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.