194 Evolution and Adaptation 



extreme beauty of certain species ; for instance, of the coral- 

 snakes of South America, which are of a rich red with black 

 and yellow transverse bands." 



In lizards the erectile crests of the male Anolis, the brilliant 

 throat patches of Sitaria minor, which is colored blue, black, 

 and red, the skinny appendages present on the throat of the 

 little lizards of the genus Draco, which in the beauty of their 

 colors baffle description, are given as cases of sexual adorn- 

 ment. In the last case cited the ornaments are present, 

 however, in both sexes. The remarkable horns in the males 

 of different species of chameleons are imagined to have been 

 acquired through the battle of the males with each other. 



In the group of birds we find some of the most striking 

 cases of secondary sexual differences. The spurs, combs, 

 wattles, horns, air-filled sacs, topknots, feathers with naked 

 shafts, plumes, and greatly elongated feathers are all second- 

 ary sexual characters. The songs of the males, the rattling 

 together of the quills of the peacock, the drumming of the 

 grouse, and the booming sounds made by the night jars 

 while on the wing, are further examples of secondary sex- 

 ual differences. The odor of the male of the Australian 

 musk duck is also put in the same category. 



The pugnacity of many male birds is well known, and it is 

 imagined that one of the results of the competition of the 

 individuals of the same sex with each other has led to the 

 development of the organs of defence and offence. The 

 males that have been successful in these battles are then sup- 

 posed to mate with the best females. In this way those 

 secondary sexual differences, connected with the encounters 

 of the males, are supposed to have been formed. Darwin 

 states in this connection : — 



" Even with the most pugnacious species it is probable 

 that the pairing does not depend exclusively on the mere 

 strength and courage of the male ; for such males are gener- 

 ally decorated with various ornaments, which often become 



