THE SEXES AND SEXUAL SELECTION. 7 



eyes and the plain peahen, between the musical powers of 

 male and female songsters, are very familiar facts. Or again, 

 the combs and "gills" of cocks, the "wattles" of turkey-cocks, 

 the immense top-knot of the male umbrella-bird {Cephalopterus 

 ornatiis), the throat-pouch of the bustard, — illustrate another 



Male and Female Blackcocks. 



series of secondary sexual characters. The spurs of cocks and 

 allied birds are the most familiar illustrations of weapons used 

 by the males in fighting with rivals. As in other animals, it is 

 important to notice that male birds often acquire their special 

 secondary characters, such as colour, markings, and special 

 forms of feathers, only as they approach sexual maturity, and 

 sometimes retain them in all their glory only during the 

 breeding season. 



Among mammals, which stand in so many ways in marked 

 contrast to birds, the law of battle much more than the power 

 of charming decides the problem of courtship. Thus most 

 of the striking secondary characters of male mammals are 

 weapons. Yet there are crests and tufts of hair, and other 

 acknowledgments of the beauty test, while the incense of 

 odoriferous glands is a very frequent means of sexual attrac- 



