FORM AND HABIT: THE WINQ. 23 



me take you tinally to the poultry yard, wliere in the 

 waddling Duck you will see an undeniable instance of 

 degenei*ation. 



As the seat of sexual characters the wing is some- 

 times most singularly developed or adorned. The males 

 of the Argus Pheasant and Pennant-winged Nightjar 

 have certain feathers enormously lengthened ; the Stand- 

 ard-bearer has white plumes growing from the wing ; and 

 there are many other cases in which the wing presents sex- 

 ual characters, not alone through display, but also by 

 use as a musical organ. I do not refer to the whistling 

 sound made by the wings of flying Doves or Ducks, or 

 the humming of Hummingbirds, but to sounds volun- 

 tarily produced by birds, and e^-idently designed to an- 

 swer the purpose of song. 



A simple form of this kind of " music " is shown by 

 the cock in clajjping his wings before crowing, in the 

 " drumming " of Grouse, or in the " booming " of Night- 

 hawks, as with wings set they dive from a height earth- 

 ward. The male Cassique {Ostinops) of South America, 

 after giving voice to notes which sound like those pro- 

 duced by chafing trees in a gale, leans far forward, 

 spreads and raises his large orange and black tail, then 

 vigorously claps his wings together over his back, mak- 

 ing a noise which so resembles the cracking of branches 

 that one imagines the birds learned this singular per- 

 formance during a gale. 



The birds mentioned thus far have no especial wing 

 structure beyond rather stiffened feathers ; but in the 

 "Woodcock, some Paradise-birds and Flycatchers, Guans, 

 Pipras, and other tropical l)irds, certain wing-feathers 

 are singularly modified as musical instruments. Some- 

 times the outer primaries are so narrowed that little but 

 the shaft or midrib is left, as in both sexes of the Wood- 

 cock, when the rapid wing-strokes are accompanied by a 



