374 The Descent of Man. Tart II. 



bare white quills surmounted by dark-blue plumes, which it can 

 elevate into a great dome no less than five inches in diameter, 

 covering the whole head. This bird has on its neck a long, thin, 

 cylindrical fleshy appendage, which is thickly clothed with scale- 

 like blue feathers. It probably serves in part as an ornament, 

 but likewise as a resounding apparatus; for Mr. Bates found 

 that it is connected " with an unusual development of the 

 " trachea and vocal organs." It is dilated when the bird utters its 

 singularly deep, loud and long sustained fluty note. The head- 

 crest and neck-appendage are rudimentary in the female. 44 



The vocal organs of various web-footed and wading birds are 

 extraordinarily complex, and differ to a certain extent in the two 

 sexes. In some cases the trachea is convoluted, like a French 

 horn, and is deeply embedded in the sternum. In the wild 

 swan (Cy gnus ferns) it is more deeply embedded in the adult male, 

 than in the adult female or young male. In the male Merganser 

 the enlarged portion of the trachea is furnished with an additional 

 pair of muscles. 45 In one of the ducks, however, namely Anus 

 punctata, the bony enlargement is only a little more developed 

 in the male than in the female. 46 But the meaning of these 

 differences in the trachea of the two sexes of the Anatidse is not 

 understood ; for the male is not always the more vociferous ; 

 thus with the common duck, the male hisses, whilst the female 

 utters a loud quack. 47 In both sexes of one of the cranes (Grus 

 viryo) the trachea penetrates the sternum, but presents " certain 

 " sexual modifications." In the male of the black stork there is 

 also a well-marked sexual difference in the length and curvature 

 of the bronchi. 48 Highly important structures have, therefore, in 

 these cases been modified according to sex. 



It is often difficult to conjecture whether the many strange 

 cries and notes uttered by male birds during the breeding- 

 season, serve as a charm or merely as a call to the female. The 

 soft cooing of the turtle-dove and of many pigeons, it may be 

 presumed, pleases the female. When the female of the wild 



44 Bates, ' The Naturalist on the of eight, and yet this bird (Jerdon, 

 Amazons,' 1863, vol. ii. p. 284 ; ' Birds of India,' vol. iii. p. 7(33) is 

 Wallace, in ' Proc. Zool. Soc.' 1850, mute ; but Mr. Blyth informs me 

 p. 206. A new species, with a still that the convolutions are not con- 



. larger neck-apperdage (<7. pendu- stantly present, so that perhaps 



Hger), has lately been discovered, they are now tending towards 



see ' Ibis/ vol. i. p. 457. abortion. 



45 Bishop, in Todd's ' Cyclop, of 48 ' Elements of Comp. Anat.' by 

 Anat. and Phys.' vol. iv. p. 1499. R. Wagner, Eng. translat. 1845, p. 



46 Prof. Newton, 'Proc. Zoolog. 111. With respect to the swan, as 

 Soc' 1871, p. 651. given above, Yarrell's 'Hist, of 



47 The spoonbill (Plataka) has British Birds,' 2nd edit. 1845, voL 

 U trachea convoluted into a figure iii. p. 193. 



