Page:First course in biology (IA firstcourseinbio00bailrich).pdf/396

 like the leaves of trees, are delicate structures and lose perfect condition with age. Hence the annual renewal of the feathers is an advantage. Most birds shed twice a year, and with many the summer plumage is brighter colored than the winter plumage. When a feather is shed on one side, the corresponding feather on the other side is always shed with it. (What need for this?) A large oil gland is easily found on the dorsal side of the tail. How does the bird apply the oil to the feathers?

1, false quills (on thumb); 2, primaries; 3, secondaries; tertiaries (dark) are one above another at right; a, b, coverts.

A, point dividing primaries from secondaries; B, coverts.

, with regions of body marked.

S, forehead; Sc, crown (with crest); Hh, nape; K, throat; Br, breast; Ba, lower parts; R, back; Rt, tail; B, tail coverts; P, shoulder feathers (scapulars); T, wing coverts; HS, primaries; AS, secondaries; Al, thumb feathers.

In describing and classifying birds, it is necessary to know the names of the various external regions of the body and plumage. These may be learned by studying Figs. 295, 296, 297, 298. The quills on the hand