In the preceding chapters certain matters had to be taken for granted, since it was not possible, or desirable, at the time to discuss more fully some of the terms that are in common use, or to analyze more completely many of the phenomena. It was also not necessary to give the general point of view under which the phenomena were considered in their physical, chemical, or even causal connection. Little harm has, I trust, been done by relegating such questions to the final chapter. An attempt will now be made to give more explicit statements in regard to the use and meaning of such terms as “organization,” “polarity,” “factors,” “formative forces,” “vitalistic” and “mechanical principles,” “adaptation,” etc.

It will be found that the hypotheses that have been advanced to account for the phenomena of development and of regeneration may be roughly classified under two heads: first, those in which the organization is “explained” as the result of the collective action of smaller units; and second, those in which the organization is itself regarded as a single unit that controls the parts. Let us examine these points of view more in detail, in order to see what has been meant in each case by “the organization.”

A favorite method of biological speculation in the last forty years has been to refer the properties of the organism to invisible units, and to explain the action of the organism as the resultant of their behavior. The hypothesis of atoms and of molecules, by means of which the chemist accounts for his reactions, has proved so exceedingly fruitful as a working hypothesis that it has had, I think, a profound influence on the mind of many biologists, who have, consciously or unconsciously, attempted to apply a similar conception to the structure of living organisms. The discovery that all of the higher organisms are made up of smaller units, the cells, and that the lower organisms are single, isolated cells, comparable to those that make up the higher forms, has also drawn attention to the idea that the whole organism is the result of the action of its units. Furthermore, within the cells themselves units of a lower order have also been discovered, such, for instance, as the chromosomes, the chlorophyl bodies, etc., that repeat on a smaller scale some of the fundamental properties of the entire organism, as growth and division. It has been assumed that still farther down in the structure there are smaller units having the same properties, and the smallest of these are the ultimate units. The organism is looked upon as the result of the properties of these minute germs. The gemmules of Darwin furnish an example of an hypothesis of this sort; also the intracellular pangens of De Vries, the plasomes of Wiesner, the biophors of Weismann, the idiosomes of Hertwig, and the micellÆ of NÄgeli are other examples of this way of interpreting the organization. These elements are endowed by their inventors with certain properties, and these are of such a sort that they give the appearance of an explanation to organic phenomena. It is useless to object to these hypotheses that they are purely ideal, or fictitious, and that those properties have been assigned to the germs that will bring about the desired explanation, and have not been shown to be the real properties of the germs themselves. But apart from the arbitrariness of the process, it cannot be claimed that a single one of these creations has been shown to be true, or has even been accepted by zoologists as probable. A more serious objection to this point of view is that the most fundamental characteristics of the organism, those that concern growth, development, regeneration, etc., seem to involve in many cases the organism as a whole. So many examples of this have been given in the preceding pages, that it is not necessary to go over the ground again. It has been shown that a change in one part takes place in relation to all other parts, and it is this interconnection of the parts that is one of the chief peculiarities of the organism. In phenomena of this kind even the cells seem to play a secondary part, and if so, we can, I think, safely leave out of account the smaller units of which the protoplasm is supposed to be built up and we can neglect them, if for no other reason than this, that the argument that has called them into existence starts out with the cell as the highest unit. If the cell can be thrown out, most probably the units of which the cell itself is supposed to be made up can be safely disregarded also.

It may be objected that only through a knowledge of the minute structure of the organism can we hope to understand the behavior of the whole; but my point of view is not that there may not be a fundamental structure, but that this is not formed by a repetition of elements, which give to the whole its fundamental properties. It can be shown, I think, with some probability that the forming organism is of such a kind that we can better understand its action when we consider it as a whole and not simply as the sum of a vast number of smaller elements. To draw again a rough parallel; just as the properties of sugar are peculiar to the molecule and cannot be accounted for as the sum total of the properties of the atoms of carbon, hydrogen, and oxygen of which the molecule is made up, so the properties of the organism are connected with its whole organization and are not simply those of its individual cells, or lower units.

The strongest evidence in favor of this view is found in the behavior of small pieces of an egg, or of a protozoon, or even of a many-celled organism. A lower limit of organization is very soon reached, below which the piece fails to produce the characteristic form, although all the necessary elements are present in the piece to produce the entire structure. The size of these pieces is enormously large as compared with the size of the cell, or of the imaginary elements of NÄgeli, Weismann, Wiesner, etc. These results indicate that the organization is a comparatively large structure.

A few writers have either ignored the presence of smaller units, or have dealt with the organism from a purely chemical and physical point of view. They attempt to account for the changes in the organism as the outcome of known physical and chemical principles. It must, of course, be granted that in a sense the properties of the organism are the result of the material basis of the organism; but in another sense this idea gives a false conception of the phenomena of life, because, if we were simply to bring together those substances that we suppose to be present in the organism we have no reason to think that they would form an organism, or show the characteristic reactions of living things. Even from a chemical point of view we can see how this result could not be expected, for it is well known that the order in which a compound is built up, i.e. the way in which the atoms or molecules are introduced into the structure, is an important factor in the making of the compound. When we remember the immense period of time during which the organisms living at present have been forming, we can appreciate how futile it will be to attempt to explain the behavior of the organism from the little we know in regard to its chemical composition. Its chief properties are the result of its peculiar structure, or the way in which its elements are grouped. This structure has resulted from the vast number of influences to which the organism has been subjected, and while it may be granted that if we could artificially reproduce these conditions an organism having all the properties that we associate with living things would result, yet the problem appears to be so vastly complicated that few workers would have the courage to attempt to accomplish the feat of making artificially such a structure. To prevent misunderstanding, it may be added that while from the point of view here taken, we cannot hope to explain the behavior of the organism as the resultant of the substances that we obtain from it by chemical analysis (because the organism is not simply a mixture of these substances), yet we have no reason to suppose that the organism is anything more than the expression of its physical and chemical structure. The vital phenomena are different from the non-vital phenomena only in so far as the structure of the organism is different from the structure of any other group of substances.

NÄgeli has stated that each part acts as though it knew what the other parts are doing. His idea of the idioplasm involves a conception of the organism as a whole and not simply the sum total of a number of parts. Hertwig, who maintained at one time that the development of the embryo is the resultant of the action of the cells on each other, admits in his work on Die Zelle und die Gewebe that while this is in part true, yet on the other hand the whole also exerts an influence on its parts. Driesch, who hypothetically suggested at one time that the nuclei act as centres of control of the cell by means of enzymes, has later adopted a widely different view. Whitman has made a strong argument to the effect that the cell theory is too narrow a standpoint from which to treat the organism, and on several occasions I have urged that the organism is not the sum total of the action and interaction of its cells, but has a structure of its own independent of that of the cells.

This discussion will suffice to show some of the opinions that have been held as to the nature of the organization of the organism. Let us next ask what properties we may ascribe to it.

It has been found that certain polar, or rather dimensional, relations are characteristic of the organization. The term “polarity” expresses this in a limited way, but refers only to one line having two directions, while we now know that the dimensional properties relate to the three dimensions of space, and for this idea we might make use of the term heterotropy. Thus we find that a piece of a bilateral animal regenerates a new anterior end from the part that lay nearer the anterior end of the original animal, a new right side from the part that was nearest the original right side, and a new dorsal part from the region that lay near the original dorsal part, etc.

The polarity of a part can be changed in certain forms, as in tubularia, by exposing the posterior cut-end to the external factors that bring about the formation of a hydranth, or, as in hydra, by grafting in a reversed direction a smaller piece on a larger one. In Planaria lugubris and in the earthworm the polarity of the new tissue may be reversed, as compared with that of the part from which it develops, if the new part arises from certain regions of the body. A curious instance of the effect of the polarity is shown by the regeneration from an oblique surface in planarians. The new head arises from the more anterior part of the new material, rather than from the middle of the anterior oblique surface, and the new tail arises from the more posterior part of the posterior oblique surface. As an analysis of this result has been already attempted in an earlier chapter, it will not be necessary to go further into this question here.

The development of a new part at right angles to an oblique surface has also been described, and it has been pointed out that the result appears to be due to the symmetrical development of the new structure in the new part. This symmetry of the newly forming part must be also counted as one of the properties of the organization.

Finally, the mode of regeneration of a new, bifurcated tail in the teleost, stenopus, shows that the new part may very early become moulded into the characteristic form, and that the growth of the different parts is regulated by the structure assumed at an early stage. The new part does not grow out at an equal rate until it reaches the level of the notch of the old tail, and then continue to grow at two points to produce the bilobed form of the tail; but the bilobed condition appears at the very beginning of the development.

These illustrations give us nearly all the data that we possess at present on which to build up a conception of the organization. That we must fail in large part fully to grasp its meaning from these meagre facts is self-evident. The main difficulty seems to lie in this,—that when we attempt to think out what the organization is we almost unavoidably think of it as a structure having the properties of a machine, and working in the way in which we are accustomed to think of machines as working. The most careful analysis of the “machine theory,” as applied to the phenomena of development and of regeneration, has been made by Driesch. It has been pointed out that in his Analytische Theorie Driesch assumed that development is due to “given” properties in the egg; that each stage is initiated by some substance contained in the egg acting on the stage that has just been completed. That is, each stage is the condition of the following. The “rhythm” of development is accounted for in this way. The changes are described as due to chemical processes (including also ferment actions). The nucleus is supposed to contain all the different kinds of ferments that act, when set free, as stimuli on the protoplasm; but since the ferments are always set free at the propitious moment, Driesch was obliged to assume that the cytoplasm acts on the nucleus in such a way as to make it produce the proper ferment for the next stage. Thus the cytoplasm first influences the nucleus, the latter sets free a specific ferment that starts a new chemical change in the cytoplasm, and the changed cytoplasm may then react again on the nucleus, and a different ferment be set free, etc. Each change is therefore not only an effect of what has gone before, but the cause of the next process.[132] Driesch points out that it is necessary at this stage to make a further assumption, because the cytoplasm must not only be acted upon by the ferment, but it must itself be of such a sort that it responds to the action. This leads to a great complication of the phenomena; but the assumption does not depart, in the last analysis, from the idea of the cell as a system in a mechanical sense. This assumption of a receiving and an answering station for the stimuli carries with it the further assumption of a many-sided “harmony.” Without a harmony at each step in the development there could be no orderly ontogeny. The assumption of this harmony introduces a new element into the series of hypotheses. The appearance of a causal explanation was given in those parts of the argument preceding the introduction of the assumption of a harmony, but with the admission of this new element into the argument, the causal point of view is left. Driesch says in this connection: “If we cannot gain a singleness of view in the way that has been followed, we can reach this in another way. Indeed, the way of doing so has been already implied in that part of the theory dealing with the harmony of the phenomena. The existence of this harmony is inferred, because, in the large majority of cases, the ontogeny leads to a typical result. Therefore we must assume that the conditions for the end result are given—the conditions are the harmony itself.” Put somewhat less obscurely, if more crudely, we may express Driesch’s idea by saying that the harmony that stands for a hen is given in the hen’s egg.

Driesch adds: “Because a typical result always follows, therefore every single step in the ontogeny must be judged, from an analytical standpoint, from the point of view of the result itself. The result is the purpose of the ontogeny. It is as though we visited daily a wharf where a ship is being built,—everything appears a chaos of single pieces, and we can only understand what we see when we consider what is to be made. Only from a teleological point of view can we speak of a development, for this term expresses the very existence of an object to be developed. The term is used fraudulently if it is intended to mean that the development is the outcome of ‘processes,’ using this term in the sense that a mountain or a delta develops from physical processes.” “We can only reach a satisfactory view of the phenomena when we introduce the word ‘purpose.’ This means that we must look upon the ontogeny as a process carried out in its order and quality as though guided by an intelligence. We arrive at this conclusion, because the individual whole is ‘given,’ as the clearly recognized goal of the entire process of development.”

In a later attempt to analyze the problem of development, Driesch examined it more fully from the point of view of the machine theory. This contribution must be looked upon rather as a tour de force that is intended to show how far this idea can be carried in its application to development. Driesch explains that in his analytical theory he assumed from what is “given” in the egg that the egg can be understood causally, as a machine is understood, but what is “given” can be understood only teleologically. He says: “What I defended was not vitalism, but, so far as the phenomena of life are concerned, exactly the current physico-chemical dogmatism; but I did not fail to see and to point out the consequences of this dogmatism, which every one (except Lotze) has avoided, viz., that the adaptive basis in which the living phenomena take place is ‘given.’” Driesch defines his view as formal-teleological, in contrast to vitalistic. The former may also be called a machine theory of life in which the purpose is given, not explained.

In later writings Driesch has thrown over some of his earlier conclusions and adopted a causal-vitalistic philosophy. The basis of this new conception is found in the proportional development of parts of an original whole, as has been explained in a preceding chapter. This result belongs to a category of phenomena that is in principle not machine-like, but of a specifically different kind. It is something that cannot be explained by the agencies of the outer world, such as light, gravity, salinity, temperature, etc. After examining other hypotheses, Driesch returns to a view that he had previously rejected, viz. the conception of “position,” by which is meant the influence of the location in the whole. This position has certain directions, but nothing in addition that is typical. By the term “location in the whole” is meant that the word “location” (Lage) shall refer not to geometric space, but to the organization of the object that has its own directions. A deformation of the whole may change very little the relative location of the parts.

In his earlier writings Driesch rejected this idea, because it did not seem to satisfy our etiological need, and also because he thought that he could reach his goal from the standpoint of initiating stimuli (AuslÖsungen). Driesch now assumes that the stem of tubularia and the archenteron of the starfish, for example, have a polar structure. Bilateral forms, as the whole larva of the starfish, have a coÖrdinated system of two axes with unlike poles and one axis with like poles, each of a given length or proportion. The ends of the axes are characteristic points of the system. If, in such a system, a typical act of differentiation appears, to which we can assign a cause, so far as the location is concerned, a change will occur as follows: To take the simplest case, that of a system with only one axis having unlike poles, as the archenteron of the starfish, in which differentiation has not begun, we can picture to ourselves the formation of the divisions of the archenteron in a causal way by supposing the end of the axis, or pole, to be the location (Sitz) of an initiative “action at a distance” (auslÖsende Fernkraft). This locality, just because it is the end of a system, is something special; and it acts in such a way that wherever an effect is produced, it is the cause of that effect. This very way of looking at the problem postulates a sort of causal harmony. But how, it may be asked, can a special point or pole of an axis bring about an action in the system? This can be shown by means of a simple case, viz. the dividing up of the archenteron of the starfish into its characteristic parts. There are two effects produced, viz. the formation of the two constrictions of the wall. We need not consider the fact that the constrictions are formed, for this is established in the potence of the system, and is awakened by the initiating cause, but the place at which the constrictions are produced is that for which we should account. We must think of this cause as “action at a distance,” and indeed as an “action at a distance” that works at a determinate, typical distance. This inherent measure of distance of the action is not one of absolutely fixed size, for a gastrula made shorter by an operation also subdivides into proportionate parts. The action starts from the poles of the system, and acts, not at an absolute, but at a relative distance, since it is dependent upon the length of the axis of the whole differentiating system. “The localization of ontogenetic processes is a problem sui generis. The phenomenon can always be expressed on the scheme of cause and effect, if we assume the ‘action at a distance’ to start from fixed points of a differentiating system.”

In regard to the criterion of vitalistic phenomena Driesch makes the following statement: “On the current view we are inclined to see, in the formative changes, actual causes at work that even initiate those processes that we call stimuli; we do so because we pretend at present to know something of the special mechanism by which the formative changes work. The effects come into play through a causal union of simple processes of a physical-chemical sort that we may call a chain of stimuli. From the new point of view, the initiatory stimulus is not an initiatory cause or the effect of a causally united chemico-physical phenomenon. The stimulus is, from this point of view, a true stimulus, but the effect is not a true effect of its initiation, but is rather to be designated a responsive effect, for there is no connecting chain of stimuli. It is in the place of the latter that the vitalistic view appears. The only data of a machine sort in the conception are the arrangements for the reception and guidance of the stimulus, perhaps also the means for carrying out the response effect; for the machine data are only the prerequisites of the phenomena, but in themselves do not bring about the result.”

Driesch finds in this argument a demonstration of the vitalistic doctrine, but vitalism, of course, of a very special kind. Without a more elaborate presentation of his view it is not possible to give a detailed criticism of his conclusions; but a few of the more obvious objections that may be brought against this view may be discussed. The assumption of “action at a distance” does not, I think, in any way help to make the phenomenon clearer. The formation of a typical larva of normal proportions from a piece of an egg is just as mysterious after the assumption of an “action at a distance” of a proportionate sort as it was before. Driesch has introduced into the argument to establish a vitalistic standpoint one of the most obscure ideas of physical science. There is, so far as I can see, no necessity for such an assumption, since there is present in every case a continuous medium of protoplasm, which would seem to make this idea at least superfluous. Moreover, the additional element that Driesch has added to his conception of the process, namely, an action in proportion to the size of the piece, is objectionable if for no other reason than that it attributes to the unknown principle of “action at a distance” a quality that is the very thing that ought itself to be explained. This assumption, it seems to me, begs the entire question, and we can give no better explanation why it should belong to the principle of “action at a distance” than to anything else. Far from having given a demonstration of vitalism, Driesch has, I think, in his analysis simply set up an entirely imaginary principle, which, taken in connection with other undemonstrable qualities, is called vitalism.

If we cannot accept Driesch’s demonstration of vitalism, from what point of view can we deal with the phenomenon of the production of a typical form from each kind of living material? Can we find a physico-chemical explanation of the phenomenon? Enough has been said to show that this property is one of the fundamental characteristics of living things and is, in all probability, a phenomenon which we certainly cannot at present hope to explain. Yet the question raised by Driesch is, at bottom, not so much whether we can give a physico-chemical explanation, but whether the phenomenon belongs to an entirely different class of phenomena from that considered by the physicist and by the chemist. Let us examine the results and see if we are really forced to conclude that there is no other physico-causal point of view possible.

In many cases in which a response to an external stimulus takes place, we must assume a physico-causal connection between the stimulus and the effect. The action of poisons, for instance, is an example of this kind, and, in some cases, as in the formation of the galls of plants, the stimulus of a foreign body may lead to the development of a structure, the gall, of a definite form. The experiments of Herbst on the effect of lithium salts in sea water on the development of the sea-urchin embryo lead to a similar conclusion. The changes in form that result from other external agents, such as light, gravity, contact, etc., can be best understood from a physico-causal point of view, and it seems improbable at least that their action within the organ is transformed into a vitalistic causal action through Driesch’s principle of an “action at a distance.”[133] The effect of internal factors on the change of form is, however, much more difficult to deal with, since we know so little at present about these factors. Here we find amongst other phenomena that of the proportionate formation of a whole organ from a part of an old one, or of an egg. We find it difficult, if not impossible, to attribute this directly to external causes, yet, as I have tried to show, the first steps through which this takes place can be referred to physico-causal principles. These are the separation of the piece from the whole; the change of the unsymmetrical piece into a symmetrical one, brought about, in part at least, by contractile phenomena in the piece, aided, no doubt, in some cases by surface tension, etc. These changes give the basis for the development of a new organization along the lines of structure that are already present in the piece. We find here the beginning of a physico-causal change, and, so far as I can see, we have no reason to suppose that at one stage in the process this passes over into the vitalistic-causal principle. It should, I think, be pointed out in this connection that even in the physical sciences it would not be difficult to establish a vitalistic principle, or whatever else it might be called, if we chose to take into account such properties of bodies as those which the chemist calls the affinities of atoms and molecules, or the symmetrical deposition of material on the surface of a crystal from a supersaturated solution, etc. These phenomena are usually looked upon as “given,” that is, beyond the hope of possible examination. Until these questions are more fully understood scientists are, I think, justified in showing a certain amount of self-restraint in regard to the solution of such problems. Du Bois-Reymond has summed up this point of view in the dictum, “Ignorabimus,” which is interpreted to mean, not only that we are ignorant at present on certain questions, but that we know we must remain ignorant. The formative changes in the organism appear to belong to this category of questions. This confession of ignorance need not mean that we cannot hope to discover the conditions under which the phenomena take place, so that we can predict with certainty what the results will be, but the meaning of the change itself may remain forever obscure, at least from our present conception of physico-chemical principles. Shall we, therefore, call ourselves vitalists, because we find certain phenomena that we cannot hope to explain as the result of physical principles, or for which we must invent an unknown principle? Or can we succeed in demonstrating a different kind of principle in living things? If we could, we might be justified in calling ourselves by the name of vitalists. But who has made such a discovery? Does the well-known phenomenon of proportionate development give a demonstration of the unknown principle? Would one be justified in claiming a different principle that is not a physico-causal one, because the nerve impulse is different from any known physical phenomenon? The preceding pages have made clear, I hope, that, for my own part, I see no grounds for accepting a vitalistic principle that is not a physico-causal one, but perhaps a different one from any known at present to the physicist or chemist.

In order to make clear in what way certain terms have been used in the preceding chapters, it may not be out of place to indicate how it is intended that they should be employed. The word “cause” has been used in the sense in which the physicist uses the term. A “stimulus” is the chain of effects of a cause acting on a living body. In certain cases the cause itself may be spoken of as the stimulus, but only when its specific action on a living body is implied. A “factor” is a more general term and is usually one or more of a number of causes that produce a result. It may prove convenient to use this term where a change in form is produced. Thus the size of a piece is one of the factors that determines the result; the part of the body from which the piece is taken may also be a factor, or rather the kind of material contained in the piece. These examples will suffice to show that the word is used for an observed connection of a very general sort, especially for those cases in which we have not analyzed the factor into its components. The term is especially useful for cases in which the change in form is the outcome of the innate properties of the organization. The term may be used so that it need not prejudice the result, either in favor of a physico-causal or a vitalistic-causal point of view. It may be convenient to use it as an indifferent term in these respects. The word “force” I have attempted to avoid as far as possible, except in such current expressions as “the force of gravity,” etc., for, apart from the loose way in which the word is used even by physicists, we know so little about the forces in the organism that it is best, I think, to use the word as sparingly as possible, and only where a known physical force can be shown to produce an effect.

Much misunderstanding has arisen in connection with the term “formative force.” In the first place we naturally associate with this term the meanings attached to it by writers of the seventeenth and eighteenth centuries. They assumed a formative principle in living things, that is an expression of a formative force. Roux, who has more recently used the term, has attempted to avoid misunderstanding by using the plural,—“the formative forces of the organism”; but even under these circumstances, differences of opinion have arisen, as shown by the controversy between Roux (’97) and Hertwig (’94 and ’97), on this point. A change in form carries with it a change of position of the parts, and the latter involves the idea of forces, but the nature of these forces is entirely obscure to us, at least we cannot refer them to any better-known category of physical or chemical forces. They may, perhaps, be most profitably compared to the forces of chemical union, but whether they are very numerous or can be reduced to a limited number of kinds of force, we do not know. If it could be shown that the changes in the organism are due to molecular changes, then the formative forces might appear to be only molecular forces, but we are not in position at present to demonstrate that this is the case, however probable it may appear.

Finally, the use of the term “organization” may be considered, although from what has been said already it is clear that there must be a certain amount of vagueness connected with our idea of what the organization can be. The organization, from the point of view that I have adopted, is a structure, or arrangement of the material basis of the organism, and to it are to be referred all the fundamental changes in form, and perhaps of function as well. We also use the term as applied to the completed structure, by which we mean that the organism consists of typical parts having a characteristic arrangement carrying out definite functions. When applied to the egg, or to a regenerating piece, the term refers to some more subtle structure that we are led to suppose to be present from the mode of behavior of the substance. As pointed out, we know this organization at present from only a few attributes that we ascribe to it, and are not in a position even to picture to ourselves the arrangement that we suppose to exist.

REGENERATION AND ADAPTATION

One of the most difficult questions with which the biologist has to deal is the meaning of the adaptation of organisms to their environment. PflÜger, in an article entitled “The Teleological Mechanics of Living Nature,” has drawn attention to the teleological character, or purposefulness, of certain processes in the living organism. “There has been found only one general point of view, which if not absolute, yet is the rule, to account for the eternal transformations of energy in the living body. Only those combinations of causes take place that are as favorable as possible for the welfare of the animal. This holds true even when entirely new conditions are artificially introduced into the living organism. What is more remarkable than that, even in the highly organized mammal, there should be a regeneration of the bile duct after its removal, or that after a large piece of a nerve has been extirpated by a severe operation it should be again renewed?... What is more surprising than that the organism should become accustomed to the most diverse kinds of organic and inorganic poisons?... And, finally, there are a number of facts that make good the law that changes appear to be governed by no other principle than the purpose of making certain the existence of the organism.”

PflÜger’s teleological law of causality is that “the cause of every need of a living being is at the same time the cause of the fulfilment of the need.” PflÜger explains that the word “cause” is here intentionally chosen in order to bring out the necessary, lawful connection in which the cause of each need stands in relation to the fulfilment of that need. He adds that it would have been more correct, but less pointed, to have said “motive” or “inducement” instead of “cause.”

In order to illustrate what is meant by this law, the following examples may be given. Food and water bring back the organism to its normal condition. The absence of food in the body leads to hunger, and this to the taking in of more food; or, in other words, the need of food leads to the search for food, or at least to the taking in of food. The sexual desire, or the need to reproduce, brings about the condition of the animal that leads to reproduction. A defect in the valves of the heart leads to the enlargement of the right or the left ventricle. The removal of one kidney leads to the hypertrophy and increased function of the other. And although not explicitly stated by PflÜger in this place, we may add to this list the removal of a part of an animal, that leads to the regeneration of that part. PflÜger further states that we are making no subtle distinction when we point out that these phenomena, if looked at from the point of view of purposeful acts, appear to have a teleological side. In reply to this it may be stated, however, that in certain cases of regeneration it can be shown that the result is entirely useless, or even injurious to the organism; hence the teleological nature of the process is entirely lost sight of, and we are the more ready to accept a simple causal explanation of the phenomena. The best example of this that I can give is the development of a tail at the anterior end of a posterior piece of an earthworm. This process is not an occasional one, but is constant. An example of an apparently useful result, so far as the individual’s well-being is concerned, but entirely useless from the point of view of the continuance of the species, is found in the development, in the earthworm, of a new head after the removal of the anterior end, including the reproductive region. New reproductive organs are not formed, and, although, in virtue of the regeneration of a new head, the individual is capable of carrying on its existence, yet the race of earthworms is not thereby benefited. The production of two tails in lizards, or of two or more lenses in the eyes of newts, are examples of the regeneration of superfluous structures.

If, however, it is claimed that in the large majority of cases the process of regeneration is for the welfare of the individual, and for the race also, this must be admitted, and it is this fact which has made a deep impression on the minds of many biologists.

From the causal point of view, we may look upon the formative changes as the necessary outcome of strictly causal principles, and we may suppose that they take place without respect to the final result. But the question before us is rather to explain, if possible, why the changes that take place are in so many cases useful ones. That they are not always useful must be admitted, that they sometimes are must be granted, and it is the latter alternative that has attracted special attention. Now it is undoubtedly the simplest solution to claim that the scientist has nothing to do with the adaptiveness of the response, that his whole problem lies in a study of the causal phenomena involved in each process, but it is unquestionably true that scientists have not been satisfied to confine their hypotheses to this side of the question. The widespread interest in the theory of natural selection is, I think, due to the fact that it appears to offer an explanation of the formation of adaptive processes—not that it pretends to explain the origin of the adaptive structures or processes themselves, but that it seems to account for the adaptiveness of the fully formed product, i.e. the organism. For it will be seen that if only those forms (variations) survive that are useful, and survive either because the environment selects them (and exterminates the others), or because new forms that arise find a new place in nature where they can remain in existence, then the adaptiveness of the form to its surroundings would seem to be accounted for. In this case we can see how the causal processes that take place in the organism need have no causal connection with the environment,—except in the sense that the environment has acted as a selective agent, and appears, therefore, in the light of a teleological factor. But, as has been said before, the question is not so much that organisms are adapted, as that organisms respond adaptively to changes to which they can never have been subjected before. It is for the latter fact that a solution is to be sought.

In this whole question there is danger of extending our own experience as agents in the constructing of products useful to ourselves, to the organic world, in attempting to account for the way in which the useful characters of organisms have arisen. We see a ship being built, and we know that when it is finished it will be useful. We explain its building by its future usefulness,—that is, we explain the process as the result of human teleology. But have we any right to extend this principle to the organic world, and infer that processes are there carried out because they will ultimately be useful to the individual in which they take place? Unconsciously we have shifted our point of view. The ship does not build itself, and the final result of the building is of no use to the ship. On the contrary, the organism does build itself and the result is useful only to itself. Unless we suppose that some external agent acting as we do ourselves directs the formative processes in animals and plants, we are not justified in extending our experience as directive agents to the construction of the organic world; and if we are not justified in drawing such a conclusion, since the organism by no means always responds adaptively, and in many cases very badly and incompletely, then, it seems to me, we must look for another point of view.

In connection with his work on the regeneration of the eye of the salamander, Gustav Wolff (’93) has made some sweeping statements in regard to the phenomenon of adaptation. “Purposeful adaptation is that which makes the organism an organism. It is this adaptation that appears to us as the most characteristic property of all living things. We can think of no organism without this characteristic.” In another place he states, “...we recognize that every explanation that presupposes the living being, every post-vital explanation of organic adaptation, presupposes in every case that which it attempts to explain; we recognize that the explanation of adaptation must coincide with the explanation of life itself.” There is, perhaps, some truth in this statement, but, on the other hand, Wolff has, I think, shot somewhat over the mark. As Fischel (1900) has pointed out, the response is sometimes not adaptive, as when two lenses develop in the same eye in the salamander; and, we may add, as when an antenna develops in certain crustacea in place of an eye, or as when a tail develops instead of a head, or a head in place of a tail. In the light of these facts, it is, I think, going too far to assert that the power of living things to respond adaptively to changes in themselves or in their environment is synonymous with life itself. All that we can fairly claim is that in several cases living forms have been shown to be able to complete themselves, and this may be interpreted as an adaptive response. It would carry us far beyond the scope of the present volume to discuss the question of adaptation in general, and I think it highly probable that it will prove true that there are many kinds of adaptive responses that must be considered separately and each on its own merits. Let us, therefore, confine our concluding remarks entirely to regenerative changes which, after they have been completed, are for the good of the organisms. Our preceding discussion has led to the conclusion that the phenomena of regeneration are not processes that have been built up by the accumulation of small advances in a useful direction; that they cannot be accounted for by the survival of those forms in which the changes take place better than in their fellows, for it is often not a question of life and death whether or not the process takes place, or even a question of leaving more descendants. On the contrary, it seems highly probable that the regenerative process is one of the fundamental attributes of living things, and that we can find no explanation of it as the outcome of the selective agency of the environment. The phenomena of regeneration appear to belong to the general category of growth-phenomena, and as such are characteristic of organisms. Neither regeneration nor growth can be explained, so far as I can see, as the result of the usefulness of these attributes to the bodies with which they are indissolubly associated. The fact that the process of regeneration is useful to the organism cannot be made to account for its existence in the organism.