EVOLUTION OF THE HUMAN EYE 



absent during early youth. Tin's likewise holds good with 

 the mandril and rhesus, in which the face and the posterior 

 parts of the body are brilliantly colored in one sex only." 

 There is no member of the whole class of mammals which 

 shows such resplendent colors as the adult male mandril; 

 they have been compared with those of the most brilliant 

 birds. The following is the description of one of these 

 animals now in the Zoological Society's Gardens: The 

 rather long, harsh hair is dark over the body, but each 

 separate hair is ringed with black and yellow toward the 

 tip, the pattern in certain lights giving a greenish tinge to 

 the fur similar to the shade of other baboons and manv other 



*/ 



African monkeys. On the forehead there is a crest of hair 

 and on the chin a yellow beard. The naked patches on the 

 buttocks are bright red in the adults. On each side of 

 the face, reaching from the eyes to the nostrils, is a cor- 

 rugated swelling, divided into a number of longitudinal 

 ridges. These ridges are bright blue and furrows between 

 them purple. The muzzle, of a bright scarlet, is surrounded 

 by a raised border like that of a pig (see Frontispiece). 



At first it seems strange that the buttocks should be the 

 part of the body which in some monkeys has acquired the 

 most highly decorative color. In a supplemental note 

 "on sexual selection in relation to monkeys" at the con- 

 clusion of his book on The Descent of Man, Darwin brings 

 together evidence to show that monkeys so ornamented 

 are proud of their bright red rumps ; they turn and display 

 them to old friends and new acquaintances as a form of 

 greeting. These naked parts become more turgid and of a 

 brighter color during the season of love ; their display before 

 the female probably acts as a sexual excitement and their 

 proximity to the sexual organs may in this way be explained. 



From the foregoing it will be seen that in mammals as 



