THE EVOLUTION OF SEX 27 



they are rare or absent altogether. In mammals the 

 horns of the male stag are excellent examples of second- 

 ary sexual characters. The male sea cow is much 

 greater in size than the female, and possesses long tusks. 

 The mane of the lion is absent in the lioness. 



FIG. 13. Great bird of Paradise, male and female. 

 (After Elliot.) 



In birds there are many cases in which the sexes differ 

 in color (Figs. 13 and 14). The male is often more 

 brilliantly colored than the female and in other cases 

 the nuptial plumage of the male is quite different from 

 the plumage of the female. For example, the black 

 and yellow colors of the male bobolink are in striking 

 contrast with the brown-streaked female (Fig. 15). 

 The male scarlet tanager has a fiery red plumage with 

 black wings, while the female is olive green. The male 



