CHAPTER IX 



HEREDITY AND SEX 



In all the cases discussed hitherto the characters 

 considered have been transmitted independently of 

 the sex of the parents or offspring. The results of 

 reciprocal matings have been identical, and the 

 distribution of the characters among the offspring 

 has been independent of their sex. It is well 

 known, however, that many characters, in animals 

 especially, are confined to one sex or are developed 

 differently in males and females; this is most con- 

 spicuously so in 'secondary sexual characters,' that 

 is to say, features characteristic of one sex only but 

 not in any way directly connected with reproduction. 

 As examples may be mentioned the distinctive 

 plumage of many male birds, or patterns of butter- 

 flies, the horns of male mammals, and the hair on 

 the face in men. Darwin long ago showed that 

 such distinctively male characters may be transmitted 

 through the female, and it has recently been shown 

 that for Pheasants the converse is also true. Before 



