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FORM AND HABIT: THE WING. 23 me take jou 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 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 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 Amei'ica, 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- fonnance 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