Chapter X: Part I: The Individual Organism with Regard to Form and Metabolism (7)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

THE SIGNIFICANCE OF THE MATERIAL CONTINUITY IN INHERITANCE

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

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

THE EXPERIMENTAL FACTS ABOUT INHERITANCE

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

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

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

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

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

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

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

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

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

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

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

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

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

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

THE RÔLE OF THE NUCLEUS IN INHERITANCE

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

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

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

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

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

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

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

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

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

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

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

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

VARIATION AND MUTATION

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

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

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

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

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

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

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

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

CONCLUSIONS FROM THE FIRST MAIN PART OF THESE LECTURES

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

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

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

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

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