Chap. XIII. Decoration. 389 



same species in other characters ; and these have been seized on 

 by man and much augmented — as shewn by the tail of the fan- 

 tail-pigeon, the hood of the jacobin, the beak and wattle of the 

 carrier, and so forth. The sole difference between these cases is 

 that in the one, the result is due to man's selection, whilst in 

 the other, as with humming-birds, birds of paradise, &c, it is 

 due to the selection by the females of the more beautiful males. 



I will mention only one other bird, remarkable from the ex- 

 treme contrast in colour between the sexes, namely the famous 

 boll-bird (Chasmorhynchus niveus) of S. America, the note of 

 which can be distinguished at the distance of nearly three miles, 

 and astonishes every one when first hearing it. The male is 

 pure white, whilst the female is dusky-green ; and white is a 

 very rare colour in terrestrial species of moderate size and in- 

 offensive habits. The male, also, as described by Water ton, 

 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 offering 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. nudi- 

 collis) 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 colour. In 

 a third species (0. tricaruncidatus) the head and neck alone of 

 the male are white, the rest of the body being chesnut-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. 75 



The coloured plumage and certain other ornaments of the 

 adult males are either retained for life, or are periodically re- 

 newed during the summer and breeding-season. At this same 

 season the beak and naked skin about the head frequently 

 change colour, as with some herons, ibises, gulls, one of the 

 bell-birds just noticed, &c. In the white ibis, the cheeks, the 

 inflatable skin of the throat, and the basal portion of the beak 

 then become crimson. 713 In one of the rails, Gallicrex cristatus, a 



" Mr. Sclater, ' Intellectual Ob- plate, in the ' Ibis,' 1865, p. 90. 

 server,' Jan. 1867. ' Waterloo's 76 'Land and Water,' 1867, p 



Wanderings,' p. 118. See also Mr. 394. 

 Salrin's interesting paper, with a 



