The connection between pigmentation and sexual activity is very ancient. Even leaving out of account the wedding apparel of animals, nearly always gorgeous in scales and plumage and hair, the sexual orifice shows a more or less marked tendency to pigmentation during the breeding season from fishes upward, while in mammals the darker pigmentation of this region is a constant phenomenon in sexually mature individuals.[159] In the human species both the negative standard of castration and the positive standard of puberty alike indicate a correlation of this kind. Those individuals in whom puberty never fully develops and who are consequently said to be affected by infantilism, reveal a relative absence of pigment in the sexual centers which are normally pigmented to a high degree.[160] Among those Asiatic races who extirpate the ovaries in young girls the skin remains white in the perineum, round the anus, and in the armpits.[161] Even in mature women who undergo ovariotomy, as Kepler found, the pigmentation of the nipples and areola disappears, as well as of the perineum and anus, the skin taking on a remarkable whiteness. Normally the sexual centers, and in a high degree the genital orifice, represent the maximum of pigmentation, and under some circumstances this is clearly visible even in infancy. Thus babies of mixed black and white blood may show no traces of negro ancestry at birth, but there will always be increased pigmentation about the external genitalia.[162] The linea fusca, which reaches from the pubes to the navel and occasionally to the ensiform cartilage, is a line of sexual pigmentation sometimes regarded as characteristic of pregnancy, but as Andersen, of Copenhagen, has found by the examination of several hundred children of both sexes, it exists in a slight form in about 75 per cent. of young girls, and in almost as large a proportion of boys. But there is no doubt that it tends to increase with age as well as to become marked at pregnancy. At puberty there is a general tendency to changes in pigmentation; thus Godin found that in 28 per cent, adolescent changes occurred in the eyes and hair at this period, the hair becoming darker, though the eyes sometimes become lighter. Ammon, in his investigation of conscripts at the age of 20 (_post_, p. 196), discovered the significant fact that the eyes and hair darken _pari passu_ with sexual development. In women, during menstruation, there is a general tendency to pigmentation; this is especially obvious around the eyes, and in some cases black rings of true pigment form in this position. Even the skin of the negro women of Loango sometimes becomes a few shades darker during menstruation.[163] During pregnancy this tendency to pigmentation reaches its climax. Pregnancy constantly gives rise to pigmentation of the face, the neck, the nipples, the abdomen, and this is especially marked in brunettes.