198 Evolution and Adaptation 



A remarkable bird of South America, the bell-bird, has a 

 peculiar note that "can be distinguished at the distance of 

 nearly three miles and astonishes every one who hears it. 

 . . . The male is pure white, whilst the female is dusky- 

 green ; and white is a very rare color in terrestrial species 

 of moderate size and inoffensive habits. The male, also, as 

 described by Waterton, has a spiral tube, nearly three inches 

 in length, which rises from the base of the beak. It is jet- 

 black, dotted over with minute downy feathers. This tube 

 can be inflated with air, through a communication with the 

 palate ; and when not inflated hangs down on one side. The 

 genus consists of four species, the males of which are very 

 distinct, whilst the females, as described by Mr. Sclater in a 

 very interesting paper, closely resemble each other, thus offer- 

 ins: an excellent instance of the common rule that within the 

 same group the males differ much more from each other than 

 do the females. In a second species (C. nudicollis) the male 

 is likewise snow-white, with the exception of a large space of 

 naked skin on the throat and round the eyes, which during 

 the breeding season is of a fine green color. In a third 

 species (C. tricarunculatus) the head and neck alone of the 

 male are white, the rest of the body being chestnut-brown, 

 and the male of this species is provided with three filamentous 

 projections half as long as the body — one rising from the 

 base of the beak, and the two others from the corners of the 

 mouth." 



The most familiar case of sexual difference amongst North 

 American birds is that of the scarlet tanager, in which the 

 male is scarlet with jet-black wings, while the female is an 

 inconspicuous yellow-green color. Amongst domesticated 

 animals the peafowl shows the most beautiful case of sexual 

 differences. The magnificent tail of the male can be lifted 

 up, so as to be seen to best advantage when the male faces 

 the observer. Moreover the wild form, living in the forests 

 of India, has the same gorgeous train. 



