142 SEXUAL DIMORPHISM 



in flight, whereas we have no evidence that the modifications 

 arose spontaneously without the physiological influence of 

 the special mechanical irritations. 



Rupieola crocea, described by Darwin as one of the most 

 beautiful birds in the world, also belongs to the Cotingidse. 

 The male is of a splendid orange colour, with some of the 

 feathers truncated and plumose. The female is brownish- 

 green, shaded with red. Probably in this case the pigments 

 are the same in both sexes, as in other species in which the 

 male and female are of different colours. The male Rupieola 

 has a large median crest, which is much less developed in the 

 female. Sir E. Schomburgk has described the systematic 

 display of the male birds before the females, many males 

 assembling to compete with one another, without fighting. 

 The male is stated to spread its wings, throw up its head, 

 open its tail, and hop about ; erection of the crest is not 

 mentioned, but I suspect it is one of the chief actions in the 

 performance. 



In the sub-family Gymnoderinge, which also belongs to the 

 Cotingidse, there are some remarkable unisexual characters in 

 the males. One of the species is the Bell-bird, Chasmorhynchus 

 niveus, which inhabits the forests of Guiana. The female and 

 young male are dusky green, the adult male pure white. 

 The male possesses a fleshy appendage nearly three inches 

 long at the base of the upper mandible, and this is entirely 

 absent in the female. The male utters also a particularly loud 

 clear note, which gave it its popular name. The chief 

 authority for the habits of this bird was, for a long time, 

 Waterton's Wanderings in South America, published in 1825, 

 in which work it is stated that the appendage has a com- 

 munication with the palate, and is erected by inflation with 

 air. It is stated by Evans, 1 I do not know on what 

 authority, that the appendage is erected when the bird utters 



1 Cambridge Natural History, Birds, 189P. 



