A =feather grows= from a small projection (or papilla) found at the bottom of a depression of the skin. The quill is formed by being moulded around the papilla. Do you see any opening at the tip of the quill for blood vessels to enter and nourish the feather? What is in the quill? (Fig. 291.) The rachis? A young contour or quill feather is inclosed in a delicate sheath which is cast off when the feather has been formed. Have you seen the sheath incasing a young feather in a moulting bird? There are considerable =areas= or tracts on a bird’s skin =without contour feathers=. Such bare tracts are found along the ridge of the breast and on the sides of the neck. However, the contour feathers lie so as to overlap and cover the whole body perfectly (Fig. 294). [Illustration: FIG. 295.—WING OF BIRD. _1_, false quills (on thumb); _2_, primaries; _3_, secondaries; tertiaries (dark) are one above another at right; _a_, _b_, coverts. ] The shedding of the feathers is called =moulting=. Feathers, 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 coloured 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? [Illustration: FIG. 296. _A_, point dividing primaries from secondaries; _B_, coverts. ] [Illustration: FIG. 297.—CEDAR WAXWING, 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 are called primaries, those on the forearm are the secondaries, those on the upper arm are the tertiaries. Those on the tail are called the _tail quills_. The feathers at the base of the quills are called the _coverts_. The thumb bears one or more quills called the spurious quills. Is the wing concave on the lower or the upper side? Of what advantage is this when the bird is at rest? When it is flying? [Illustration: FIG. 298.—PLAN OF BIRD. _s_, centre of gravity. ] [Illustration: FIG. 299.—POSITION OF LIMBS OF PIGEON. ]