In the male, the mass of spermatozoa does not swell out the body to such an extent that its walls must give way and thus permit an exit, but the large ectoderm cells atrophy spontaneously at the time of maturity, and as they fall off, exit is given to the spermatozoa here and there. In this instance also the dissolution of the body is not a consequence of reproduction, but reproduction can only take place when the dissolution of the body has preceded it!
In this remarkable arrangement we cannot discern anything except an evident adaptation of the life of the body-cells to reproductive purposes, and this adaptation was rendered possible because, after the evacuation of the sexual cells, the body ceased to be of any value for the maintenance of the species.
But even if we assume, that the death of the Orthonectides is, in Götte’s sense, a consequence of reproduction, inasmuch as, in the two forms of females as well as in the male, the extrusion of a mass of developed germ-cells or embryos deprives the organism of the physiological possibility of living longer, how can we explain the necessity of death as a direct consequence of reproduction in all Polyplastides? Is the body—the soma—of the Metazoa so imperfectly developed, as compared with the reproductive cells, that the extrusion of the latter involves the death of the former? As a matter of fact in the majority of cases the relations are reversed; the number of body-cells usually exceeds the germ-cells a hundred- or a thousand-fold, and the body is, as regards nutrition, so completely independent of the reproductive cells, that it need not be in the least disadvantageously affected by their extrusion. And if the Orthonectid-like ancestors of the Metazoa were compelled to give up their insignificant somatic part after the extrusion of their germ-cells, because it could now no longer support itself, does it therefore follow that the somatic cells had for ever lost the power of surviving, even when their phyletic descendants were surrounded by more favourable conditions? Had they to inherit ‘the necessity of death’ for all time? Whence came this great change in the nature of organisms which, before the differentiation of Homoplastids into Heteroplastids, were endowed with the immortality of unicellular beings?
And it must be remembered that it is only an assumption which places the Orthonectides among the lowest Metazoa (Heteroplastids). I do not intend to greatly emphasize this point, but the formation of the Gastrula by embole, and the absence of a mouth and alimentary canal, shows that these parasites are extremely degenerate, and the same may be said of almost all endoparasites. The Gastrula, as an independent organism, was without doubt primitively provided with both mouth and stomach, and the mass of ova filling the female Orthonectid is an adaptation to a parasitic life, which on the one side renders the possession of a stomach a superfluity, and on the other demands the production of a great number of germ-cells[[78]]. It is certain that the Orthonectides, as at present constituted, cannot have lived in the free condition, and also that their adaptation to parasitism cannot have arisen at the beginning of the phyletic development of Metazoa, because they inhabit star-fishes and Nemertines—both relatively highly developed Metazoa. Hence it is, at any rate, doubtful whether the Orthonectides can claim to pass as typical forms of the lowest Heteroplastids, and whether their reproduction can be looked upon ‘as typical for the unknown ancestors of all Polyplastids’ (l. c., p. 45). If, however, we accept some organism resembling these Orthonectides as the most ancient Heteroplastid, being a free-living organism, it must have had a stomach, and the cells surrounding it must—as a whole or in part—have possessed the power of digesting; at any rate, they cannot all have been germ-cells, and therefore it is improbable that death would be the direct result of the extrusion of the germ-cells.
Let us now consider the manner in which Götte has endeavoured to explain the transmission of the cause of death—which first appeared in the Orthonectides—from these organisms to all later Metazoa, until the very highest forms are reached. Exact proofs of this supposition are unfortunately wanting, and the evidence is confined to the collection of a number of cases in which death and reproduction take place nearly or quite simultaneously. These would prove nothing, even if post hoc were always propter hoc; and there are, opposed to them, a number of cases in which reproduction and death take place at different times. In obtaining evidence for ‘the fatal influence of reproduction,’ is it possible to point to every case of sudden death after the act of oviposition or fertilization? These cases occur among many of the higher animals, especially in Insects, and were collected by me in an earlier work[[79]]. It is obvious that such cases are exceptional, but in a restricted sense it is quite true, as far as these individual instances are concerned, that death appears as a consequence of reproduction. The male bee, which invariably dies while pairing, is undoubtedly killed in consequence of a very powerful nervous shock; and the female Psychid, which has laid all her eggs at once, dies of ‘exhaustion’—however we may attempt to explain the term on physiological principles.
Can we conclude from these cases that the effects of reproduction are, in Götte’s sense, universally fatal; that reproduction is the positive and ‘exclusive explanation of natural death’? (l. c., p. 32.) I need not linger over these isolated examples, but I turn at once to the foundation of the whole conclusion—a foundation which is obviously unable to support the superstructure erected on it. Götte formally derives the idea that death is a necessary condition of reproduction, from a very heterogeneous collection of facts. When we examine this collection we find that the process which is taken to be death is not the same thing in all these instances, while the same is true of the influence of reproduction by which death is supposed to be caused. The whole conception arises out of the process of encystment, which is regarded as the building-up of reproductive material—that is, as true reproduction; and since, according to Götte’s view, the formation of germs is always intimately connected with an arrest of life, and since, by his own definition, this stand-still of life is equivalent to death, it follows that, with such a theory, reproduction, in its essential nature, must be inseparably connected with death. It is necessary at this juncture to remember what Götte means by the process of rejuvenescence, and to point out that he is dealing with something quite different from ‘the fatal influence of reproduction,’ which was just now mentioned with regard to insects. ‘Rejuvenescence,’ bound up as it is with encystment and reproduction, is, according to Götte, ‘a re-coining of the specific protoplasm, by means of which the identity of its substance is fixed by heredity,’ a ‘marvellous process in which phenomena the most important in the whole life of the animal, and in fact of all organisms—reproduction and death—have their roots’ (l. c., p. 81). Whether such re-coining really takes place or not, at any rate I claim to have shown above that it does not correspond with death in the Metazoa, and—if it is represented at all in these latter—that it ought to be looked for in the reproductive cells; and indeed, in another passage, Götte himself has placed the process in these cells.
While, among the Monoplastids, according to Götte, the causes of the supposed death lie hidden in this mysterious change of the organism into reproductive material, Götte asserts that among the Polyplastids (such as Magosphaera, hypothetically perfected so as to form a genuine Polyplastid), the causes of death operate so that the organism breaks up into its component cells, all these being still reproductive cells—a process which, unlike ‘rejuvenescence,’ has nothing mysterious about it, and which is certainly not genuine death. In the Orthonectid-like animals death does not occur as a consequence of the dispersal of the reproductive cells, but rather because the part of the animal which remains is so small and effete that, being unable to support itself, it necessarily dies. From this point at least the object of death and the conception of it remain the same, but now the idea of reproduction undergoes a change. When the Rhabdite females of Ascaris are eaten up by their offspring, is this mode of death connected with the ‘rejuvenescence of protoplasm’? (l. c., p. 34.) Is there any deep underlying relationship between such an end and the essential nature of reproduction? The same question may be asked with regard to the ‘Redia or the Sporocyst of Trematodes, which are converted into slowly dying sacs during the growth of the Cercariae within them.’ We cannot speak of the ‘fatal influence of reproduction’ among tape-worms just because ‘in the ripe segments the whole organization degenerates under the influence of the excessive growth of the uterus.’ It certainly degenerates, but only so far as the developing mass of eggs demands. In fact, at a sufficiently high temperature, death does not occur, and such mature segments of tape-worms creep about of their own accord. We cannot fail to recognize that in this as well as in the above-mentioned cases we have to do with adaptation to certain very special conditions of existence—an adaptation leading to an immense development of reproductive cells in a mother organism which can no longer take in nourishment, or which has become entirely superfluous because its duty to its species is already fulfilled. If this is an example of death inherent in the essential nature of reproduction, then so is the death of a mature segment of a tapeworm in the gastric juices of the pig that eats it.
With Götte, the conception of reproduction, like the conception of death, is a protean form, which he welcomes in any shape, if only he can use it as evidence. If death is a necessary consequence of reproduction, its cause must be always essentially the same, and might be expressed in one of the following suggestions:—(1) in the necessity for a ‘re-coining’ of the protoplasm of the germ-cells; but here death could only affect the germ-cells themselves: (2) perhaps in the withdrawal of nourishment by the mass of developing reproductive material, just as death occurs sometimes among men by the excessive drain on the system caused by morbid tumours: (3) or in consequence of the development of the offspring in the body of the mother; this however would only affect the females, and could therefore have no deep and general significance: (4) from the extrusion of the sexual cells,—ova or spermatozoa,—and in the impossibility of further nourishment which is consequent upon this extrusion—(Orthonectides?): or (5) finally in an excessively powerful nervous shock brought about by the ejection of the reproductive cells.
But no one of these alternatives is the universal and inevitable cause of death. This proves irrefutably that death does not proceed as an intrinsic necessity from reproduction, although it may be connected with the latter, sometimes in one way and sometimes in another. But we must not overlook the fact that in many cases death is not connected with reproduction at all; for many Metazoa survive for a longer or shorter period after the reproductive processes have ceased.
In fact, I believe I have definitely shown that no process exists among unicellular animals which is at all comparable with the natural death of the higher organisms. Natural death first appeared among multicellular beings, and among these first in the Heteroplastids. Furthermore, it was not introduced from any absolute intrinsic necessity inherent in the nature of living matter, but on grounds of utility, that is from necessities which sprang up, not from the general conditions of life, but from those special conditions which dominate the life of multicellular organisms. If this were not so, unicellular beings must also have been endowed with natural death. I have already expressed these ideas elsewhere[[80]], and have briefly indicated how far, in my opinion, natural death is expedient for multicellular organisms. I found the essential reason for confining the life of the Metazoa to a fixed and limited period, in the wear and tear to which an individual is exposed in the course of a life-time. For this reason, ‘the longer the individual lived, the more defective and crippled it would become, and the less perfectly would it fulfil the purpose of its species’ (l. c., p. 24). Death seemed to me to be expedient since ‘worn-out individuals are not only valueless to the species, but they are even harmful, for they take the place of those which are sound’ (l. c., p. 24).