case of human beings, in which our interest is greatest, to
take an example, it will be found that the most womanly
woman has a growth of colourless hair, known as "lanugo"
in the position of the male beard; and in the most manly
man there are developed under the skin of the breast masses
of glandular tissue connected with the nipples. This condition
of things has been minutely investigated in the true
genital organs and ducts, the region called the "urino-genital
tract," and in each sex there has been found a complete
but rudimentary set of parallels to the organs of the other
sex.
These embryological conclusions can be brought into relation with another set of facts. Haeckel has used the word "gonochorism" for the separation of the sexes, and in different classes and groups of creatures different degrees of gonochorism may be noted. Different kinds of animals and plants may be distinguished by the extent to which the characters of one sex are rudimentary in the other. The most extreme case of sexual differentiation, the sharpest gonochorism, occurs in sexual dimorphism, that is to say, in that condition of affairs in which (as for instance in some water-fleas) the males and females of the same species differ as much or even more from each other as the members of different species, or genera. There is not so sharply marked gonochorism amongst vertebrates as in the case of Crustacea or insects. Amongst the former there does not exist a distinction between males and females so complete as to reach sexual dimorphism. A condition much more frequent amongst them is the occurrence of forms intermediate in regard to sex, what is called abnormal hermaphroditism; whilst in certain fishes hermaphroditism is the normal condition.
I must point out here that it must not be assumed that there exist only extreme males with scanty remnants of the female condition, extreme females with traces of the male, hermaphrodite or transitional forms, and wide gaps between these conditions. I am dealing specially with human beings, but what I have to say of them might be applied, with more
