56 SEX 



CHAPTER III 



SEX-CHARACTERS ILLUSTRATED 



Classification of sex-characters Illustrations of sex-char- 

 acters General impressions The general contrast. 



SINCE the beginning of the present century 

 the difficult problem of the origin, develop- 

 ment, and evolution of sex-characters has 

 been illumined by a series of brilliant ex- 

 perimental researches, which have made a 

 reconsideration of the whole subject im- 

 perative. This has been facilitated by the 

 masterly work of Kammerer, who has gathered 

 together the most important data and sub- 

 mitted 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 re- 

 productive organs the ovaries and testes of 

 female and male respectively, which, though 



