FORM AND HABIT: THE WING. 23 
me take you finally to the poultry yard, where in the 
waddling Duck you will see an undeniable instance of 
degeneration. 
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 yolun- 
tarily produced by birds, and evidently designed to an- 
swer the purpose of song. 
A simple form of this kind of “ music” is shown by 
the cock in clapping 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 birds, 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 
