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.

This association of pigmentation and sexual aptitudes has been recognized in the popular lore of some peoples.  Thus the Sicilians, who admire brown skin and have no liking either for a fair skin or light hair, believe that a white woman is incapable of responding to love.  It is the brown woman who feels love; as it is said in Sicilian dialect:  “Fimmina scura, fimmina amurusa."[164]

The dependence of pigmentation upon the sexual system is shown by the fact that irritation of the genital organs by disease will frequently suffice to produce a high degree of pigmentation.  This may the neck, the trunk, the hands.  Simpson long since noted that uterine irritation apart from pregnancy may produce pigmentation of the areolae of the nipples (Obstetric Works, vol. i, p. 345).  Engelmann discussed the subject and gave cases, “The Hystero-Neuroses,” pp. 124-139, in Gynaecological Transactions, vol. xii, 1887; and a summary of a memoir by Fouquet on this subject in La Gynecologie, February, 1903, will be found in British Medical Journal, March 28, 1903,

Of all physical traits vigor of the hairy system has most frequently perhaps been regarded as the index of vigorous sexuality.  In this matter modern medical observations are at one with popular belief and ancient physiognomical assertions.[165] The negative test of castration and the positive test of puberty point in the same direction.