cells, and so forth, until the whole animal is built up and is ready for birth. One point of cardinal importance must here be noted. The originating cell, as we have seen, has eight of its sixteen chromosomes from one parent and eight from another. When division takes place, these chromosomes, as we have seen, split longitudinally, and the result is that each new cell gets exactly the same mixture of chromatin as that of the originating cell—half from each parent. This principle of division is carried on throughout the whole process of building up the new being—every cell of the latter, down to the minutest details of its structure, containing an exactly equal quantity of hereditary elements from each of its parents.
It will be seen from the above account that the old conception of the germ-cell as a passive body, incapable of a change till ‘fertilized’ by a male or sperm cell, was altogether wrong. Both male and female cells prepare themselves for conjugation long before it takes place, and neither of them can be said to be a more active agent in fertilization than the other. Not ‘fertilization’ but ‘fusion’ is the keyword of the process. The mystical conception, as old as Plato, of the male and female as representing respectively the two halves of a complete being, turns out to be no poetic metaphor. As regards the essential features of reproduction, it is a literal fact.
If we now ask why and by what mysterious law all these exact and elaborate choric movements take place Weismann and his school refer us to “chemotactic forces,” the nature of which is yet unknown. Chemotaxis means simply the effect of the presence of certain substances on vital organisms without specific chemical action. The really essential fact is that these special chemotactic forces are working in living protoplasm. Life is not the product or the slave of any chemotactic forces, but their maker and steersman.
The following passage from a work of the late Prof. Geo. Rolleston may be pertinently quoted here:—
“There exists, as is well known, a tendency to resolve all physiological into physico-chemical phenomena: undoubtedly many have been, and some more may still remain to be, so resolved; but the public may rest assured that in the kingdom of Biology no desire for a rectification of frontiers will ever be called out by any such attempts at, or successes in the way of, encroachment; and that where physics and chemistry can show that physico-chemical agencies are sufficient to account for the phenomena, there their claim upon the territory will be acceded to, as in the cases we have been glancing at [certain animal poisons], and where such claims cannot be established and fail to come up to the quantitative requirements of strict science, as in the cases of continuous and of discontinuous development or self-multiplication of a contagious germ, and in some others, they will be disallowed.”45
This was written in 1870. A generation later the attempt to reduce life to a physico-chemical phenomenon had not made much way, as may be judged by the following passage from Strasburger’s Text Book of Botany:—46
“Vital phenomena are essentially bound up with the living protoplasm. No other substance exhibits a similar series of remarkable and varied phenomena, such as we may compare with the attributes of life. As both physics and chemistry have been restricted to the investigation of lifeless bodies, any attempt to explain vital phenomena solely by chemical and physical laws could only be induced by a false conception of their real significance, and must lead to fruitless results. The physical attributes of air, water, and of the glasses and metals made use of in physical apparatus, can never explain qualities like nutrition, respiration, growth, irritability and reproduction.”
And Wilson concludes his work by the admission that
“the study of the cell has on the whole seemed to widen rather than to narrow the enormous gap that separates even the lowest forms of life from the inorganic world.”47
“The lowest observed forms of life” would have been a more exact way of stating the fact.
Many questions of detail will occur to the reader at this point, which he will find answered in the pages of Weismann or other investigators. Here we must confine ourselves to what has a distinct bearing on the objects of this study. One of the points which may be briefly touched on is the question how it comes that two germ cells, once having passed through their maturation divisions, cannot fuse and form a new being; nor can two sperm cells. Were this possible we might have ‘self-fertilization,’ and virginal conception or parthenogenesis, whenever two germ cells in the ovary of a female animal or in that of a plant happened to come into contact. But since the object of fusion is the union of (more or less) unlike, and not closely related, elements, we find that even when a kind of self-fertilization occurs, as in some plants, the sperm or pollen cells are differentiated visibly, and probably still more invisibly, from the germ cells. But, apart from this, the object of preventing the union of reproductive cells of the same sex is mechanically attained by a very curious device. The cell-organ by which division is carried out is the centrosome. But in the course of the two maturation divisions of the germ cell, that cell loses its centrosome, which seems to be absorbed into the protoplasmic substance of the cell when once its task is accomplished. No fusion of any number of such cells can therefore lead to any further change or growth, for growth is based on cell division, and the centrosome is the organ of division. The sperm cell, on the other hand, does not lose its centrosome; it retains it to form the organ of division for the new cell after conjugation. But, reduced as it is to little more than a bare nucleus without any envelope of nutritive matter, the sperm cell cannot support the intense vital activity called for in the initial stages of the life of a new being, and therefore sperm cells, like the germ cells, though for a different reason, would be incapable of mutual conjugation, even if the element of mutual attraction existed among them.
Another point of interest is the question of the determination of sex. The known facts afford a strong corroboration of the general theory of reproduction outlined above. It has not been ascertained, nor is it, perhaps, ascertainable, whether the sperm cells of the male contain in their chromatin a preponderance of male, while the germ cells provide chiefly the female determinants.48 However this may be, it is certain that determinants which severally control the formation both of male and of female structure are always present in every combination of the sperm and germ cells, those which exhibit the greatest energy and vitality probably prevailing in the determination of the sex of the future being. This accounts at once not only for the cases (rare in the higher animals) of actual hermaphroditism, when the sex is really indistinguishable, but for the universal occurrence in all male animals of rudimentary female organs (such as mammæ) and in all females of rudimentary male organs. Both sets of determinants are always present; the more powerful prevail, but the weaker have a deflecting influence on the total result. When the primary sexual characters of the embryo are determined, they appear to communicate a stimulus which starts into activity the appropriate secondary characters, such as colouring and other modifications not directly sexual. An extraordinary case, which I take from Beddard’s Animal Coloration,49 is that of a chaffinch which was found to have on the left side of its body the plumage of a hen bird and on its right that of a cock. On dissection the meaning of this freak of physiology was revealed. The bird was an hermaphrodite, having the female organs of generation on the left side of its body and the male on the right. Hermaphroditism is not in itself a very uncommon phenomenon in birds (though here it is a monstrosity, not, as in slugs and snails, a natural and useful condition); but the way in which in this instance it governed the distribution of colour is most peculiar; and of course it strongly reinforces Weismann’s conception of distinct determinants for the various details of bodily structure.50
This brings us to the recognition of a competition among determinants which is an important, indeed a cardinal, feature in Weismann’s theory of evolution. He makes, as I am forced to believe, an illegitimate and extravagant use of it, but the principle may really exist and be operative without furnishing the master-word to the riddle of organized being. The master-word, as I shall try to show, is nature’s will to live. But before going fully into this argument, let us fix in our minds the rationale
