The penis is found in woman in the form of clitoris. This is almost as voluminous as a true penis in quadrumanes; it is atrophied in other species. It varies individually in women, certain of them being in this respect quadrumanes. Sometimes the clitoris is pierced for the passage of the urethra (certain apes and the mole); a slight trace of this meatus is seen at the head of the woman's clitoris. In species whose males possess a penial bone the female has often a clitoridian bone; nothing more clearly affirms the parallelism of these two organs, whereof one serves only for pleasure, after having been, perhaps in a long distant era, when man romped among marine invertebrates, a real instrument of fecundation. The greater labia, limiting the general orifice of the vulva, exist only in woman and, less markedly, in the female orang-outang. Circular in rodents, transversal in the unique case of the hyena, a heteroclite animal, the vulva is longitudinal in all other mammifers. Completely imperforate in the mole the vagina is more or less closed by a membrane, which the male penis tears in first encounter, in women, and several quadrumanes, certain small monkeys, the marmoset, certain carnivora, the bear, hyena, white-bellied seal, the daman (nailed); it is replaced in dog, cat, ruminants by an annular gripping between the vagina and the vestibule. The maidenhead is, therefore, not peculiar to human virgins, and there is no glory in a privilege which one shares with the marmoset. Menstruation is found in quadrumanes, in bats; other female mammals show an emission of blood, which is, however, limited to the rutting season. The position of teats is variable, as also their number, they are in the groin in ruminants, solipedes, cetaces; ventral in dogs, pigs; pectoral and always two in nearly all primates, chiroptera, elephants, and sirenians, who for this reason, doubtless, reminded the sailors of the ancient world of their women. Other particularities and correspondences are examined in the next chapter which deals with the mechanism of love, and the method used by divers animals to make use of their organs according to the commandment of nature. There remain for consideration the lesser mammals and other vertebrates whose fecundatory instruments resemble those of mammifera.