
usual English term. The word transformism, as used by the French, would
also be a very good title.

The theory of descent is the hypothetic statement that the organisms
are really allied by blood among each other, in spite of their
diversities.[143] The question about their so-called monophyletic
or polyphyletic origin is of secondary importance compared with the
statement of relationship in general.

[143] We prefer this unpretending definition of the theory of descent
to every other. As soon as one introduces into the definition the
concept of the “transmutability of species,” the term “species” would
require a special definition, and that would lead to difficulties which
it is unnecessary to deal with for our main purposes. It has been
remarked by Krašan, (*Ausichten und Gespräche über die individuelle und
specifische Gestaltung in der Natur*) and by several other writers,
that the problem of mutability or immutability of course relates to the
individuals in the first place. I should like to add to this remark that
the possibility must be admitted of the individuals being transmutable,
whilst the “species” are not transmutable at the same time, the line
of the “species” being a fixed order, through which the “individuals”
have to pass in the course of their generations. What is meant here
will become clearer, when we study the different possible aspects of
“phylogeny.”

There are two different groups of facts which have suggested the idea
of transformism: none of these facts can be said to be conclusive, but
there certainly is a great amount of probability in the whole if taken
together.

The first group of evidences which lead to the hypothesis of the real
relationship of organisms consists of facts relating to the geographical
distribution of animals and plants and to palæontology. As to geography,
it seems to me that the results of the floral and faunal study of groups
of islands are to be mentioned in the first place. If, indeed, on
each of the different islands, *A* *B* *C* and *D*, forming a group,
the species of a certain genus of animals or plants are different in a
certain respect, and show differences also compared with the species
living on the neighbouring continent, of which there is geological
evidence that the islands once formed a part, whilst there is no change
in the species on the continent itself for very wide areas, then, no
doubt, the hypothesis that all these differing species once had a common
origin, the hypothesis that there is a certain community among them all,
will serve to elucidate in some way what would seem to be very abstruse
without it. And the same is true of the facts of palaeontology. In
the geological strata, forming a continuous series, you find a set of
animals, always typical and specific for every single stratigraphical
horizon, but forming a series just as do those horizons. Would not the
whole aspect of these facts lose very much of its peculiarity if you
were to introduce the hypothesis that the animals changed with the
strata? The continuity of life, at least, would be guaranteed by such an
assumption.

The geographical and geological evidences in favour of the theory of
descent are facts taken from sciences which are not biology proper; they
are not facts of the living but only facts about the living. That is not
quite without logical importance, for it shows that not biology alone
has led to the transformism hypothesis. Were it otherwise, transformism
might be said to be a mere hypothesis *ad hoc*; but now this proves to
be not the case, though we are far from pretending that transformism
might be regarded as resting upon a real *causa vera*.

But let us study the second group of facts which support the theory of
descent. It is a group of evidences supplied by biology itself that we
meet here, there being indeed some features in biology which can be
said to gain some light, some sort of elucidation, if the theory of
descent is accepted. Of course, these facts can only be such as relate
to specific diversities, and indeed are facts of systematics; in other
words, there exists something in the very nature of the system of
organisms that renders transformism probable. The system of animals and
plants is based upon a principle which might be called the principle
of *similarities and diversities by gradation*; its categories are not
uniform but different in degree and importance, and there are different
kinds of such differences. No doubt, some light would be shed upon this
character of the system, if we were allowed to assume that the relation
between similarities and diversities, which is gradual, corresponded to
a blood-relationship, which is gradual also.

THE COVERT PRESUMPTION OF ALL THEORIES OF DESCENT

We have used very neutral and somewhat figurative words, in order to
show what might be called the logical value of the theory of descent,
in order to signify its value with respect to so-called “explanation.”
We have spoken of the “light” or the “elucidation” which it brings, of
the “peculiarity of aspect” which is destroyed by it. We have used this
terminology intentionally, for it is very important to understand that
a specific though hidden addition is made almost unconsciously to the
mere statement of the hypothesis of descent as such, whenever this
hypothesis is advocated in order to bring light or elucidation into any
field of systematic facts. And this additional hypothesis indeed must be
made from the very beginning, quite irrespective of the more detailed
problems of the law of transformism, in order that *any* sort of
so-called explanation by means of the theory of descent may be possible
at all. Whenever the theory that, in spite of their diversities, the
organisms are related by blood, is to be really useful for explanation,
it must necessarily be assumed in every case that the steps of change,
which have led the specific form *A* to become the specific form *B*,
have been such as only to change *in part* that original form *A*. That
is to say: the similarities between *A* and *B* must never have become
overshadowed by their diversities.

Only on this assumption, which indeed is a newly formed additional
subsidiary hypothesis, joined to the original hypothesis of descent in
general--a hypothesis regarding the very nature of transformism--only
on this almost hidden assumption is it possible to speak of any sort of
“explanation” which might be offered by the theory of transformism to
the facts of geography, geology, and biological systematics. Later on
we shall study more deeply the logical nature of this “explanation”; at
present it must be enough to understand this term in its quasi-popular
meaning.

What is explained by the hypothesis of descent--including the additional
hypothesis, that there always is a prevalence of the similarities
during transformism--is the fact that in palaeontology, in the groups
of island and continent faunae and florae taken as a whole, as well as
in the single categories of the system, the similarities exceed the
diversities. The *similarities* now are “explained”; that is to say,
they are understood as resting on but one principle: the similarities
are understood as being due to inheritance;[144] and now we have but one
problem instead of an indefinite number. For this reason Wigand granted
that the theory of descent affords what he calls a numerical reduction
of problems.

[144] It seems to me that my argument gives a broader logical basis
to the theory of descent than does that of G. Wolff (*Die Begründung
der Abstammungslehre*, München, 1907). Wolff starts from the concept
of organic teleology, and thus finds the only reason for accepting
the theory of transformism in the existence of so-called “rudimentary
organs”; these organs would form an obstacle to teleology if they could
not be regarded as inherited.

Understanding then what is explained by the theory of descent with its
necessary appendix, we also understand at once what is *not* elucidated
by it: the diversities of the organism remain as unintelligible as they
always were, even if we know that inheritance is responsible for what
is similar or equal. Now there can be no doubt that the diversities are
the more important point in systematics; if there were only similarities
there would be no problem of systematics, for there would be no system.
Let us be glad that there are similarities in the diversities, and that
these similarities have been explained in some way; but let us never
forget what is still awaiting its explanation. Unfortunately it has been
forgotten far too often.

THE SMALL VALUE OF PURE PHYLOGENY

And so we are led to the negative side of the theory of transformism,
after having discussed its positive half. The theory of descent as
such, without a real knowledge of the factors which are concerned in
transformism, or of the law of transformism, in other terms, leaves the
problem of systematics practically where it was, and adds really nothing
to its solution. That may seem very deplorable, but it is true.

Imagine so-called historical geology, without any knowledge of the
physical and chemical factors which are concerned in it: what would
you have except a series of facts absolutely unintelligible to you? Or
suppose that some one stated the cosmogenetic theory of Kant and Laplace
without there being any science of mechanics: what would the theory mean
to you? Or suppose that the whole history of mankind was revealed to
you, but that you had absolutely no knowledge of psychology: what would
you have but facts and facts and facts again, with not a morsel of real
explanation?

But such is the condition in which so-called phylogeny stands. If it
is based only on the pure theory of transformism, there is nothing
explained at all. It was for this reason that the philosopher Liebmann
complained of phylogeny that it furnishes nothing but a “gallery of
ancestors.” And this gallery of ancestors set up in phylogeny is not
even certain; on the contrary, it is absolutely uncertain, and very
far from being a fact. For there is no sound and rational principle
underlying phylogeny; there is mere fantastic speculation. How could it
be otherwise where all is based upon suppositions which themselves have
no leading principle at present? I should not like to be misunderstood
in my polemics against phylogeny. I fully grant you that it may be
possible in a few cases to find out the phylogenetic history of smaller
groups with some probability, if there is some palaeontological
evidence in support of pure comparative anatomy; and I also do not
hesitate to allow that such a statement would be of a certain value with
regard to a future discovery of the “laws” of descent, especially if
taken together with the few facts known about mutations. But it is quite
another thing with phylogeny on the larger scale. Far more eloquent than
any amount of polemics is the fact that vertebrates, for instance, have
already been “proved” to be descended from, firstly, the amphioxus;
secondly, the annelids; thirdly, the *Sagitta* type of worms; fourthly,
from spiders; fifthly, from *Limulus*, a group of crayfishes; and
sixthly, from echinoderm larvae. That is the extent of my acquaintance
with the literature, with which I do not pretend to be specially
familiar. Emil du Bois-Reymond said once that phylogeny of this sort is
of about as much scientific value as are the pedigrees of the heroes of
Homer, and I think we may fully endorse his opinion on this point.

HISTORY AND SYSTEMATICS

A few words should be devoted to the relations between history and
systematics in biology. Is there no contradiction between historical
development and a true and rational system which, we conceded, might
exist some day in biological sciences, even though it does not at
present? By no means. A totality of diversities is regarded from quite
different points of view if taken as the material of a system, and if
considered as realised in time. We have said that chemistry has come
very near to proper rational systematics, at least in some of its
special fields; but the compounds it deals with at the same time may
be said to have originated historically also, though not, of course,
by a process of propagation. It is evident at once that the geological
conditions of very early times prohibited the existence of certain
chemical compounds, both organic and inorganic, which are known at
present. None the less these compounds occupy their proper place in
the system. And there may be many substances theoretically known to
chemical systematics which have never yet been produced, on account
of the impossibility of arranging for their proper conditions of
appearance, and nevertheless they must be said to “exist.” “Existence,”
as understood in systematics, is independent of special space and of
special time, as is the existence of the laws of nature: we may speak of
a Platonic kind of existence here. Of course it does not contradict this
sort of ideal existence if reality proper is added to it.

Thus the problem of systematics remains, no matter whether the theory
of descent be right or wrong. There always remains the question about
the totality of diversities in life: whether it may be understood by
a general principle, and of what kind that principle would be. As,
in fact, it is most probably by history, by descent, that organic
systematics is brought about, it of course most probably will happen
some day that the analysis of the causal factors concerned in the
history will serve to discover the principle of systematics also.

Let us now glance at the different kinds of hypotheses which have been
established in order to explain how the descent of the organisms might
have been possible. We have seen that the theory of transformism alone
is not worth very much as a whole, unless at least a hypothetical
picture can be formed of the nature of the transforming factors: it is
by some such reasoning that almost every author who has defended the
theory of descent in its universality tries to account for the manner in
which organisms have acquired their present diversities.

2. THE PRINCIPLES OF DARWINISM

There is no need in our times and particularly in this country, to
explain in a full manner the theory known under the name of Darwinism.
All of you know this theory, at least in its outlines, and so we may
enter at once upon its analytic discussion. A few words only I beg
you to allow me as to the name of “Darwinism” itself. Strange to say,
Darwinism, and the opinion of Charles Darwin about the descent of
organisms, are two different things. Darwin, the very type of a man
devoted to science alone and not to personal interests,--Darwin was
anything but dogmatic, and yet Darwinism is dogmatism in one of its
purest forms. Darwin, for instance, gave the greatest latitude to the
nature of the variations which form the battleground of the struggle
for existence and natural selection; and he made great allowances for
other causal combinations also, which may come into account besides
the indirect factors of transformism. He was Lamarckian to a very
far-reaching extent. And he had no definite opinion about the origin
and the most intimate nature of life in general. These may seem to
be defects but really are advantages of his theory. He left open the
question which he could not answer, and, in fact, he may be said to be a
good illustration of what Lessing says, that it is not the possession
of truth but the searching after it, that gives happiness to man. It was
but an outcome of this mental condition that Darwin’s polemics never
left the path of true scientific discussions, that he never in all his
life abused any one who found reason to combat his hypotheses, and that
he never turned a logical problem into a question of morality.

How different is this from what many of Darwin’s followers have made out
of his doctrines, especially in Germany; how far is “Darwinism” removed
from Darwin’s own teaching and character!

It is to Darwinism of the *dogmatic* kind, however, that our next
discussions are to relate, for, thanks to its dogmatism, it has the
advantage of allowing the very sharp formulation of a few causal
factors, which *a priori* might be thought to be concerned in organic
transformism, though we are bound to say that a really searching
analysis of these factors ought to have led to their rejection from the
very beginning.

The logical structure of dogmatic Darwinism reveals two different parts,
which have nothing at all to do with one another.

NATURAL SELECTION

We shall first study that part of it which is known under the title
of natural selection, irrespective of the nature of the causes of
primary differences, or, in other words, the nature of variability.
This part may be said to belong to Darwin’s personal teachings and not
only to “Darwinism.” The offspring of a certain number of adults show
differences compared with each other; there are more individuals in the
offspring than can grow up under the given conditions, therefore there
will be a struggle for existence amongst them, which only the fittest
will survive; these survivors may be said to have been “selected” by
natural means.

It must be certain from the very beginning of analysis that natural
selection, as defined here, can only eliminate what cannot survive, what
cannot stand the environment in the broadest sense, but that natural
selection never is able to create diversities. It always acts negatively
only, never positively. And therefore it can “explain”--if you will
allow me to make use of this ambiguous word--it can “explain” only why
certain types of organic specifications, imaginable *a priori*, do
*not* actually exist, but it never explains at all the existence of the
specifications of animal and vegetable forms that are actually found. In
speaking of an “explanation” of the origin of the living specific forms
by natural selection one therefore confuses the sufficient reason for
the non-existence of what there is not, with the sufficient reason for
the existence of what there is. To say that a man has explained some
organic character by natural selection is, in the words of Nägeli, the
same as if some one who is asked the question, “Why is this tree covered
with these leaves,” were to answer “Because the gardener did not cut
them away.” Of course that would explain why there are no more leaves
than those actually there, but it never would account for the existence
and nature of the existing leaves as such. Or do we understand in the
least why there are white bears in the Polar Regions if we are told that
bears of other colours could not survive?

In denying any real explanatory value to the concept of natural
selection I am far from denying the action of natural selection. On
the contrary, natural selection, to some degree, is *self-evident*;
at least as far as it simply states that what is incompatible with
permanent existence cannot exist permanently, it being granted that
the originating of organic individuals is not in itself a guarantee of
permanency. Chemical compounds, indeed, which decompose very rapidly
under the conditions existing at the time when they originated may also
be said to have been eliminated by “natural selection.” It is another
question, of course, whether in fact all eliminations among organic
diversities are exclusively due to the action of natural selection in
the proper Darwinian sense. It has been pointed out already by several
critics of Darwinism and most clearly by Gustav Wolff, that there are
many cases in which an advantage with regard to situation will greatly
outweigh any advantage in organisation or physiology. In a railway
accident, for instance, the passengers that survive are not those who
have the strongest bones, but those who occupied the best seats; and
the eliminating effect of epidemics is determined at least as much by
localities, *e.g.* special houses or special streets, as by the degree
of immunity. But, certainly, natural selection is a *causa vera* in many
other cases.

We now may sum up our discussion of the first half of Darwinism.
Natural selection is a negative, an eliminating factor in transformism;
its action is self-evident to a very large degree, for it simply
states that things do not exist if their continuance under the given
conditions is impossible. To consider natural selection as a positive
factor in descent would be to confound the sufficient reason for the
non-existence of what is not, with the sufficient reason of what is.

Natural selection has a certain important logical bearing on
systematics, as a science of the future, which has scarcely ever been
alluded to. Systematics of course has to deal with the totality of the
possible, not only of the actual diversities; it therefore must remember
that more forms may be possible than are actual, the word “possible”
having reference in this connection to originating, not to surviving.
Moreover, systematics is concerned not only with what has been
eliminated by selection, but also with all that might have originated
from the eliminated types. By such reasoning natural selection gains a
very important aspect--but a logical aspect only.

FLUCTUATING VARIATION THE ALLEGED CAUSE OF ORGANIC DIVERSITY

The second doctrine of dogmatic Darwinism states that all the given
diversities among the organisms that natural selection has to work
upon are offered to natural selection by so-called fluctuating
variation; that is, by variation as studied by means of statistics.
This sort of variation, indeed, is maintained to be indefinite in
direction and amount, at least by the most conservative Darwinians; it
has occasionally been called a real differential; in any case it is
looked upon as being throughout contingent with regard to some unity
or totality; which, of course, is not to mean that it has not had a
sufficient reason for occurring.

It could hardly be said to be beyond the realm of possibility that such
differences among organic species as only relate to degree or quantity
and perhaps to numerical conditions also, might have been “selected” out
of given contingent variations, if but one postulate could be regarded
as fulfilled. This postulate may appropriately be stated as the fixation
of new averages of variation by inheritance. Let the average value of
a variation, with regard to a given property of a given species be *n*
and let the value *n* + *m*--*m* being variable--which is represented in
fewer individuals of course than is *n*, be such as to offer advantages
in the struggle for existence; then the individuals marked by *n* + *m*
will have the greater chance of surviving. Our postulate now states
that, in order that a permanent increase of the average value of the
variation in question may be reached, *n* + *m* in any of its variable
forms must be able to become the average value of the second generation,
as *n* was the average value of the first. Out of the second generation
again it would be the few individuals marked by *n* + *m* + *o*, which
would be selected; *n* + *m* + *o* would be the new average; afterwards
*n* + *m* + *o* + *p* would be selected, would become the new average,
and so on. A black variety for instance might be selected by such a
series of processes out of a grey-coloured one without difficulty.

But our postulate is not beyond all doubt: certain experiments, at
least, which have been carried out about the summation of variations
of the true fluctuating type by any kind of selection seem to show
that there may be a real progress for a few generations, but that this
progress is always followed by a reversion. Of course our experience
is by no means complete on this subject, and, indeed, it may be shown
in the future that positive transforming effects of fluctuating
variability, in connection with selective principles, are possible in
the case of new quantitative differences (in the widest sense), but we
are not entitled to say so at present.

And this is the only condition on which we can give credit to the second
doctrine of dogmatic Darwinism. Its second principle, indeed, proves
to be absolutely inadequate to explain the origin of any other kind of
specific properties whatever.

I cannot enter here into the whole subject of Darwinian criticism.[145]
Our aims are of a positive character, they desiderate construction
and only use destruction where it is not to be avoided. So I shall
only mention that dogmatic Darwinism has been found to be unable to
explain every kind of mutual adaptations, *e.g.* those existing between
plants and insects; that it can never account for the origin of those
properties that are indifferent to the life of their bearer, being mere
features of organisation as an arrangement of parts; that it fails in
the face of all portions of organisation which are composed of many
different parts--like the eye--and nevertheless are functional units
in any passive or active way; and that, last not least, it has been
found to be quite inadequate to explain the first origin of all newly
formed constituents of organisation even if they are not indifferent:
for how could any rudiment of an organ, which is not functioning at all,
not only be useful to its bearer, but be useful in such a degree as to
decide about life or death?

[145] See Wigand, *Der Darwinismus und die Naturforschung Newton’s und
Cuvier’s*, Braunschweig, 1874-7; Nägeli, *Mechanisch-physiologische
Theorie der Abstammungslehre*, München, 1884; G. Wolff, *Beiträge zur
Kritik der Darwin’schen Lehre*, 2nd ed. Leipzig, 1898; etc.

It is only for one special feature that I should like to show, by
a more full analysis, that dogmatic Darwinism does not satisfy the
requirements of the case. The special strength of Darwinism is said to
lie in its explaining everything that is useful in and for organisms;
the competitive factor it introduces does indeed seem to secure at least
a relative sort of adaptedness between the organism and its needs. But
in spite of that, we shall now see that Darwinism fails absolutely to
explain those most intimate organic phenomena which may be said to be
the most useful of all.

Darwinism in its dogmatic form is not able to explain the origin of any
sort of organic restitution; it is altogether impossible to account for
the restitutive power of organisms by the simple means of fluctuating
variation and natural selection in the struggle for existence. Here we
have the logical *experimentum crucis* of Darwinism.

Let us try to study in the Darwinian style the origin of the
regenerative faculty, as shown in the restitution of the leg of a
newt. All individuals of a given species of the newt, say *Triton
taeniatus*, are endowed with this faculty; all of them therefore must
have originated from ancestors which acquired it at some time or other.
But this necessary supposition implies that all of these ancestors must
have lost their legs in some way, and not only one, but all four of
them, as they could not have acquired the restitutive faculty otherwise.
We are thus met at the very beginning of our argument by what must be
called a real absurdity, which is hardly lessened by the assumption that
regeneration was acquired not by all four legs together, but by one
after the other. But it is absolutely inevitable to assume that *all*
the ancestors of our *Triton* must have lost one leg, or more correctly,
that only those of them survived which had lost one! Otherwise not all
newts at the present day could possess the faculty of regeneration! But
a second absurdity follows the first one; out of the ancestors of our
newt, which survived the others by reason of having lost one of their
legs, there were selected only those which showed at least a very small
amount of healing of their wound. It must be granted that such a step
in the process of selection, taken by itself, would not at all seem to
be impossible; since healing of wounds protects the animals against
infection. But the process continues. In every succeeding stage of it
there must have survived only those individuals which formed just a
little more of granulative tissue than did the rest: though *neither*
they themselves *nor* the rest could use the leg, which indeed was
not present! That is the second absurdity we meet in our attempt at a
Darwinian explanation of the faculty of regeneration; but I believe the
first one alone was sufficient.

If we were to study the “selection” of the faculty of one of the
isolated blastomeres of the egg of the sea-urchin to form a whole larva
only of smaller size, the absurdities would increase. At the very
beginning we should encounter the absurdity, that of all the individuals
there survived only those which were not whole but half; for *all*
sea-urchins are capable of the ontogenetical restitution in question,
*all* of their ancestors therefore must have acquired it, and they
could do that only *if* they became halved at first by some accident
during early embryology. But we shall not insist any further on this
instance, for it would not be fair to turn into ridicule a theory which
bears the name of a man who is not at all responsible for its dogmatic
form. Indeed, we are speaking against Darwinism of the most dogmatic
form only, not against Darwin himself. He never analysed the phenomena
of regeneration or of embryonic restitution--they lay in a field very
unfamiliar to him and to his time. I venture to say that if he had taken
them into consideration, he would have agreed with us in stating that
his theory was not at all able to cover them; for he was prepared to
make great concessions, to Lamarckism for instance, in other branches of
biology, and he did not pretend, to know what life itself is.

Darwin was not a decided materialist, though materialism has made
great capital out of his doctrines, especially in Germany. His book,
as is well known, is entitled “The Origin of *Species*,” that is of
organic *diversities*, and he himself possibly might have regarded all
restitution as belonging to the original properties of life, anterior to
the originating of diversities. Personally he might possibly be called
even a vitalist. Thus dogmatic “Darwinism” in fact is driven into all
the absurdities mentioned above, whilst the “doctrine of Darwin” can
only be said to be wrong on account of its failing to explain mutual
adaptation, the origin of new organs, and some other features in organic
diversities; the original properties of life were left unexplained by it
intentionally.

DARWINISM FAILS ALL ALONG THE LINE

The result of our discussion then must be this: selection has proved to
be a negative factor only, and fluctuating variation as the only way
in which new properties of the organisms might have arisen has proved
to fail in the most marked manner, except perhaps for a few merely
quantitative instances. Such a result betokens the complete collapse
of dogmatic Darwinism as a general theory of descent: the most typical
features of all organisms remain as unexplained as ever.

What then shall we put in the place of pure Darwinism? Let us first try
a method of explanation which was also adopted occasionally by Darwin
himself: let us study that form of transformation theories which is
commonly known under the title of Lamarckism.

3. THE PRINCIPLES OF LAMARCKISM.

As the word “Darwinism” does not signify the proper theoretical system
of Charles Darwin, so Lamarckism as commonly understood nowadays is a
good deal removed from the original views of Jean Baptiste Lamarck.
Lamarckism is generally regarded as reducing all organic diversities to
differences in the needs of individual life, but Lamarck himself, as
must be emphasised from the very beginning, did not at all maintain the
opinion that the great characteristics of the types were only due to
such accidental factors. He supposed a sort of law of organisation to
be at the root of systematics, as developed in history, and the needs
of life were only responsible, according to him, for splitting the
given types of organisation into their ultimate branches. Thus Lamarck,
to a great extent at any rate, belongs to a group of authors that we
shall have to study afterwards: authors who regard an unknown law of
phylogenetic development as the real basis of transformism. Modern
so-called Neo-Lamarckism, on the other hand, has indeed conceded the
principle of needs to be the sole principle of transformism. Let us then
study Lamarckism in its dogmatic modern form.

ADAPTATION AS THE STARTING-POINT

All facts of morphological adaptations--facts which we have analysed
already from a different point of view, as being among the most typical
phenomena of organic regulation--form the starting-point of this
theory, and it must be granted that they form a very solid foundation,
for they are facts. The theory only has to enlarge hypothetically the
realm of these facts, or rather the realm of the law that governs them.
Indeed, it is assumed by Lamarckism that the organism is endowed with
the faculty of responding to *any* change of the environment which may
change its function by a morphologically expressed alteration of its
functional state and form, which is adapted to the state of conditions
imposed from without. Of course, as stated in this most general form,
the assumption is not true, but it is true within certain limits, as
we know; and there seems to be no reason why we should not believe
that there are many more cases of adaptation than we actually know at
present, or that, in former phylogenetic times, the organisms were more
capable of active adaptation than they are now. So to a certain extent,
at least, Lamarckism can be said to rest upon a *causa vera*.

It is important to notice that this *causa vera* would imply vitalistic
causality when taken in the wide meaning which Lamarckism allows to
it: indeed, the power of active adaptation to indefinite changes would
imply a sort of causal connection that is nowhere known except in the
organism. Lamarck himself is not very clear about this point, he seems
to be afraid of certain types of uncritical vitalism in vogue in his
days; but modern writers have most clearly seen what the logical
assumptions of pure Lamarckism are. Next to Cope, August Pauly[146] may
be said to be the most conscious representative of a sort of so-called
psychological vitalism, which indeed Lamarckism as a general and
all-embracing theory must have as its basis.

[146] *Darwinismus und Lamarckismus*, München, 1905.

THE ACTIVE STORING OF CONTINGENT VARIATIONS AS A HYPOTHETIC PRINCIPLE

This point will come out more fully, if now we turn to study a certain
group of principles, upon which dogmatic Lamarckism rests: I say
principles and not facts, for there are no facts but only hypothetic
assumptions in this group of statements. We do know a little about
adaptations, at least to a certain extent, and it was only about the
sphere of the validity of a law, which was known to be at work in
certain cases, that hypothetical additions were made. In the second
group of the foundations of Lamarckism we know absolutely nothing;
accidental variations of form are supposed to occur, and the organism is
said to possess the faculty of keeping and storing these variations and
of handing them down to the next generation, if they happen to satisfy
any of its needs.

But these needs are not of the actual type, brought forth by a change of
the functional state of the individual, as in the case of adaptations:
they are of a somewhat mysterious nature. A glance at the theory of the
origin of the movements which are called acts of volition in the human
child may serve to elucidate what is meant.

Acts of volition are said thus to originate in random movements of the
new-born infant: certain of these accidental motions which happen to
relieve some pain or to afford some pleasure are “remembered,” and are
used another time quite consciously to bring forth what is liked or to
remove what is disliked. So much for the present on a very difficult
subject, which will occupy us next year at much greater length. It is
clear that at least three fundamental phenomena are concerned in this
theory of the origin of acts of volition: the liking and disliking, the
keeping in mind, and the volition itself. The real act of volition,
indeed, is always based upon a connection of all these factors, these
factors now being connected in such a way that even their kind of
connection may be said to be a fourth fundamental principle. In order
that the particular effect may be obtained which is wanted because it is
liked, the possible ways leading to it, which appeared among the random
movements in the very beginning, are now regarded as “means” and may now
be said to be “used.” But that is as much as to say that the “means”
are judged with respect to their usefulness for the actual purpose, and
therefore *judgment* is the fourth foundation of the act of volition.

In fact, Pauly does not hesitate to attribute judgment, along with the
other psychological elements, to the organisms whilst undergoing their
transformation. There has been formed, for instance, by accidental
variation some pigment which by its chemical nature brings the organism
into a closer connection with the light of the medium; the individual
likes that, keeps the pigment for itself and produces it again in the
next generation; and indeed it will safeguard any sort of improvement
which chance may effect in this primitive “eye.” Such a view is said
to hold well with respect to the origin of every new organ. And this
psychological argument is also said to afford the real explanation of
adaptation proper. Adaptation also is regarded not as a truly primary
faculty of the organism, but as a retention or provoking of metabolic
states which occurred by accident originally and were then found to
be useful; now they are reproduced either in every single case of
individual morphogenesis, without regard to actual requirements, or
else only in response to such: in the first case they are “inherited,”
in the second they only occur as regulations. Thus the process of
judgment, together with all the other elemental factors of psychical
life concerned in it, has been made to account for adaptation proper.
The whole theory has accordingly become very uniform and simple.

CRITICISM OF THE “INHERITANCE OF ACQUIRED CHARACTERS” ASSUMED BY
LAMARCKISM

In addressing ourselves to the criticism of Neo-Lamarckism we shall
neglect as far as possible all the different psychological principles
concerned in it--which in any case would need rather a great amount of
epistemological sifting--and shall keep to those hypothetic facts which
are supposed to be such as may be actually observed in nature.

All of you know that the so-called inheritance of acquired characters
lies at the root of Lamarckism; and from this hypothesis our critical
analysis is to start, disregarding a larger or smaller number of
psychological principles that are brought into the field.

The name of “acquired characters” may *a priori* be given to three
different types of phenomena: firstly, variations including mutations;
secondly, disease or injuries; and thirdly, the results of the actual
process of adaptation of every kind.

In the first of these groups, the true problem of the inheritance of
“acquired” characters appears only with certain restrictions. All
variations and mutations are indeed “acquired” by one generation so
far as the earlier generation did not possess them, but mutations, at
least, cannot be said to be acquired by the actual adult personality:
they are innate in it from its very beginning, and therefore may better
be called congenital.[147] Congenital properties of the mutation type
are, in fact, known to be inherited: their inheritance does not present
any problem of its own, but is included in the changes of the hereditary
condition to which they are due altogether.[148] All properties of the
variation type, on the other hand, having been studied statistically,
are known to be inherited, to a certain small extent, as we have seen
already whilst studying Darwinism, though they are possibly always
liable to reversion. Modern science, as we know,[149] regards them as
due to changes of nutrition, in the most general meaning of the word.
Under such a view variations might indeed be said to belong to the
acquired group of organic specifications; their inheritance, as will
be seen later on, would hardly be quite a pure instance of what we are
searching for. In no case can true variations claim to be of great
importance in problems of transformism.

[147] This would not be true, if the varieties of plants produced by
Blaringhem, Klebs, and MacDougal by means of *external* agents were
really “mutations” (comp. page 238, note 3).

[148] Of course, the inheritance of mutations would imply a certain sort
of “inheritance of acquired characters,” on the condition stated in the
preceding note. But, probably, the germs of the next generation might
be regarded here as being directly affected by the external agent, in a
manner that will briefly be mentioned later on in the text.

[149] Comp. page 238, note 2.

But what is known about the inheritance of those properties which
beyond any doubt may be said to have originated in the adult individual
as such, and of which lesions and adaptations proper, as shown for
instance among amphibious plants, are instances of the two most
typical groups?[150] Weismann did good service by putting an end to
the scientific credulity which prevailed with regard to this subject.
Weismann was led by his theory of the germ plasm to deny the inheritance
of acquired characters of the typical kinds. He could not imagine how
the effect of any agent upon the adult, be it of the merely passive or
of the adaptive kind, could have such an influence upon the germ as to
force it to produce the same effect in spite of the absence of that
agent. In fact, that is what the inheritance of acquired characters
would render necessary, and a very strange phenomenon it would be,
no doubt. But, of course, taken alone, it could never be a decisive
argument against such inheritance. I fully agree, that science is
obliged to explain new facts by what is known already, as long as it is
possible; but if it is no longer possible, the theory of course has to
be changed, and not the facts. On this principle one would not neglect
the fact of an inheritance of acquired properties, but on the contrary
one perhaps might use it as a new evidence of vitalism.

[150] Certain English authors have applied the term “modification” to
all kinds of organic properties acquired from without, whether they are
adapted or not.

But are there any facts?

At this point we come to speak about the second group of Weismann’s
reasonings. He not only saw the difficulty of understanding inheritance
of acquired characters on the principles of the science of his time,
but he also criticised the supposed facts; and scarcely any of them
stood the test of his criticism. Indeed, it must fairly be granted that
not one case is known which really proves the inheritance of acquired
characters, and that injuries certainly are never found to be inherited.
In spite of that, I do not believe that we are entitled to deny the
possibility of the inheritance of a certain group of acquired characters
in an absolute and dogmatic manner, for there are a few facts which seem
at least to tend in the direction of such an inheritance, and which seem
to show that it might be discovered perhaps one day, if the experimental
conditions were changed.

I am not referring here to the few cases in which bacteria were made
colourless or non-virulent by outside factors, or in which certain
fungi were forced to permanent agamic reproduction by abnormal external
conditions and were shown to retain their “acquired properties”
after the external conditions had been restored. In these cases only
reproduction by simple division occurred, and that does not imply the
true problem of inheritance. Nor am I referring to the few cases of
non-adaptive “modifications” found by Standfuss and Fischer, in which
butterflies that had assumed an abnormal kind of pigmentation under
the influence of abnormal temperature acting upon the pupa, were seen
to form this same kind of pigmentation in the next generation under
normal conditions of temperature. These cases, though important in
themselves, are capable perhaps of a rather simple explanation, as in
fact has been suggested. Some necessary means both of inheritance and of
morphogenesis, the former being present in the propagation cells, may
be said to have been changed or destroyed by heat, and therefore, what
seems to be inherited after the change of the body only, would actually
be the effect of a direct influence of the temperature upon the germ
itself.[151] Let me be clearly understood: I do not say that it is so,
but it may be so. What seems to me to be more important than everything
and to have a direct bearing on the real discovery of the inheritance
of acquired characters in the future, is this. In some instances
plants which had been forced from without to undergo certain typical
morphological adaptations, or at least changes through many generations,
though they did not keep the acquired characters permanently in spite
of the conditions being changed to another type, were yet found to lose
the acquired adaptations not suddenly but only in the course of three
or more generations. A certain fern, *Adiantum*, is known to assume a
very typical modification of form and structure, if grown on serpentine;
now Sadebeck,[152] while cultivating this serpentine modification of
*Adiantum* on ordinary ground, found that the first generation grown in
the ordinary conditions loses only a little of its typical serpentine
character, and that the next generation loses a little more, so that
it is not before the fifth generation that all the characters of the
serpentine modification have disappeared. There are a few more cases
of a similar type relating to plants grown in the plains or on the
mountains. There also it was found to take time, or rather to take the
course of *several* generations, until what was required by the new
conditions was reached. Of course these cases are very very few compared
with those in which a *sudden* change of the adaptive character,
corresponding to the actual conditions, sets in; but it is enough that
they do exist.

[151] Of course the inheritance of specific values from the results of
fluctuating variations, leading to new averages of variability (see
p. 265), may also be understood in this manner, the conditions of
nourishment acting upon the adult and upon its germs equally well.

[152] *Berichte üb. d. Sitzung. d. Ges. f. Bot.*, Hamburg, 1887, 3 Heft.

Would it not be possible at least that adaptations which last
for thousands of generations or more might in fact change the
adaptive character into a congenital one? Then we not only should
have inheritance of acquired characters, but should have a sort
of explanation at the same time for the remarkable fact that
certain histological structures of a very adapted kind are formed
ontogenetically before any function exists, as is known to be the
case with the structures in the bones of vertebrates, for instance.
Experiments are going on at Paris, and perhaps in other places of
scientific research also, which, it is hoped, will show that animals
reared in absolute darkness for many generations will lose their
perfectly formed eyes, and that animals from the dark with very
rudimentary eyes will be endowed with properly functioning ones, after
they have been reared in the light for generations. Such a result indeed
would account for the many animals, of the most different groups, which
live in dark caves and possess only rudiments of eyes: functional
adaptation is no longer necessary, so-called atrophy by inactivity sets
in, and the results “acquired” by it are inherited.[153]

[153] Quite recently Kammerer (*Arch. Entw. Mech.* 25, 1907, p. 7) has
published very important experiments on the inheritance of “acquired”
modifications with regard to the peculiarities of reproduction in
*Salamandra atra* and *S. maculosa*. It seems rather improbable--though
not absolutely impossible--that the germ cells were directly affected by
the external modifying agent in this case.

But enough of possibilities. Let us be content at present to know at
least a few real instances with regard to the slowness of the process of
what might be said to be “re-adaptation” in some plants. This process
shows us a way by which our problem may some day be solved; it allows
us to introduce inheritance of acquired characters as a legitimate
hypothesis at least, which not only will explain many of the diversities
in systematics historically, but also can be called, though not a *causa
vera*, yet certainly more than a mere fiction.

OTHER PRINCIPLES WANTED

We have only dealt with the probability of the inheritance of
morphological or physiological[154] adaptation. If that could really be
considered as one of the factors concerned in the theory of descent,
many, if not all of those congenital diversities among organic species
which are of the type of a true structural correspondence to their
future functional life, might be regarded as explained, that is,
as reduced to one and the same principle. But nothing more than an
explanation of *this* kind of diversities is effected by our principle,
and very much more remains to be done, for organic diversities not only
consist in specifications and differences as to histology, but are to a
much more important degree, differences of organisation proper, that is,
of the arrangement of parts, in the widest sense of the word.[155]

[154] We have not spoken about the hypothetic inheritance of pure
physiological adaptations, for it is clear without further discussion
that innate specific immunity, for instance, being a specific
“adaptedness” (*see* p. 186) *might* be due to the inheritance of the
results of active immunity as an adaptation, just as adaptive congenital
structures *might* be due to such an inheritance.

[155] C. E. v. Baer clearly discriminated between the type, the degree
of organisation, and the histological structure. All these three topics
indeed have to be taken into account separately; the third alone is of
the adaptive type. All of them may be independent of each other: the
Amoeba may be as adapted histologically as is a high vertebrate, but it
is of much lower type; and in its own type it is of a lower degree of
organisation than Radiolaria are.

Would it be possible to interpret the origin of this sort of systematic
diversities by a reasoning similar to that by which we have understood,
at least hypothetically, congenital adaptedness?

Dogmatic Lamarckism, we know, uses two principles as its foundations;
one of them, adaptation and its inheritance, we have studied with what
may be called a partly positive result. The other is the supposed
faculty of the organism to keep, to store, and to transfer those
variations or mutations of a not properly adaptive sort which, though
originating by chance, happen to satisfy some needs of the organism.

CRITICISM OF THE HYPOTHESIS OF STORING AND HANDING DOWN CONTINGENT
VARIATIONS

Strange to say, this second hypothesis of dogmatic Lamarckism, invented
with the express purpose of defeating Darwinism and taking the place of
its fluctuating variability, which was found not to do justice to the
facts--this second hypothesis of dogmatic Lamarckism is liable to just
the same objections as dogmatic Darwinism itself.

As it is important to understand well the real logical nature of
our objections to both of the great transformistic theories, we
think it well to interrupt our argument for a moment, in order to
consider a certain point which, though very important in itself,
seems of only secondary importance to us in our present discussion.
Dogmatic Darwinism--I do not say the doctrine of Charles Darwin--is
materialistic at bottom, and indeed has been used by many to complete
their materialistic view of the universe on its organic side. The word
“materialism” must not necessarily be taken here in its metaphysical
sense, though most materialists are dogmatic metaphysicians. It also
can be understood as forming part of a phenomenological point of view.
Materialism as a doctrine of science means simply this: that whether
“nature” be reality or phenomenon, in any case there is but one ultimate
principle at its base, a principle relating to the movements of
particles of matter. It is this point of view which dogmatic Darwinism
strengthens; on the theory of natural selection and fluctuating
variations, due to accidental differences of nutrition, organisms are
merely arrangements of particles of matter, nothing else; and moreover,
their kinds of arrangement are understood, at least in principle.
Lamarckism, on the other hand, is not materialistic, but most markedly
vitalistic--psychistic even; it takes life for granted when it begins
its explanations.

You may tell me that Darwin did the same, that he expressly states that
his theory has nothing to do with the origin of life; that the title
of his work is “The Origin of *Species*.” It would certainly be right
to say so, at least with reference to Darwin personally; but in spite
of that, it must be granted that Darwin’s doctrine contains a certain
germ of materialism which has been fully developed by the Darwinian
dogmatists, while Lamarckism is antimaterialistic by its very nature.

Now it is very important, I think, to notice that this difference
between the two theories is unable to disguise one main point which is
common to both: and it is to this point, and to this point only, that
our chief objections against both these theories converge at present.

The *contingency* of the typical organic form is maintained by Darwinism
as well as by Lamarckism: both theories, therefore, break down for
almost the same reasons. The term “contingency” can signify very
different relations, having but little in common; but it is sufficient
for our present purpose to observe that there may be distinguished
roughly two main classes of contingencies, which may provisionally be
called the “contingency of being,” and the “contingency of occurring.”
It is with the contingency of being that criticism of Darwinism and
Lamarckism of the dogmatic type has to deal. Darwinism dealt with
variations occurring at random; the organic form was the result of
a fixation of only one kind of such variations, all others being
extinguished by selection. In other terms, the specific organised
form, as understood by Darwinism, was a unit only to the extent that
all its properties related to one and the same body, but for the rest
it was a mere aggregation or summation. It may be objected to this
statement, that by being inherited in its specificity the Darwinian
form proved to be a unit in a higher sense of the word, even in the
opinion of dogmatic Darwinians; and this objection, perhaps, holds good
as far as inheritance is concerned. But on the other hand, it must
never be forgotten that the word “unit” had quite a vague and empty
meaning even then, as indeed everything the organism is made up of
is regarded as being in itself due to a contingent primary process,
which has no relation to its fellow-processes. “Unit,” indeed, in spite
of inheritance--which, by the way, is alleged also to be a merely
materialistic event--means to Darwinians no more when applied to the
organism than it does when applied to mountains or islands, where of
course a sort of “unit” also exists in some sense, as far as one and the
same body comes into account, but where every single character of this
unit, in every single feature of form or of quality, is the result of
factors or agents each of which is independent of every other.

To this sort of contingency of being, as maintained by Darwinians,
criticism has objected, as we know, that it is quite an impossible
basis of a theory of descent, since it would explain neither the first
origin of an organ, nor any sort of harmony among parts or among whole
individuals, nor any sort of restitution processes.

Now Lamarckism of the dogmatic kind, as will easily be seen, only
differs from Darwinism in this respect, that what according to the
latter happens to the organism passively by means of selection, is
according to the former performed actively by the organism, by means of
a “judgment”--by the retention and handing down of chance variations.
The specificity of the form as a whole is contingent also according
to Lamarckism. And, indeed, criticism must reject this contingency of
being in exactly the same way as it rejected the contingency of form
maintained by Darwinians.

As far as the inheritance of truly adaptive characters comes into
account--that is, the inheritance of characters which are due to the
active faculty of adaptation possessed by the organism, bearing a
vitalistic aspect throughout--hardly anything could be said against
Lamarckism, except that inheritance of acquired characters is still
an hypothesis of small and doubtful value at present. But that
*specific organisation proper* is due to *contingent* variations, which
accidentally have been found to satisfy some needs of the individual and
therefore have been maintained and handed down, this reasoning is quite
an impossibility of exactly the same kind as the argument of Darwinism.

The process of restitution, perfect the very first time it occurs, if it
occurs at all, is again the classical instance against this new sort of
contingency, which is assumed to be the basis of transformism. Here we
see with our eyes that the organism can do more than simply perpetuate
variations that have occurred at random and bear in themselves no
relation whatever to any sort of unit or totality. There *exists* a
faculty of a certain higher degree in the organism, and this faculty
cannot possibly have originated by the process which Lamarckians[156]
assume. But if their principle fails in one instance, it fails as a
*general* theory altogether. And now, on the other hand, as we actually
see the individual organism endowed with a morphogenetic power,
inexplicable by Lamarckism, but far exceeding the organogenetic faculty
assumed by that theory, would it not be most reasonable to conclude from
such facts, that there exists a certain organising power at the root of
the transformism of species also, a power which we do not understand,
which we see only partially manifested in the work of restitutions,
but which certainly is not even touched by any of the Lamarckian
arguments? There does indeed exist what Gustav Wolff has called primary
purposefulness (“primäre Zweckmässigkeit”), at least in restitutions,
and this is equally unexplainable by Darwinism and by the dogmatism of
the Lamarckians.

[156] I repeat once more that we are dealing here with dogmatic
“Neo-”Lamarckism exclusively. This theory indeed claims to explain *all*
features and properties of organic bodies on the basis of the feeling
of needs and storing of contingent fulfilments and on this basis alone,
just as dogmatic “Neo”-Darwinism claims to account for *all* those
phenomena on the ground of contingent variations and natural selection.
Darwin himself, as we have seen, intentionally left unexplained certain
primary features of life and therefore cannot be blamed for having
failed to explain them, though even then his theory remains wrong.
Lamarck personally considered a real primary organisatory law of
phylogeny as being of fundamental importance, and therefore he is not in
the least responsible if “Neo-Lamarckism” fails as a universal theory.

But before entering into this area of hypothesis, let us mention a few
more objections to be made to the theory of the contingency of form as
put forward by Lamarckians. In the first place, let us say a few words
about the appropriateness of the term “contingency” as used in this
connection. The forms are regarded as contingent by Lamarckians inasmuch
as the variations which afterwards serve as “means” to the “needs” of
the organism occur quite accidentally with regard to the whole organism.
It might be said that these “needs” are not contingent but subject
to an inherent destiny, but this plea is excluded by the Lamarckians
themselves, when they say that the organism experiences no need until it
has enjoyed the accidental fulfilment of the same. So the only thing in
Lamarckian transformism which is not of a contingent character would be
the psychological agent concerned in it, as being an agent endowed with
the primary power of feeling needs after it has felt fulfilment, and of
judging about what the means of future fulfilment are, in order to keep
them whenever they offer. But these are characteristics of life itself,
irrespective of all its specific forms, which alone are concerned in
transformism. Now indeed, I think, we see as clearly as possible that
Darwinism and Lamarckism, in spite of the great contrast of materialism
and psychologism, shake hands on the common ground of the contingency of
organic forms.

The whole anti-Darwinistic criticism therefore of Gustav Wolff for
instance, may also be applied to Lamarckism with only a few changes
of words. How could the origin of so complete an organ as the eye of
vertebrates be due to contingent variations? How could that account for
the harmony of the different kinds of cells in this very complicated
organ with each other and with parts of the brain? And how is it to be
understood, on the assumption of contingency, that there are two eyes of
almost equal perfection, and that there are two feet, two ears? Islands
and mountains do not show such symmetry in *their* structures.

We shall not repeat our deduction of the origin of restitutions, of
regeneration for instance, on the dogmatic Lamarckian theory. As we
have said already, it would lead to absurdities as great as in the
case of dogmatic Darwinism, and indeed we already have mentioned that
Lamarckians would hardly even attempt to explain these phenomena.
It follows that dogmatic Lamarckism fails as a general theory about
form.[157]

[157] Compare also the excellent criticism of Lamarckism lately given by
G. Wolff, *Die Begründung der Abstammungslehre*, München, 1907.

There is finally one group of facts often brought forward against
Lamarckism by Darwinian authors[158] which may be called the logical
*experimentum crucis* of this doctrine, an *experimentum* destined
to prove fatal. You know that among the polymorphic groups of bees,
termites, and ants, there exists one type of individuals, or even
several types, endowed with some very typical features of organisation,
but at the same time absolutely excluded from reproduction: how could
those morphological types have originated on the plan allowed by the
Lamarckians? Of what use would “judgment” about means that are offered
by chance and happen to satisfy needs, be to individuals which die
without offspring? Here Lamarckism becomes a simple absurdity, just as
Darwinism resulted in absurdities elsewhere.

[158] It has also very often been said by Darwinians that Lamarckism is
only able to explain those cases of adaptedness which relate to active
functioning but not mere passive adapted characters, like “mimicry” for
example. But this argument *taken by itself*, it seems to me, would not
be fatal to Neo-Lamarckism in the special form August Pauly gave to this
doctrine.

We were speaking about dogmatic Darwinism then, and it is about dogmatic
Lamarckism that we are reasoning at present; both theories must fall in
their dogmatic form, though a small part of both can be said to stand
criticism. But these two parts which survive criticism, one offered by
Lamarck, the other by Darwin, are far from being a complete theory of
transformism, even if taken together: they only cover a small area of
the field concerned in the theory of descent. Almost everything is still
to be done, and we may here formulate, briefly at least, what we expect
to be accomplished by the science of the future.

4. THE REAL RESULTS AND THE UNSOLVED PROBLEMS OF TRANSFORMISM

What has been explained to a certain extent by the two great theories
now current is only this. Systematic diversities consisting in mere
differences as to intensity or number may perhaps owe their origin to
ordinary variation. They may at least, if we are entitled to assume
that heredity in some cases is able to hand on such variations without
reversion, which, it must be again remarked, is by no means proved by
the facts at present. Natural selection may share in this process by
eliminating all those individuals that do not show the character which
happens to be useful. That is the Darwinian part of an explanation of
transformism which may be conceded as an hypothesis. On the other side,
congenital histological adaptedness may be regarded hypothetically as
due to an inheritance of adaptive characters which had been acquired by
the organism’s activity, exerted during a great number of generations.
That is the Lamarckian part in the theory of descent.

But nothing more is contributed to this theory either by the doctrine
of Darwin or by that of Lamarck. So it follows that almost everything
has still to be done; for no hypothesis at present accounts for
the foundation of all systematics, viz., for the differences in
organisation, in all that relates to the so-called types as such and
the degree of complication in these types, both of which (types and
degree of complication) are independent of histological adaptation and
adaptedness.

What then do we know about any facts that might be said to bear on
this problem? We have stated already at the end of our chapter devoted
to the analysis of heredity that what we actually know about any
deviation of inheritance proper, that is, about congenital differences
between the parents and the offspring, relating to mere tectonics,
is practically nothing: indeed, there are at our disposal only the
few facts observed by de Vries or derived from the experience of
horticulturalists and breeders. We may admit that these facts at
least prove the possibility[159] of a discontinuous variation, that
is of “mutation,” following certain lines of tectonics and leading to
*constant* results; but everything else, that is everything about a real
theory of phylogeny, must be left to the taste of each author who writes
on the theory of the Living. You may call that a very unscientific state
of affairs, but no other is possible.

[159] But nothing more. All “mutations” hitherto observed in nature
or (comp. page 238, note 3) experimentally produced relate only to
“varieties” and not to “species.” One could hardly say that the
recent investigations about the production of mutations by *external*
means have strengthened their importance for the general theory of
transformism.

And, in fact, it has been admitted by almost all who have dealt with
transformism without prepossessions that such is the state of affairs.
Lamarck himself, as we have mentioned already, was not blind to the fact
that a sort of organisatory law must be at the base of all transformism,
and it is well known that hypothetical statements about an original law
of phylogeny have been attempted by Nägeli, Kölliker, Wigand, Eimer,
and many others. But a full discussion of all these “laws” would hardly
help us much in our theoretical endeavour, as all of them, it must be
confessed, do little more than state the mere fact that some unknown
principle of organisation must have been at work in phylogeny, if we are
to accept the theory of descent at all.

It is important to notice that even such a convinced Darwinian as
Wallace, who is well known to have been an independent discoverer of the
elimination principle, admitted an exception to this principle in at
least one case--with regard to the origin of man. But one exception of
course destroys the generality of a principle.

As we ourselves feel absolutely incapable of adding anything specific
to the general statement that there *must* be an unknown principle of
transformism, if the hypothesis of descent is justified at all, we may
here close our discussion of the subject.

5. THE LOGICAL VALUE OF THE ORGANIC FORM ACCORDING TO THE DIFFERENT
TRANSFORMISTIC THEORIES

A few words only must be added about two topics: on the character of
organic forms as regarded by the different transformistic theories, and
on the relation of transformism in general to our concept of entelechy.

We have learnt that both Darwinism and Lamarckism, in their dogmatic
shape, regard the specific forms of animals and plants as being
contingent; in fact, it was to this contingency that criticism was
mainly directed. We therefore are entitled to say that to Darwinism and
Lamarckism organic forms are accidental in the very sense of the *forma
accidentalis* of the old logicians. There are indefinite forms possible,
according to these theories, and there is no law relating to these
forms. Systematics, under such a view, must lose, of course, any really
fundamental importance. “There is no rational system about organisms”:
that is the ultimate statement of Darwinism and of Lamarckism on this
doubtful question. Systematics is a mere catalogue, not at present
only, but for ever, by the very nature of the organisms. It is not
owing to the indefinite number of possible forms that both our theories
came to deny the importance of systematics, but to the want of a *law*
relating to this indefinite number: among chemical compounds indefinite
possibilities also exist in some cases, but they obey the law of the
general formula. It is very strange that Darwinians of all people are
in the forefront of systematic research in all countries: do they not
see that what they are trying to build up can only relate to accidental
phenomena? Or have they some doubts about the foundations of their own
theoretical views, in spite of the dogmatic air with which they defend
them? Or is it the so-called historical interest which attracts them?

A new question seems to arise at this point: Have not we ourselves
neglected history in favour of systematics and laws? Our next lecture,
the last of this year, will give the answer to this question.

At present we continue our study of the possible aspects of systematics.
It is not difficult to find out what meaning organic forms would assume
under any phylogenetic theory opposed to the theories of contingency.
It was their defence of contingency, that is, their lack of any law
of forms, that caused these theories to be overthrown--reduced to
absurdities even--and therefore, it follows that to assume any kind of
transformistic law is at the same time to deny the accidental character
of the forms of living beings.

There is no *forma accidentalis*. Does that mean that the *forma
essentialis* is introduced by this mere statement? And what would *that*
assert about the character of systematics?

THE ORGANIC FORM AND ENTELECHY

This problem is not as simple as it might seem to be at the first
glance, and, in fact, it is insoluble at present. It is here that the
relation of the hypothetic transformistic principle to our concept of
entelechy is concerned.

We know that entelechy, though not material in itself, uses material
means in each individual morphogenesis, handed down by the material
continuity in inheritance. What then undergoes change in phylogeny,
the means or the entelechy? And what would be the logical aspect of
systematics in either case?

Of course there would be a law in systematics in any case; and therefore
systematics in any case would be rational in principle. But if the
transformistic factor were connected with the means of morphogenesis,
one could hardly say that specific form as such was a primary essence.
Entelechy would be that essence, but entelechy in its generality and
always remaining the same in its most intimate character, as the
specific diversities would only be due to a something, which is not
form, but simply means to form. But the *harmony* revealed to us in
every typical morphogenesis, be it normal or be it regulatory, seems
to forbid us to connect transformism with the means of morphogenesis.
And therefore we shall close this discussion about the most problematic
phenomena of biology with the declaration, that we regard it as more
congruent to the general aspect of life to correlate the unknown
principle concerned in descent with entelechy itself, and not with
its means. Systematics of organisms therefore would be in fact
systematics of entelechies, and therefore organic forms would be
*formae essentiales*, entelechy being the very essence of form in its
specificity. Of course systematics would then be able to assume a truly
rational character at some future date: there might one day be found
a principle to account for the totality of possible[160] forms, a
principle based upon the analysis of entelechy.[161] As we have allowed
that Lamarckism hypothetically explains congenital adaptedness in
histology, and that Darwinism explains a few differences in quantity,
and as such properties, of course, would both be of a contingent
character, it follows that our future rational system would be combined
with certain accidental diversities. And so it might be said to be
one of the principal tasks of systematic biological science in the
future to discover the really rational system among a given totality of
diversities which cannot appear rational at the first glance, one sort
of differences, so to speak, being superimposed upon the other.

[160] The word “possible” relating to originating, of course, not to
surviving. It is here that natural selection may acquire its logical
importance alluded to above (see page 264).

[161] The discussions in the second volume of this book will show the
possible significance of such an analysis. We at present are dealing
with entelechy in a quasi-popular manner.

*C.* THE LOGIC OF HISTORY

History, in the strictest sense of the word, is the enumeration of the
things which have followed one another in order of time. History deals
with the single, with regard both to time and space. Even if its facts
are complex in themselves and proper to certain other kinds of human
study, they are nevertheless regarded by history as single. Facts, we
had better say, so far as they are regarded as single, are regarded
historically, for what relates to specific time and space is called
history.

Taken as a simple enumeration or registration, history, of course,
cannot claim to be a “science” unless we are prepared to denude that
word of all specific meaning. But that would hardly be useful. As a
matter of fact, what has actually claimed to be history, has always
been more than a mere enumeration, even in biology proper. So-called
phylogeny implies, as we have shown, that every one of its actual
forms contains some rational elements. Phylogeny always rests on
the assumption that only some of the characters of the organisms
were changed in transformism and that what remained unchanged may be
explained by the fact of inheritance.

But this, remember, was the utmost we were able to say for phylogeny.
It remains fantastic and for the most part unscientific in spite of
this small degree of rationality, as to which it is generally not very
clear itself. For nothing is known with regard to the positive factors
of transformism, and we were only able to offer the discussion of a few
possibilities in place of a real theory of the factors of descent.

In spite of that it will not be without a certain logical value to begin
our analysis of history in general by the discussion of possibilities
again. Biology proper would hardly allow us to do more: for the
simple “fact” of history is not even a “fact” in this science, but an
hypothesis, albeit one of some probability.

As discussions of mere possibilities should always rest on as broad a
basis as possible, we shall begin our analysis by raising two general
questions. To what kinds of realities may the concept of history
reasonably be applied? And what different types of “history” would be
possible *a priori*, if the word history is to signify more than a mere
enumeration?

1. THE POSSIBLE ASPECTS OF HISTORY

Of course, we could select one definite volume in space and call all the
consecutive stages which it goes through, its history: it then would be
part of its history that a cloud was formed in it, or that a bird passed
through it on the wing. But it would hardly be found very suggestive to
write the history of space-volumes. In fact, it is to *bodies* in space
that all history actually relates, at least indirectly, for even the
history of sciences is in some respect the history of men or of books.
It may suffice for our analysis to understand here the word body in its
popular sense.

Now in its relation to bodies history may have the three following
aspects, as far as anything more than a simple enumeration comes into
account. Firstly, it may relate to one and the same body, the term
body again to be understood popularly. So it is when the individual
history of the organism is traced from the egg to the adult, or when the
history of a cloud or of an island or of a volcano is written. Secondly,
the subject-matter of history may be formed by the single units of a
consecutive series of bodies following each other periodically. To this
variety of history the discoveries of Mendel and his followers would
belong in the strictest sense, but so does our hypothetical phylogeny
and a great part of the history of mankind. And lastly, there is a
rather complicated kind of sequence of which the “history” has actually
been written. History can refer to bodies which are in no direct
relation with one another, but which are each the effect of another body
that belongs to a consecutive series of body-units showing periodicity.
This sounds rather complicated; but it is only the strict expression
of what is perfectly familiar to you all. Our sentence indeed is
simply part of the definition of a history of art or of literature for
instance--or, say, of a phylogenetic history of the nests of birds. The
single pictures are the subjects of the history of art, and nobody would
deny that these pictures are the effects of their painters, and that
the painters are individuals of mankind--that is, that they are bodies
belonging to a consecutive series of body-units showing periodicity. Of
course, it is only improperly that we speak of a history of pictures or
of books or of nests. In fact, we are dealing with painters, and with
men of letters or of science, and with certain birds, and therefore
the third type of history may be reduced to the second. But it was not
without value to pursue our logical discrimination as far as possible.

So far we have always spoken of history as being more than a mere
enumeration, but we have not ascertained what this “more” signifies. It
is not very difficult to do so: in fact, there are three different types
of history, each of a different degree of importance with respect to the
understanding of reality.

In the first place, history may start as a mere enumeration at the
beginning, and at the end, in spite of all further endeavour, may
*remain* that and nothing more. That may occur in the first as well
as in the second group of our division of history with regard to
its relation to bodies. Take a cloud and describe its history from
the beginning to the end: there would never be much more than pure
description. Or take one pair of dogs and describe them and their
offspring for four generations or more: I doubt if you will get beyond
mere descriptions in this case either. The only step beyond a mere
enumeration which we can be said to have advanced in these instances,
consists in the conviction, gained at the end of the analysis, that
nothing more than such an enumeration is in any way *possible*.

Quite the opposite happens when “history” deals with the individual
from the egg to the adult: here the whole series of historical facts is
seen to form one whole. This case therefore we shall call not history,
but *evolution*, an evolving of something; the word “evolution” being
understood here in a much wider sense than on former occasions,[162] and
*including*, for instance, the embryological alternative “evolutio” or
“epigenesis.”

[162] See pp. 26, 45, 54, etc.

And half-way between enumeration and evolution there now stands a type
of history which is more than the one and less than the other: there is
a kind of intelligible connection between the consecutive historical
stages and yet the concept of a whole does not come in. The geological
history of a mountain or of an island is a very clear instance of this
class. It is easy to see here, how what *has been* always becomes the
foundation of what *will be* in the *next* phase of the historical
process. There is a sort of *cumulation* of consecutive phases, the
later ones being impossible without the earlier. So we shall speak
of the type of “historical cumulation” as standing between evolution
and bare temporal sequence. By means of historical cumulations history
may fairly claim to “explain” things. We “understand” a mountain or an
island in all its actual characteristics, if we know its history. This
“historical understanding” rests on the fact that what first appeared
as an inconceivable complex has been resolved into a sequence of single
events, each of which may claim to have been explained by actually
existing sciences. The complex has been explained as being, though not
a real “whole,” yet a sum of singularities, every element of which is
familiar.

But you may tell me that my discussion of evolution and of cumulation,
as the higher aspects of history, is by no means complete; nay,
more--that it is altogether wrong. You would certainly not be mistaken
in calling my analysis incomplete. We have called one type of history
evolution, the other cumulation; but how have these higher types been
reached? Has historical enumeration itself, which was supposed to
stand at the beginning of all analysis, or has “history” itself in its
strictest sense, as relating to the single as such, risen unaided into
something more than “history”? By no means: history has grown beyond
its bounds by the aid of something from without. It is unhistorical
elements that have brought us from mere history to more than history.
We have created the concept of evolution, not from our knowledge of the
single line of events attendant on a single egg of a frog, but from our
knowledge that there are billions or more of frogs’ eggs, all destined
to the same “history,” which therefore is not history at all. We have
created the concept of cumulation not from the historical study of
a single mountain, but from our knowledge of physics and chemistry
and so-called dynamical geology: by the aid of these sciences we
“understood” historically, and thus our understanding came from another
source than history itself.

2. PHYLOGENETIC POSSIBILITIES

Does history always gain its importance from what it is not? Must
history always lose its “historical” aspect, in order to become of
importance to human knowledge? And can it *always* become “science” by
such a transformation? We afterwards shall resume this discussion on
a larger scale, but at present we shall apply what we have learned to
hypothetic phylogeny. What then are the possibilities of phylogeny, to
what class of history would it belong if it were complete? Of course, we
shall not be able to answer this question fully; for phylogeny is *not*
complete, and scarcely anything is known about the factors which act
in it. But in spite of that, so much, it seems to me, is gained by our
analysis of the possible aspects of history and of the factors possibly
concerned in transformism, that we are at least able to formulate the
possibilities of a phylogeny of the future in their strict logical
outlines.

Darwinism and Lamarckism, regarding organic forms as contingent, must
at the same time regard organic history as a cumulation; they indeed
*might* claim to furnish an historical explanation in the realm of
biology--if only their statements were unimpeachable, which as we have
seen, they are not.

But any transformistic theory, which locates the very principle of
phylogeny in the organism itself, and to which therefore even organic
forms would be not accidental but essential, might be forced to regard
the descent of organisms as a true evolution. The singularities in
phylogenetic history would thus become links in one whole: history
proper would become more than history. But I only say that phylogeny
*might* be evolution, and in fact I cannot admit more than this *a
priori*, even on the basis of an internal transformistic principle,
as has been assumed. Such a principle also might lead always from one
typical state of organisation to the next: but *ad infinitum*.[163]
Then phylogeny, though containing what might in some sense be called
“progress,” would not be “evolution”; it might even be called cumulation
in such a case, in spite of the internal transforming principle, though,
of course, cumulation from within would always mean something very
different from cumulation from without.[164]

[163] An immanent vitalistic phylogeny *without* a pre-established end
has recently been advocated by H. Bergson (*L’évolution créatrice*,
Paris, 1907).

[164] In this connection the problem may be raised, whether there can be
such a thing as unchangeable “species” in spite of the mutability of the
individuals. Compare page 251, note 1.

But we must leave this problem an open question, as long as our actual
knowledge about transformism remains as poor as it is. We need only add,
for the sake of logical interest, that phylogeny, as a true evolution,
would necessarily be characterised by the possibility of being repeated.

3. THE HISTORY OF MANKIND

We only assume hypothetically that phylogeny has happened, and we know
scarcely anything about the factors concerned in it. Now, it certainly
would be of great importance, if at least in a small and definite field
of biology we were able to state a little more, if the *mere fact* of
phylogeny, of “history,” were at least beyond any doubt within a certain
range of our biological experience. And indeed there is one department
of knowledge, where history, as we know, *has happened*, and where we
also know at least some of the factors concerned in it.

I refer to the history of mankind; and I use the expression not at all
in its anthropological or ethnographical sense, as you might expect
from a biologist, but in its proper and common sense as the history of
politics and of laws and of arts, of literature and of sciences: in a
word, the history of civilisation. Here is the only field, where we know
that there actually *are* historical facts: let us try to find out what
these facts can teach us about their succession.

The theory of history in this narrower meaning of the word has been
the subject of very numerous controversies in the last twenty years,
especially in Germany, and these controversies have led very deeply into
the whole philosophical view of the universe. We shall try to treat our
subject as impartially as possible.

Hegel says, in the introduction to his *Phänomenologie des Geistes*:
“*Die Philosophie muss sich hüten erbaulich sein zu wollen*”
(“Philosophy must beware of trying to be edifying”). These words,
indeed, ought to be inscribed on the lintel of the door that leads
into historical methodology, for they have been sadly neglected by
certain theoretical writers. Instead of analysing history in order to
see what it would yield to philosophy, they have often made philosophy,
especially moral philosophy, the starting-point of research, and history
then has had to obey certain doctrines from the very beginning.

We shall try as far as we can not to become “erbaulich” in our
discussions. We want to learn from history for the purposes of
philosophy, and we want to learn from history as from a phenomenon in
time and in space, just as we have learnt from all the other phenomena
regarding life in nature. Every class of phenomena of course may
be studied with respect to generalities as well as with respect to
particulars. The particular, it is true, has not taught us much in our
studies so far. Perhaps it may be successful in the domain of history
proper.

If I take into consideration what the best authors of the last century
have written about human history with respect to its general value, I
cannot help feeling that none of them has succeeded in assigning to
history a position where it would really prove to be of great importance
for the aims of philosophical inquiry. Is that the fault of the authors
or of human history? And what then would explain the general interest
which almost every one takes, and which I myself take in history in
spite of this unsatisfactory state of things?

CUMULATIONS IN HUMAN HISTORY

Let us begin our analytical studies of the value and the meaning of
human history, by considering some opinions which deserve the foremost
place in our discussion, not as being the first in time, but as being
the first in simplicity. I refer to the views of men like Buckle, Taine,
and Lamprecht, and especially Lamprecht, for he has tried the hardest to
justify theoretically what he regards the only scientific aim of history
to be. If we may make use of our logical scheme of the three possible
aspects of history, it is clear from the beginning that the history of
mankind, as understood by the three authors we have named, but most
particularly by Lamprecht, is neither a mere enumeration nor a true
evolution, but that it has to do with *cumulations*, in the clearest
of their possible forms. The processes of civilisation among the
different peoples are in fact to be compared logically with the origin
of volcanoes or mountain-ranges in Japan, or in Italy, or in America,
and show us a typical series of consecutive phases, as do these. There
exists, for instance, in the sphere of any single civilisation an
economic system, founded first on the exchange of natural products,
and then on money. There are, or better, perhaps, there are said to
be, characteristic phases succeeding one another in the arts, such as
the “typical,” the “individualistic,” and the “subjective” phases. Any
civilisation may be said to have its “middle ages,” and so on. All these
are “laws” of course in the meaning of “rules” only, for they are far
from being elemental, they are not “principles” in any sense. And there
are other sorts of “rules” at work for exceptional cases: revolutions
have their rules, and imperialism, for instance, has its rules also.

Now, as the consecutive phases of history have been shown to be
true cumulations, it follows that the rules which are revealed by
our analysis, are rules relating to the very origin of cumulations
also. The real *element* upon which the cumulation-phases, and the
cumulation-rules together rest, is the human individual as the bearer
of its psychology. Nobody, it seems to me, has shown more clearly than
Simmel that it is the human individual, *qua* individual, which is
concerned in *every* kind of history.

History, viewed as a series of cumulations, may in fact claim to
satisfy the intellect by “explaining” a good deal of historical facts.
It explains by means of the elemental factor of individual psychology,
which every one knows from himself, and by the simple concept that there
is a cumulation, supported by language and by writing as its principal
factors, which both of course rest on psychology again. Psychology,
so we may say, is capable of leading to cumulation phenomena; the
cumulations in history are such that we are able to understand them by
our everyday psychology; and history, so far as it is of scientific
value, consists exclusively of cumulations.

No doubt there is much truth in such a conception of history; but
no doubt also, it puts history in the second rank as compared with
psychology; just as geology stands in the second rank as compared with
chemistry or physics. Geology and human history may lead to generalities
in the form of rules, but these rules are *known* to be not elemental
but only cumulative; and moreover, we know the elements concerned in
them. The elements, therefore, are the real subjects for further studies
in the realm of philosophy, but not the cumulations, not the rules,
which are known to be due to accidental constellations. Of course, the
“single” is the immediate subject of this sort of history, but the
single as such is emphatically pronounced to be insignificant, and the
cumulations and the cumulative rules, though “singles” in a higher sense
of the word, are shown to be anything but elementalities.

Therefore, on a conception of human history such as that of Buckle,
Taine, Lamprecht, and others, we, of course, ought to take an interest
in history, because what is “explained” by historical research touches
all of us most personally every day and every year. But our philosophy,
our view of the world, would remain the same without history as it is
with it. We only study history, and especially the history of our own
civilisation, because it is a field of actuality which directly relates
to ourselves, just as we study for practical purposes the railway
time-tables of our own country, but not of Australia; just as we study
the local time-table in particular.

If the mere *rerum cognoscere causas* is regarded as the criterium of
science, history of Lamprecht’s type of course is a science, for its
explanations rest upon the demonstration of the typical constellations
and of the elemental factor or law from which together the next
constellations are known necessarily to follow. But history of this kind
is not a science in the sense of discovering *den ruhenden Pol in der
Erscheinungen Flucht*.

HUMAN HISTORY NOT AN “EVOLUTION”

Quite another view of history has been maintained by Hegel, if his
explanations about the *Entwicklung des objectiven Geistes* (“the
development of the objective mind”) may be co-ordinated with our
strictly logical categories of the possible aspects of history. But I
believe we are entitled to say that it was a real *evolution* of mankind
that Hegel was thinking of; an evolution regarding mankind as spiritual
beings and having an end, at least ideally. One psychical state was
considered by Hegel to generate the next, not as a mere cumulation
of elemental stages, but in such a way that each of the states would
represent an elementality and an irreducibility in itself; and he
assumed that there was a continuous series of such stages of the mind
through the course of generations. Is there any sufficient reason in
historical facts for such an assumption?

The mind “evolves” itself from error to truth by what might be called
a system of contradictions, according to Hegel, with respect to logic
as well as to morality; the sum of such contradictions becoming smaller
and less complicated with every single step of this evolution. No doubt
there really occurs a process of logical and moral refining, so to say,
in the individual, and no doubt also, the results of this process,
as far as attained, can be handed down to the next generation by the
spoken word or by books. But it is by no means clear, I think, that this
process is of the type of a real evolution towards an end, so far as it
relates to the actual series of generations as such. On the contrary,
it seems to me that we have here simply what we meet everywhere in
history--a sort of cumulation resting upon a psychological basis.

The dissatisfaction that exists at any actual stage of contradiction,
both moral and logical, is one of the psychical factors concerned;
the faculty of reasoning is the other. Now it is a consequence of the
reasoning faculty that the dissatisfaction continually decreases, or
at least changes in such a way that each partial result of the logical
process brings with it the statement of new problems. The number of
such problems may become less, as the logical process advances, and,
indeed, there is an ideal state, both logical and moral, in which there
are no more problems, but only results, though this ideal could hardly
be regarded as attainable by the *human* mind. In the history of those
sciences which are wholly or chiefly of the *a priori* type, this
process of deliverance from contradictions is most advantageously to
be seen. It is obvious in mechanics and thermodynamics, and the theory
of matter is another very good instance. A certain result is reached;
much seems to be gained, but suddenly another group of facts presents
itself, which had been previously unknown or neglected. The first result
has to be changed or enlarged; many problems of the second order arise;
there are contradictions among them, which disappear after a certain
alteration of what was the first fundamental result, and so on. And the
same is true about morality, though the difficulties are much greater
here, as a clear and well-marked standard of measurement of what is good
and what is bad, is wanting, or at least, is not conceded unanimously.
But even here there is a consensus on some matters: one would hardly go
back to slavery again, for instance, and there are still other points
in morality which are claimed as ideals at least by a great majority of
moral thinkers.

But all this is not true “evolution,” and indeed, I doubt if such an
evolution of mankind could be proved at present in the sense in which
Hegel thought it possible. The process of logical and moral deliverance
from contradictions *might* come to an end in *one* individual; at least
that is a logical possibility, or it might come to an end in, say,
six or ten generations. And there is, unfortunately for mankind, no
guarantee that the result will not be lost again and have to be acquired
a second time. All this proves that what Hegel regarded as an evolution
of the race is only a cumulation. There is nothing evolutionary relating
to the generations of mankind as such. At least, nothing is proved about
such an evolution.[165]

[165] On account of the limited size of the earth a certain final stage
of human civilisation might be expected in a future time; but it would
be the size of the earth which determined this end, and not the process
of civilisation itself.

You may call my view pessimistic, and indeed you may be right so far
as the sum total of human beings as such is in question. But, be it
pessimistic or not, we are here moving on scientific ground only, and
have merely to study the probability or improbability of problematic
facts, and with such a view in our mind, we are bound to say that a
true logical and moral evolution of mankind is not at all supported
by known facts. There is a process of logical and moral perfection,
but this process is *not one*, is not “single” in its actuality; it is
not connected with the one and single line of history, but only with a
few generations each time it occurs, or even with one individual, at
least ideally. And this process is not less a process of cumulation
than any other sort of development or so-called “progress” in history
is. Philosophers of the Middle Ages, in fact, sometimes regarded human
history as *one* evolutionary unity, beginning with the Creation and
ending with the Day of Judgment; but every one must agree, I think,
that even under the dogmatic assumptions of orthodoxy history would by
no means *necessarily* be an “evolution.” Even then the paths taken by
different individuals or different branches of the human race on their
way to redemption *can* be regarded as independent lines.

Thus Hegel’s conception of an evolution of mankind, it seems to me,
fails to stand criticism. By emphasising that there are certain lines of
development in history which bring with them a stimulus to perfection,
and that these lines relate to all that is highest in culture, Hegel
certainly rendered the most important service to the theory of history;
but in spite of that he has revealed to us only a special and typical
kind of cumulation process, and nothing like an evolution. We may say
that the very essence of history lies in this sort of cumulation, in
this “pseudo-evolution” as we might say; and if we like to become moral
metaphysicians we might add, that it is for the sake of the possibility
of this sort of cumulation that man lives his earthly life; the Hindoos
say so, indeed, and so do many Christians. But even if we were to depart
from our scientific basis in this way we should not get beyond the realm
of cumulations.

All this, of course, is not to be understood to affirm that there never
*will* be discovered any real evolutionary element in human history--in
the so-called “subconscious” sphere perhaps--but at present we
certainly are ignorant of such an element.

THE PROBLEM OF THE “SINGLE” AS SUCH

If history has failed to appear as a true evolution, and if, on the
other hand, it reveals to us a great sum of different cumulations, some
of very great importance, others of minor importance, what then remains
of the importance of the single historical event in its very singleness?
What importance can the description of this event have with regard to
our scientific aims? We could hardly say at present that it appears to
be of very much importance at all. The historical process as a whole
has proved to be not a real elemental unit, as far as we know, and such
elemental units as there are in it have proved to be of importance only
*for* individual psychology but not *as* history. History has offered
us only instances of what every psychologist knew already from his own
experience, or at least might have known if he had conceived his task in
the widest possible spirit.

But is no other way left by which true history might show its real
importance in spite of all our former analysis? Can history be saved
perhaps to philosophical science by any new sort of reasoning which we
have not yet applied to it here.

As a matter of fact, such new reasoning has been tried, and
Rickert,[166] in particular, has laid much stress upon the point
that natural sciences have to do with generalities, while historical
sciences have to do with the single in its singleness only, and, in
spite of that, are of the highest philosophical importance. He does not
think very highly of so-called “historical laws,” which must be mere
borrowings from psychology or biology, applied to history proper, and
not touching its character as “history.” We agree with these statements
to a considerable extent. But what then about “history proper,” what
about “the single in its very singleness”?

[166] *Die Grenzen der naturwissenschaftlichen Begriffsbildung*,
Tübingen and Leipzig, 1902.

Let us say at first a few words about this term “single” so very often
applied by us. In the ultimate meaning of the word, of course, the
series of actual sensations or “presentations” is the “single” which is
given “historically” to each individual, and therefore to the writer of
history also, and in fact, history as understood by Rickert is based
to a great extent upon this primordial meaning of single “givenness.”
The word “single,” in his opinion, relates to the *actual and true
specification* of any event, or group of events, at a given time and
at a given locality in space, these events possessing an identity of
their own and never being repeated without change of identity. If the
subject-matter of history is defined like this, then there are, indeed,
“Grenzen der naturwissenschaftlichen Begriffsbildung” with regard to
history, for natural sciences have nothing to do with the single in such
an understanding of the word.

Rickert says somewhere that history as a real evolution, as one
totality of a higher order, would cease to be proper history: and he
is right. History, in fact, would soon lose the character of specific
attachment to a given space and to a given time, and would lose its
“non-repeatability,” in the logical sense at least, if it were one
*unit* in reality: as soon as it was that, it would have become a
logical generality, an element in nature, so to say, in spite of its
factual singularity. But history is not obliged to become that, Rickert
states; and we may add that history in fact cannot become that, because
it simply proves not to be an evolution as far as we know at present.

But what importance does Rickert attach to his history specified and
non-repeatably single?

History has a logic of its own, he says; the scheme of its logic is not
the syllogism, but the *relation to “values.”* So far as the single
historical facts can be related to values, they are of historical
importance, and in such a way only does history in its proper sense
become important in itself and through itself at the same time. Must
history always lose its historical aspect to become of importance to
human knowledge? That is the question we asked whilst considering the
general logical types of the “evolution” and “cumulation” that arose out
of the analysis of the historical facts of problematic phylogeny. It
now might seem that this question may be answered, and that it may be
answered by a clear and simple “No.” The history of mankind, according
to Rickert, seems to be important in itself, and without borrowing from
any other branch of study. But is his reasoning altogether cogent and
convincing?

Has it really been able to attribute to history in the strictest sense
such an importance for philosophy, for the theory of the universe, “für
die Weltanschauung,” that history proper may in fact be allowed to take
its place beside science proper?

The relation to values is not to include any kind of “Bewertung” of
judgment, Rickert allows. In fact, history of any kind would hardly
satisfy the reader, if moral judgment were its basis. Every reader, of
course, has a moral judgment of his own, but, unfortunately, almost
every reader’s judgment is different from his neighbour’s, and there
is no uniformity of moral principles as there is of geometrical ones.
We shall come back to this point. At present we only state the fact
that indeed moral judgment can never be the foundation of history, and
that Rickert was very right to say so: it is enough to put the names
of Tolstoy and Nietzsche together to understand how devoid of even
the smallest general validity would be a history resting upon moral
principles.

But what then are the “values” of Rickert to which history has to
relate, if moral values in their proper sense have to be excluded? It is
here that his discussions begin to become obscure and unsatisfactory,
and the reason is fairly intelligible. He is trying to prove the
impossible; he wants to put history beside science in its real
philosophical importance, in spite of the fact that all evidence to
establish this is wanting.

These “values,” to which every historical act in its singularity has to
be related in order to become an element of real history, are they after
all nothing but those groups of the products of civilisation which in
fact absorb the interest of men? Is it to groups of cultural phenomena,
such as arts, science, the State, religion, war, economics, and so on,
that “historical” facts have to be related? Yes, as far as I understand
our author, it is simply to these or other even less important groups
of cultural effects--cultural “cumulations,” to apply our term--that a
single action of a man or a group of men must bear some relation in
order to become important historically.

But what does that mean? Is the relation to such “values” to be
regarded as really rendering history equal to the sciences of nature in
philosophical importance?

In the first place, there is no more agreement about such “values” than
there is in the field of morals. Imagine, for instance, a religious
enthusiast or recluse writing history! I fancy there would be very
little mention of warriors and politicians: war and politics would
not be “values” in *any* sense to such a man. And we know that there
are others to whom those products of civilised life rank amongst the
first. Rickert well notes that there is one great objection to his
doctrine--the character of universality[167] is wanting to his history,
or rather to the values forming its basis; for there cannot be, or at
least there actually is not at present, a *consensus omnium* with regard
to these “values.”

[167] The word “universality” to be understood here in quite an
unpretentious quasi-popular meaning, not strictly epistemologically.

I am convinced that Rickert is right in his conception of real “history”
as the knowledge of the single acts of mankind. But this conception
proves just the contrary of what Rickert hoped to prove; for history in
this sense is moulded by the actual products of culture, that is, by
the effects which actually exist as groups of cultural processes, and
it cannot be moulded by anything else; the historian correlates history
with what *interests* him personally.

Here now we have met definitively the ambiguous word: history indeed
is to end in “interest” and in being “interesting.” There is nothing
like a real “value” in any sense underlying history; the word *value*
therefore would better give place to the term “centre of interest”--a
collection of stamps may be such a “centre.” History, then, as the
knowledge of cultural singularities, is “interesting,” and its aspects
change with the interests of the person who writes history: there is no
commonly accepted foundation of history.[168]

[168] To avoid mistakes I wish to say here most emphatically that,
according to Rickert, the method of history is regarded as completely
*free* from subjectivity as soon as its “values” are once *established*.
But this cannot avail to save the theory.

And it follows that history as regarded by Rickert cannot serve as
the preliminary to philosophy. It *may* be[169] of use for personal
edification or for practical life: granting that the “centres of
interest” as referred to are of any real ethical or at least factual
importance. But you may take away from history even the greatest
personalities, and your view of the universe, your philosophy, would
remain the same, except of course so far as these personalities
themselves have contributed to philosophy in any way.

[169] This is a rather optimistic conception of “history.” Personally, I
must confess that even its emotional and practical importance seems to
me to be at least diminished by the retarding effects which all sorts
of “historical” considerations--in science as well as in arts and in
public life--carry with them. All real progress is non-historical--and
its champions almost always have become martyrs: this fact seems not to
recommend history as a means of education, except for persons of a very
strong character.

Now, on the other hand, it is worth noticing that, even if there were
generally accepted “values,” history as the doctrine of singularities
would be deprived of philosophical importance. Its single cases would
then be merely *instances* of certain types of actions and occurrences
which have been proved to be “valuable,” *i.e.* to be centres of
interest, before-hand. Rickert has observed that the relation to
any judgments about moral values would render history unhistorical,
for the generalities to which it is related would be the main thing
in such a case. But he did not notice, as far as I can see, that
history, if related to *any* “values” whatever--if there were any
generally conceded--would become “non-historical” just as well: for the
*generalities* as expressed in the “values” would be the main thing in
this case also. In fact, there is no escape from the dilemma:--either no
general centres of interest, and therefore a mere subjective “history”;
or general “values,” and therefore history a mere collection of
instances.

The “limits of concepts in natural sciences” then are the same as the
limits of *intellectual* concepts in general. For intellectual, *i.e.*
logical, “values” are the only centres of interest that can lay claim
to universality. There are indeed other groups of important concepts,
the ethical ones, but they are outside intellectuality and may enter
philosophy only as problems, not as solutions. Therefore, history in
its true sense, even if related to the ethical group of concepts,
has no bearing on philosophy. Philosophically it remains a sum of
contingencies, in which certain laws of cumulation and certain series of
cumulation may be discovered. But these series and these laws, if taken
scientifically, only offer us instances of psychological elementalities.
They also might be instances of primary ethical states and relations, if
there were such relations of more than a mere subjective and personal
validity, which at present at least seems not to be the case.

CONCLUSIONS ABOUT SYSTEMATICS AND HISTORY IN GENERAL

We have finished our analysis of the history of mankind as the only
instance of an historical biological process that is actually known to
exist and is not only assumed hypothetically.

What we have learnt from this analysis, though certainly important in
itself, has not afforded us any new result for theoretical biology.

The history of mankind is proved to be of philosophical importance,
at present, so far only as it offers instances to the science of
psychology; besides that it may be of value and importance to many
conditions of practical and emotional life.

There is only one science, and only one kind of logic too. “In one sense
the only science”--that was the predicate attached to natural sciences
by Lord Gifford, as you will remember from our first lecture. It is not
without interest to note that at the end of our course of this year,
we find occasion to realise on what a deep insight into logical and
philosophical relations that sentence was grounded.

We now leave the theory of human history, which has been to us nothing
more than a branch of biological phylogeny in general. We have dealt
with it from quite a simple realistic point of view, not burdened by any
epistemology. We have taken psychical states as realities, just as we
have taken as realities all parts of the animal body; and it seems to
me that we were entitled to do so, as it was only history *about* the
actions of men we were dealing with, not their actions themselves. Next
summer we shall begin with studying action as action, and then, in fact,
a well-founded epistemology will be among our first requirements. And
history also will come on the scene once more.

It is the main result of our last chapters, devoted to systematics,
transformism, and human history in particular, that no conclusions
really useful for further philosophical discussion can at present be
gained from these topics; there either is too little actual knowledge,
or there are only combinations of natural elementalities, but no
elementalities of any new kind.

To sum up: we expected that a rational system might be a biological
result of the future, but we could not claim at all to possess such a
system. We said that transformism might be proved one day to be a true
evolution, governed by one immanent principle, which then would have to
be regarded as a new primary factor in nature, but we did not know the
least about that principle.

Human history, on the other hand--that is, the only historical process
concerned with life that is actually known to have occurred--could not
teach us anything of an elemental character, since human history, at
present at least, did not appear to us as a true evolution, but only as
a sum of cumulations, and the singularities of this history, taken by
themselves, could only be of practical or emotional interest.

Thus it is from the study of the living *individual* only, that we
have so far gained elemental principles in biology. The analysis of
individual morphogenesis and of individual inheritance has yielded
us the concept of entelechy as the chief result of the first part of
our lectures. We shall be able to get more proofs of the autonomy of
the individual life in the beginning of the second part; indeed, the
beginning of that part will bring us to a full understanding of what the
living individual is, and what it is not. And then the real philosophy
of life, that is, the philosophy of the individual, will occupy us for
the greater half of our lectures of next summer.

INDEX

Absolute, 5

Acclimatisation, 191

Acquired characters, 217, 276 f.

Adaptation (definition), 166, 171, 185
to changes from without, 172 ff.
functional, 114, 176 ff.
and Lamarckism, 272, 280
mechanical, 177 f.
morphological, 168 ff.
physiological, 184 ff.
primary and secondary, 188 f.

Adaptedness, 186 f.

*Adiantum*, 279

Adventitious, 55, 74, 111, 221

Albumen, 200

Allelomorphs, 231

Amphibious plants, 172 ff.

Annelids, 65, 70, 221

Answering reaction, 181

Anti-bodies, 206 f.

Antitoxins, 207 f.

*A priori*, 6

Aristotle, 144

*Ascaris*, 93

*Aspergillus*, 195

Assimilation, 17

Atrophy, 178

Autonomy of life, 143, 224 f., 324

Babák, 177

Baer, C. E. v., 48 f. 282

Bateson, 229 ff., 238

Bayliss, 204, 212

*Begonia*, 221

Bergson, 305

Berkeley, 6

Berthold, 91

Biogenetisches Grundgesetz, 248

Biology, 8 ff., 15 f.

Blaringhem, 238, 276

Blastoderm, 39

Blastomeres, 36, 59, 61 f., 79

Blastula, 37, 61, 79

Blumenbach, 26

Boirivant, 174

Bonnet, 26

Boveri, 29, 60, 95, 235 f.

Buckle, 308, 310

Bunge, v., 248

Bütschli, 91

Calcium, 97

Calkins, 33

Cambium, 120, 183, 220

Catalysis, 164, 203

Categories, 6 f.

Cause, 99 ff.

Cell, 27 f.
-division, 28 ff., 53, 94
-lineage, 58, 70
-theory, 27 f.

Chemical theory (of morphogenesis), 134 ff.

Chemistry, systematics of, 244.

Child, C. M., 180

Chromatic regulations, 197

Chromatin, 28 f.

Chromosomes, 30, 237

Chun, 66

Classification, 246 f.

*Clavellina*, 129, 154, 162 f.

Cleavage, 35 ff., 53, 58, 60, 63, 71, 92

Colloids, 187

Compensatory process, 112

Complex potencies, 112, 120

Conic sections, 243

Conjugation, 33

Conklin, 86

Contingency, 218, 284 ff. 304

Continuity of germ-plasm, 215, 227

Cope, 273

Correlation (of masses), 93
(of parts), 247

Correns, 228

Crampton, 70 f.

Crayfish, 105

Ctenophores, 66

Cumulation, 301 ff., 308 ff., 314, 317

Cuvier, 247

Darwin, Ch., 260 ff., 271, 283

Darwinism, 260 ff., 271, 283 ff., 293 ff., 304

Davenport, 191, 206

Delage, 32

Descent, theory of, 250 ff.

Description, 12, 50

Detto, 172

Directive stimuli, 102 ff.

Doncaster, 232

Dreyer, 92

*Echinus*, 27, 33 ff., 60 ff., 68, 81, 85, 87,
98, 104, 108, 111, 154, 232, 235

Ectoderm, 41, 81, 122

Egg, 31, 33 f.

Ehrlich, 207 f.

Eimer, 292

Elementary organs, 46 ff.
processes, 46 ff.

Elements of nature, 9

Embryo, 44
frog’s, 59, 65, 67
half, 59, 61, 66 ff.
whole, 61, 67 f.

Endoderm, 41, 81

Entelechy, 143 f., 224 f., 295

Entwickelungsmechanik, 57, 70, 78, 241

Enumeration, 297, 300

Enzymes, 164, 203

Epigenesis, 26, 45, 54, 72, 144, 301

Equifinality (of restitutions), 159 f.

Equipotential, 83

Eschenhagen, 195

Evolutio, 26, 45 f., 54, 59, 61, 64, 72, 144, 205, 301

Evolution, 8, 21, 46, 250, 301, 305, 311 ff., 317

Experience, 7 f., 12, 212

Experiment, 51, 56 f.

“Explaining,” 51, 309

Explicit potency, 84

Fasting, 199 f.

Ferments, 164, 203 f.

Fertilisation, 32 ff.

Fischer, 278

Foges, 107

Form, closed or open, 49

Form, organic, specific, 16 ff., 25, 92, 293 ff.

Forma accidentalis, 293
essentialis, 294 f.

Formative stimuli, 102 ff., 113, 118, 133

Francé, 158, 239

Frédéricq, 196

Frog, embryo of, 59, 65, 67

Fromm, 205

Function (mathematical), 80

Fungi, metabolism of, 201

Gaidukow, 197 f.

Galls, 101

Galton, 228, 238

Gamble and Keeble, 198

Gastrula, 41, 61, 81

Gautier, 239

Geographical distribution, 251 f.

Geometry, solid, 243

Germ-layers, 41, 44, 61
-lineage, 215
-plasm, 52, 215

Gifford, Lord, 1 ff., 322

Godlewski, 105, 155, 235

Goebel, 116

Goethe, 247

Goette, 48, 56, 214

Goltz, 181

Growth, 30, 93 f.

Gruber, 236

Haeckel, 37, 41

Half-embryo, 59, 61, 66 ff.

Haller, A. v., 26

Harmony, 107 ff., 117, 295

Hausmann, 206

Heat production, 193

Hegel, 307, 311 ff.

Herbst, 96 ff., 102, 104 ff., 172, 177, 200, 232, 236

Heredity, 21, 52

Hering, 216 f.

Hertwig, O., 60, 65

Hertwig, R., 32 f., 60, 107

His, 56, 93

History, 2, 14, 21, 250, 257, 297 ff.
of mankind, 306 ff.

Holmes, 180

Hume, 6

Hypertrophy, 112, 114

Hypertypy, 112

Idealism, 5, 7

Immunity, 204 ff.

Implicit potency, 84

Improvement (of morphogenesis), 212

Indifferent cells, 182

Inflammation, 206

Inheritance, 35, 214 ff.
of acquired characters, 217, 275 ff., 290

Irritability, 190 ff.

Jacoby, 207

Jaeger, 214

Jennings, 218

Kammerer, 176, 280

Kant, 6 f.

Kirchhoff, 50

Klebs, 96, 170, 180, 238, 276

Kölliker, 292

Korshinsky, 239

Krašan, 221, 251

Lamarck, 271 f., 291

Lamarckism, 271 f., 284 ff., 293 ff., 304

Lamprecht, 308, 310

Larva, 41 f., 44

Law of nature, 13, 16

Leibniz, 6

Lens (of eye), 105, 221

Liebmann, 256

Life, 9 f., 16, 21

Lillie, R. S., 236

Limits of regulability, 212

Lithium, 99

“Living,” 9, 16

Localisation, 101, 103, 118 ff.

Locke, 6

Loeb, J., 32, 102, 164, 179, 196, 236

Loeb, L., 208

Lyon, 87

MacDougal, 238 f., 276

Machine (definition), 139

Machine-theory of life, 138 ff., 187, 210

Maillard, 196

Manifoldness, 25 f., 30, 45
intensive, 144

Materialism, 283

Materials, transport of, 194

Matter, theory of, 8

Maturation, 31, 87

Mayenburg, v., 195

Means, of morphogenesis, 89 ff., 101, 113, 118, 228, 234

Memory, 216 f.

Mendel, 229 f.

Merrifield, 198

Mesenchyme, 39, 41, 104, 111, 151 f.

Metabolic regulations, 198 f.

Metabolism, 16, 184
of fungi, 201

Metschnikoff, 206

Micromeres, 36, 60

Miehe, 116

Mill, J. S., 57

*Mimosa*, 191

Minkiewicz, 198

Modification, 277

Molluscs, 70 f., 86

Morgan, T. H., 32, 66 f., 95, 107, 114 f., 162, 230

Morphaesthesia, 157

Morphogenesis, 20, 52, 76, 112, 118 f.

Morphology, 12

Movements, organic, 17

Mutations, 237 f., 276, 291

Nägeli, 266, 292

Nathansohn, 196

Natural selection, 261 f., 290

Nature, 5 ff.

Němec, 116

Newport, 57

Newt (regeneration of), 155, 221 f.

Noll, 146, 157 f.

Nomothetic, 14 f.

Normal, 78

Nuclear division, 28 f., 62, 64 f., 72, 235

Nucleus, 28, 35
rôle of nucleus in inheritance, 233 f.

Organ-forming substances, 117

*Oscillariae*, 197

Osmotic pressure, 93, 187, 194 f.

Overton, 196 f.

Oxidation, rôle of, 198 f.

Palaeontology, 252

Parallelism (psycho-physical), 146

Parthenogenesis, 32

Pauly, 146, 217, 273 f.

Pawlow, 204, 210, 212

Pearl, R., 212

Pfeffer, 195, 201

Phagocytosis, 206

Phenomenon, 5 f.

Philosophy, natural, 4
of nature, 4, 7, 9
of the organism, 9, 15

Phylogeny, 255, 291, 297, 304 ff.

Physiology, 12
of development (morphogenesis), 20

*Planaria*, 130, 155, 162 f., 200

Plants, 48 f.

Plato, 2

Pluteus, 42

Poisons, 205 ff.

Pole, 36

Polarity, 106

Potencies, complex, 112, 120
explicit, 84
implicit, 84
primary, 84, 111
prospective, 77 ff., 83, 89, 118, 125, 241
secondary, 84, 110

Poulton, 198

Precipitin, 207 f.

Pressure experiments, 63, 141

Primary potency, 84, 111
purposefulness, 146, 287
regulation, 85, 174, 188

Progress, 305

Pronuclei, 55

Prospective potency, 77 ff., 83, 89, 118, 125, 241
value, 77 f., 80, 122

Protista (Protozoa), 27, 130, 236

Protoplasm, 28, 30
morphogenetic rôle of, 67

Przibram, 112, 248

Rádl, 247

Rauber, 235

Reaction, answering, 181

Reciprocity of harmony, 156 f.

Re-differentiation, 75, 111, 163

Regeneration, 55, 74, 105, 111, 221
super-, 115 f.

Regulation, 68, 73, 85, 111, 165
defined, 166
metabolic, 198 f.
secondary, 85, 165, 188

Reinke, 146

Restitution, 21, 74, 110, 112 ff.
defined, 166
and Darwinism, 267
and Lamarckism, 286
of second order, 158

Retina, 191

Retro-differentiation, 163 f.

Rhumbler, 93

Ribbert, 114

Rickert, 315 ff.

Roux, 26, 48, 55 ff., 66 f., 76, 89, 92 f., 108, 161, 176 f., 241

Rubner, 193

Sachs, 117

Sadebeck, 279

*Salamandra*, 175, 281

Schneider, 146

Schultz, E., 200

Schultze, O., 67

Schwendener, 177

Science, 14, 297
natural, 1 ff.
rational, 12

Sea-urchin, *see* Echinus

Secondary potency, 84, 110
regulation, 85, 165, 188

Secretion, internal, 116, 200

Segmentation, 35

Selective qualities (of tissues), 186

Self-differentiation, 108

Semon, 216 f.

Sex, 107

Single, the, 315 ff.

Skeleton, 40 ff., 44, 47, 92

Spemann, 105

Spermatozoon (spermia), 32 ff.

Splitting (of hybrids), 229 f.

Stahl, 197

Standfuss, 278

Starfish, 44, 81, 122

Starling, E., 116, 204, 212

*Stentor*, 131

Stimuli, directive, 102 ff.
formative, 102 ff., 113, 118, 133
of restitutions, 113 f.

Structure of protoplasm, 66, 69, 72 f. 85, 88

Substance, living, 17

Sumner, 196

Super-regeneration, 115 f.

Surface-tension, 91

Sutton, 230

Symmetry, 39, 68, 70, 72, 89, 98

System, combined types of, 153 ff.
complex, 219 f.
complex-harmonious, 155
equipotential, 120
harmonious-equipotential, 121 ff., 151 f.
mixed-equipotential, 154
morphogenetic, 119 f., 163, 241

Systematics, 14 ff., 21, 243 f., 253, 264, 293, 296

Taine, 308, 310

Theology, natural, 1 ff.

Thomson, J. A., 16

Thymus, 204

Thyroid, 204

Tissue, 38

Toxins, 207 f.

Transformism, 251

Truth, 7

Tschermak, 228

*Tubularia*, 126 ff., 133, 158 ff.

Type, 48, 247 f., 282, 291

“Understanding” (historically), 302

Universality, postulate of, 148 f.

Universe, 5

Univocality, principle of, 161

“Values,” 317 ff.
prospective, 77 f., 80, 122

Variation, 218, 237 f., 276

Variation, fluctuating, contingent, 264 f., 273 f., 282, 290

Vernon, 232, 238

Vitalism, 143, 145 f., 210 f., 224 f., 234, 240 f., 272, 277

Vöchting, 174, 179 f., 182, 221

Volition, acts of, 274

Vries, de, 228, 238 f.

Wallace, 292

Ward, J., 8, 143

Weber, law of, 191

Weinland, 202

Weismann, 33, 52 ff., 58 f., 72, 74 f., 103,
111, 138, 214 f., 237, 277 f.

Weldon, 238

Whole, the, 28, 80, 117
-embryo, 61, 67 f.

Wigand, 255, 266, 292

Wilson, E. B., 27, 65, 70 f., 86 f., 107

Windelband, 13 f.

Winkler, 116, 221

Winterstein, 199

Wolff, C. F., 26

Wolff, G., 105, 146, 255, 266, 287 f.

Wolff, J., 177

Yung, 177

Zeleny, 112, 115, 212

Zur Strassen, 93

THE END

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