Man is a placentary mammifer: by this title his genital organs and their mode of employ are common to him and to all hairy animals having teats and an umbilicus. He is not normally covered all over with hair, but there is hardly a spot on his body where hairs may not sprout, and both sexes are hairy often with extreme abundance in pubis and arm-pits. The male and active organ of mammifers is the penis, usually completed exteriorily by the testicles. The penis is, at once, the excreting _conductor_ of urine and sperm; an analogous relation exists in the female, and it is with exactitude that these mingled organs have been called genito-urinary or more recently, uro-genital; it is the same in all the animal series, the urethra opens exteriorily or it ends, as in birds, in a cloaca, vestibule, for all the excretions. The penis of two-handed (bimanous) creatures descends freely, it hangs before the pubis in quadrumanes, and in chiroptera (bats). The bat is strangely like man, and like primates in general: five fingers to the hand, one a thumb, five fingers on the foot, pectoral teats, mensual flux, free penis; it is a little caricature of man, abrupt and frightened in its evening flight about houses. Among flesh-eaters, ruminants, pachyderms, solipedes and several other families of mammals, the penis is sheathed in a scabbard which stretches along the belly; thus preserved against accidents and insect stings, while its sensibility is maintained intact. Voyagers, according to Buffon, have seen Patagonians trying to get like results by tying the 'foreskin above the gland, like a bag with a cord. Thus man's hand permits him to improve or mutilate his body. Mutilation and sexual deformations, circumcision among Semites and savages, excision of Russian illuminati, transversal perforation of the gland, surgical flattening of the prong, are very frequent. The hand of the chiroptera is shackled, that of quadrumanes has only one sexual rôle, masturbation. It may also serve as a shield against external danger; many quadrumanes, better protected, make the same use of their tail when they curl it between their legs, this is sometimes a psychological gesture, female modesty or refusal, sometimes a gesture of preservation. The movements of Venus modest, of man coming naked from his bath, have no other origin. Monkeys when they stop moving about, place their hands on their sexual parts. The Polynesians, before Christianity, had the custom when standing upright, of holding their scrotum in both hands with the prong hanging between the fingers: the posture of the wild dandy. Certain species lack scrotum as Pliny had already remarked: _Testes elephanto occulti_. In camels the testicles roll beneath the skin of the groin; rats' testicles are internal, but emerge in the rutting season and assume an enormous development. Apes often have the pouch-skin blue, red or green, like the other bald parts of their bodies.