If there is no general rule, if there is no one moral manner of fecundating a female, one must recognize that the same mode is fixed in the same specie, in the same genus or family. I do not think that anyone has observed variation in the sexual habits of an animal; yet acts of sheer disembarrassment being possible, one can not consider the love method as being rigorously fixed. It has varied in social bees, parting from the relation of the couple, the aggression of the male, to end in the political and autocratic fecundation of a sole female by a sole male chosen among an hundred slave favourites. The mechanism itself must have changed with the change of the organs, complying with corporal circumstances and with those of the milieu, under pressure of the nervous system which demands acts without caring for the instruments which must execute them. One finds proof of these changes in the accidental hermaphrodism of a great number of invertebrates and even of fishes, such as the cod, the herring, the scomber: a fundamental change since it shifts the animal from a superior to an inferior category; a recall to origins, doubtless, and an indication that the species liable to such accidents are far from being physiologically fixed. It is very probable that analogous accidents, less accentuated, visible sometimes in exterior malformation, invisible in their psychological influence, are the cause of certain tendencies in contrast to the sex apparent or even real. But this does not yet answer the main question: are there in animals, apart from purely mechanical aberrations, erotic fantasies? One can not answer with certainty. The animal merely follows a groove; when he has gone through it, if he lives for another season, he merely goes over the same ground, attentive to the same need, submitted always to the same gestures. Very true, but the animals familiar to man or his neighbours, the dog, the ape, perhaps the cat, are assuredly capable of erotic fantasies; it is therefore difficult to deny this tendency to other animals, to the so intelligent hymenoptera, for example. Who knows, moreover, whether certain eccentric modes of copulation are not fixed fantasies, become habit and having supplanted an anterior method, the animal being little able to employ two customs at once? What we have found, at least, is that the love mechanism is, in nature, of infinite variety, and that if it appears stable in most of the fixed species, it is, in its entirety extremely oscillating, capricious, and fantastic. [1] The name of these cirripedes bears witness to this superstition: _anatife_ is the abridgement of _anatifere_, duck-bearing, latin _anas, anatis_, "A tree equally marvelous, is that which produces barnacles, for the fruits of this tree change into birds." (Mandeville's Travels.)