Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III SEX-CHARACTERS ILLUSTRATED Classification of sex-characters — Illustrations of sex-characters — General impressions — The general contrast. Since the beginning of the present century the difficult problem of the origin, development, and evolution of sex-characters has been illumined by a series of brilliant experimental researches, which have made a reconsideration of the whole subject imperative. This has been facilitated by the masterly work of Kammerer, who has gathered together the most important data and submitted them to an analysis at once fair-minded and critical. Classification Of Sex-characters. — At many levels in the animal kingdom there are marked differences between the males and females of a species — so marked in some familiar cases that different popular names are applied to the two sexes (e. g. cock and hen, ruff and reeve, stag and hind), so marked in some unfamiliar cases that zoologists have unwittingly named as different species what were afterwards recognised to be but male and female of a single form. When the differences between the sexes are well marked we speak of sex-dimorphism. The contrasted characters that go to constitute sex-dimorphism are of different kinds. They may concern the essential reproductive organs — the ovaries and testes of female and male respectively, which, though arising in the same way in the embryo, may cometo be so different that even on external inspection the two sexes can be distinguished at a glance. Thus in most Mammals the testes are carried in an external pouch or scrotum (into which they descend, as if by a sort of normal rupture, at a certain stage in development), while the ovaries always remain internal. In the second place, the dimorphism may be expressed in conspicuous differences in th...