Fish are the only vertebrates among whom one encounters hermaphrodism, either accidental: cyprins, herrings, scombers; or regular, sargue, sparaillon, seran. The myxines, very humble fish living as parasites, are alternative hermaphrodites, like oysters, like ascides; the genital gland functions first as testicle, then as ovary. The amphioxus, the bridge between invertebrates and vertebrates, is not hermaphrodite. The most strongly marked and most complicated forms of hermaphrodism are found in mollusks, and chiefly in gasteropodes. The alternate hermaphrodism of oysters produces effects which have been observed throughout antiquity. The advice to abstain from oysters during months lacking an "r" is based on a fact, and that fact sexual. From September to May, they are males, they are testicles, they elaborate sperm, they are good; from June to August the ovaries bourgeon, fill with eggs which turn whitish as they ripen, the oysters are females, they are bad; fecundation takes place at this time, the spermatozoides, born in the preceding period, finally perform their office. Superstitions before being rejected ought to be minutely observed and analysed, there is nearly always a kernel of truth in the gross envelope. In the hermaphrodism of echinoderms, of fish, there is never auto-fecundation; either the sexual products meet outside the animals, which have neither copulating organs, nor a related genital life; it is a simple growth of germs; or, in a more complex phase the individuals have exterior male organs, and female organs, but they can not use them without the aid of another individual acting either as male, or as female. Here a new distinction is imposed: either the animal will be successively male, and then female; or it will be both at once. This union of the two sexes seems useless, according to human logic, when the two genital glands ripen at different seasons; one understands it better when the reciprocal fecundation is simultaneous, since this doubles the number of females and better assures the conservation of the specie. One must set aside the idea of pleasure. Apart from the fact that we can judge it only by a very distant and even dubious analogy considering the difference between the nervous systems of man and mollusk, one must set it aside as useless. Pleasure is a result not an aim. In most animal species coition is but a prelude to death, and often love and death work their supreme act in the same instant. Copulation of insects is suicide: would it be reasonable to consider it as produced by a desire to die? One must dissociate the idea of pleasure and the idea of love, if one wants to understand anything of the tragic movements which perpetually beget life at the expense of life itself. Pleasure explains nothing. People might simply be commanded to die as a means of reproduction, they would obey with the same eagerness: this is observed even in humanity. Dithyrambs on