and to this end all means are, to her, good. But if she presents us the laborious example of the bee, she does not hide from us the polyandrous example, nor the cruel amours of the mantis. There is not in the will to live the faintest trace of our poor little human morality. If one wishes an unique sole morality, that is to say an universal commandment, which all species may listen to, which they can follow in spirit and in letter, if one wishes in short to know the "aim of life" and the duty of the living, it is necessary, evidently, to find a formula which will totalize all the contradictions, break them and fuse them into a sole affirmation. There is but one, we may repeat it, without fear, and without allowing any objection: the aim of life is life's continuation.
CHAPTER III
SCALE OF SEXES
Asexual reproduction.—Formation of the animal colony.—Limits of asexual reproduction.—Coupling.—Birth of the sexes.—Hermaphrodism and parthenogenesis.—Chemical fecundation.—Universality of parthenogenesis.
The primitive mode of reproduction is asexual, or what one will so consider provisorily, in comparison with more complex mechanism. In the first living forms there are neither sexual organs nor differentiated sexual elements. The animal reproduces itself by scissiparity or by budding; the individual divides itself in two parts, or a protuberance develops, forms a new being and then separates.
Scissiparity is an inexact term, for the division is transversal, and the two parts far from equal; it occurs in protozoaires, and further in worms, star-fish and polyps. Budding is common to protozoaires, infusoria, cœlenterata, to fresh-water polyps and to nearly all vegetables. A third primitive mode, sporulation, consists in the production inside the organism of particular cells, spores, which separate and become individuals; this occurs in protozoaires, as well as in ferns, algæ and mushrooms.
The first two modes, division and budding, serve also for the formation of animal colonies, when the new individual retains a point of contact with the generating individual. It is by this notion of colony that one explains complex beings, and even superior animals, in considering them as reunions of simple primitive beings which have differentiated themselves and still retained a solidarity, sharing the physiological work between them. Colonies of protozoaires are formed of individuals having identical functions, living in perfect equality, despite the hierarchy of position; colonies of metazoaires are composed of specialised members whose separation may be a cause of death for the total individual. There is then, in the latter case, a new being composed of distinct elements which, retaining a certain essential autonomy, have become the organs of a new entity.
The first living organisms formed their hierarchies thus: individual unicellular, or plastide; group of plastides or meride. The merides, as the protozoaires, can reproduce themselves asexually, or by division or budding. They may separate completely or remain attached to their generator. If they remain attached one has mounted a step and attained the zoide. Thence, by colonies of zoides one gets individuals still more complex, called demes. None of these terms is much more than a convenience for memory. The nomenclature stops, as does the progression, at a certain moment, for the evolution has its limit, its finality, as does even the milieu in which life continues to evolve. One might say that heaving up from the obscure vital centre, the new animal-shoots branch upward until they knock their heads upon an ideal or imaginary roof which prevents any further climbing. This is the death of the species, and Nature contemptuously abandoning her work, begins to mate yet another mould of the initial ooze, to derive from it a new form. The dream of an unlimited transformation of actual species is pure chimæra; they will disappear one by one, according to their order of primogeniture, according to their faculty for adapting themselves to the changing milieu, and one might foresee, if the earth lasts, in a distant time an unimaginable fauna replacing the present fauna, and even replacing man.
Man is a metazoaire, that is to say an animal with differentiated pluricellules, like the sponge, the wheel animals, and the annelids. He belongs to the artizoaire series: a head, belly, back, bilateral symmetry; to the vertebrate branch: internal skeleton, cartilaginous and osseous; to the class of mammifers, to the sub-class of placentaires; to the group of primates not far from the chiroptera (bats) and the rodents.
In regard to the life-transmitting mechanism the animals are divided somewhat differently. On one side budding and division, or scissiparity, is prolonged rather far into the metazoaire series concurrent with sexual reproduction; on the other hand there are, among protozoaires, phenomena of coupling, unions of cellules which resemble veritable fecundation and perform its rôle; without the nuclear regeneration which is the aim and consequence, neither segmentation nor budding can take place, at least not indefinitely. In sum, the reproduction of beings is always sexual; only in the one case, the protozoaires, it is produced by non-differentiated elements; and in the other, the metazoaires, by differentiated elements, a male and a female. If one clips off bits of a sponge, a hydra, one obtains as many new individuals, which when they have grown one may again divide, and so on repeatedly, but not indefinitely. At a variable instant, after a certain number of generations by fragmentation, senescence appears among the so produced individuals; the clipped morsels remain inert. Thus this sort of artificial virgin birth has a limit, as has normal parthenogenesis, and in order that the individuals may regain their parthenogenetic force one must give them time to regenerate their cellules by the coupling which fecundates them.
Fecundation is in all cases, doubtless, merely a rejuvenation, thus considered it is uniform not only throughout the animal series, but throughout the vegetable. One ought to experiment in slip-cutting, and discover at what point the slip cut from a slip begins to diminish in vitality. Coupling and fecundation have the same result: it is necessary that cellules A unite with cellules B (macro-nucleus and micro-nucleus among protozoaires; ovule and spermatozoid among metazoaires), in order that the organism may usefully exteriorize a part of its substance. When the too complex organism has lost the primitive faculty of segmentation, it makes use, directly, to reproduce itself, of certain cellules differentiated for that purpose: it is these cellules united into a whole, which reintegrate and give birth to a double of the generating individual or individuals. From the top to the bottom of the sexual scale the new being springs invariably from a duality. The multiplication takes place only in space. In time the product is a contraction, two giving one.
Scissiparity is compatible with the existence of separate sexes, as in the starfish. This fantastic animal with no instrument save its suckers opens oysters, envelops them with its stomach which it unbellies (vomits), devours them. It is not less curious in reason of its variety of reproductive mode, serving itself of sexual apparatus, or budding, or casting an arm which becomes a new creature. Thus it is difficult to class animals according to their manner of reproduction; hermaphrodism is another block. This mode is doubtless primitive, since it is of the type of protozoaire coupling, but it is greatly complicated when it persists, for example up to the moment where it disappears in the mollusk series, whereof some possess so luxurious a love-organism. The simple and very naive form, that in which the sperm and the eggs are produced simultaneously inside the same individual, is found only in inferior organisms. Normal parthenogenesis belong equally to summary and to complicated animals, to wheel-animals and to bees. Among arthropodes, that is to say among insects in general, the sexes are always separate, save in certain tardigrade arachnids, but these are the ones which offer the finest cases of parthenogenesis, generation without aid of the male. The term need not be taken literally. For as there is no indefinite scissiparity without coupling, there is no unlimited parthenogenesis without fecundation: the female is fecundated for several generations which transmit this power, but there comes a day when the female who has not encountered a male gives birth to males and females. They couple and produce females parthenogenetically endowed. This has been for long time a mystery—it is still a mystery, for side by side with normal parthenogenesis there is irregular parthenogenesis, there are cases where non-fecundated eggs behave exactly as fecundated eggs, without anyone's knowing why.
The virgin-begotten cycle of plant-lice is famous, that of wheel-animals not less entertaining. The males, smaller than the females, live but two or three days, couple and die. The fecundated females