404 A HISTORY OF BIRDS 



middle of the trachea considerably enlarged to form a long, 

 fusiform swelling, while in the Goosander {Mergus merganser) 

 there are in the male two such swollen areas, and one, be it 

 noted, in the female. The trachea of the male Velvet Scoter 

 (CEdemia fused) is still more remarkable. In this bird the bulb 

 at the end of the trachea is wanting, but the tube, near its lower 

 third, becomes abruptly swollen to form a large spherical 

 chamber, made up of tracheal rings fused together to form a 

 homogeneous wall, while immediately below the larynx is a 

 second chamber, this, however, being formed outside the tracheal 

 tube and with which it communicates through special apertures, 

 as may be seen in 111. 44. 



What purpose do these structures serve? If as a resonator 

 for increasing the sound of the voice then it is curious that in 

 many Ducks the female, which has no resonator, has the louder 

 voice, as in the case of the Mallard, for example. Ducks with 

 precisely similar resonators have absolutely different calls. The 

 coiled tubes of the Curassows, Swans and Cranes, on the other 

 hand, certainly do seem to act directly upon the voice, producing 

 a loud trumpeting sound, yet the similarly convoluted windpipe 

 of two species of the Painted Snipe does not appear to have any 

 vocal function at all. In the Painted Snipe {Rhj/nchea), be it 

 noted, the convolutions are met with only in the females, but 

 these, as in some other species to which reference has already 

 been made, are large and more resplendent than the males, 

 which, as in all such cases, undertake the charge of the eggs 

 and young. The elaboration of these organs is, in short, 

 something of a mystery. They seem to come within the cate- 

 gory of what have been called "organs of extreme perfection," 

 since unnecessary energy seems to have been expended in 

 developing structures which appear in some cases at least to 

 serve no purpose. If indeed they be resonators, then it is more 

 remarkable that the majority of species contrive to make louder 

 sounds without the aid of such contrivances, while among birds 

 with similarly elaborated windpipes some produce a sonorous 

 kind of music, others no remarkable sound at all. 



The Passerine birds provide a parallel. Here the elaborate 

 arrangement of muscles and tracheal rings which form the 

 syrinx have resulted in the evolution of an organ of song, of 

 great perfection, as witness such performers as the Nightingale, 



