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 lay eggs whence come nothing but females, unless the eggs are subjected to a temperature above 18 degrees (centigrade); above that the eggs hatch out males. Between the periods of coupling there are long stretches of virgin-birth, nothing but females producing females, until the temperature permits a male hatch. In two years the plant louse runs through ten or twelve parthenogeneses; in July of the second year, there appear winged individuals, these are still female, but double size, and they lay two sets of eggs, whereof the smaller hatch male (the male is three or four times smaller than the female), the larger eggs hatch female; there is coupling and the cycle begins again.

For long people believed the plant louse truly androgynous. Réaumur and Bonnet, having seen isolated plant-lice reproduce themselves were convinced of this, when Trembley, a man of genius, celebrated also for his observations of hydra, threw out the idea: Who knows whether a coupling of these lice does not fecundate them for several generations? He had discovered the basis of parthenogenesis. Facts upheld him. Bonnet described the male and female, and noted even the genital ardour of this sticking leaf-louse, this milch-cow of the ants.

Parthenogenesis is a sign-post. Nothing more clearly demonstrates the importance of the male or the precision of his function. The female appears to be the whole show, without the male she is nothing. She is the machine and has to be wound up to go. The male is merely the key. People have tried to obtain fecundation by false keys. Eggs of sea-anemones, and star-fish have been hatched by contact with exciting chemicals, acids, alkalines, sugar, salt, alcohol, ether, chloroform, strychnine gas, carbonic acid. But one has never been able to bring these scientific larvæ to maturity, and everything leads one to believe that if one succeeded, and that if these artificial beings were capable of reproduction, it would be but for a limited period. This provoked parthenogenesis is neither more nor less interesting than the normal. It is doubtless abnormal, but abnormal parthenogenesis is not infrequent in nature; eggs of the bombyx, of star-fish, and of frogs, hatch sometimes without fecundation, and