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 Azo/s, the brilliant 
throat patches of Széaria 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 
