28a THE HARMONIES OP NATURE. 



at once judge of a bird's powers of flight. Thus in the ostrich 

 and cassowary, whose wings are incapable of raising them into 

 the air, the keel, or osseous crest which in most birds arises 

 from the centre of the breastbone, and serves to increase the 

 surface of muscular attachment is absent, while it projects 

 enormously in the diurnal birds of prey, in the swallows, and in 

 the hummingbirds. 



To assist the action of the wings, they are provided with a 

 crest of quill-feathers, more or less elongated, and decked with 

 6 coverts ' imbricating over each other like the tiles of a roof. 

 When expanded, these feathers press like a light fan upon the 

 elastic air-wave beneath, and considerably increase the surface 

 of the bird without materially adding to his weight. Not only 

 the size, but also the form 'and texture, of the quill-feathers has 

 a material effect on the powers of flight. Thus in the falcons, 

 each primary quill-feather is elongated, narrow, and gradually 

 tapers to a point ; the webs are entire, and the barbs closely and 

 firmly connected together. In the owls, the plumage is loose 

 and soft, and the outer edge of the primaries is serrated ; so that 

 while they are debarred from a rapid flight, which would be 

 dangerous in the gloom in which they go abroad, they are 

 enabled by the same mechanism to wing their way without 

 noise, and steal unheard upon their prey. In the ostrich, the 

 barbs of the quill-feathers have so little adhesion to each other, 

 that the air can pass readily between them, and thus the wings, 

 even by their most energetic action, are totally incapable of 

 raising the bird from the ground. Their flapping, however, 

 materially assists the action of the legs, and serves to increase 

 the speed of the giant bird when, flying over the arid plain, he 

 ' scorns the horse and his rider.' 



The penguin is totally deprived of quill-feathers, like the 

 cassowary or the kiwi ; but, though incapable of flight, this strange 

 bird makes use of its small featherless wing-stumps as excellent 

 paddles in the water, and on land as forefeet, with whose help 

 it scales so rapidly the grass-grown cliffs, as to be easily mis- 

 taken for a quadruped. Wherever great powers of flight have 

 been given, they constantly correspond with some peculiar 

 want. The food of the oceanic birds is to be sought for at a 

 great distance from land ; their prey, which consists entirely of 

 marine animals, is constantly shifting its quarters, and it is 



