Fig. 1.-Parts of the Feather.
Fig. 2.-Matrix of a growing Feather, laid open.
1, 1. Capsule of the matrix. 2. 2. External membrane. 3, 3. Matter of the vane. 4. Internal membrane. 5. Bulb, or medulla.
Figs. 3 and 4.-Structure of the Bulb.
Fig. 3.-1,1,1. Bulb. 2. Part of the bulb in process of drying up as the shaft forms. 3. Part of the completed shaft. 4,4. Growing barbs.
Fig. 4.-1. The medulla or bulb. 2 2, 3 8. 4 4, 5 5. Membranous cones, indicating stages of growth of the medullary matter.
Fig. 5.-Section of the Shaft and Vane magnified.
1. The pith. 2. Horny external surface of shaft. 8. Concave internal surface. 4. Flat side of shaft. 5. 5. Bases of barbs. 6, 6. Barbules.
The plumage is generally changed several times before the bird is adult; but some of the falcons are said to assume the mature plumage after the first moult, as the Greenland and Iceland falcons.-Feathers serve to protect birds from injurious external influences, such as extremes of cold and heat, rain, etc, for which their texture and imbricated arrangement admirably adapt them; and they also furnish their principal means of locomotion, in the latter case being stronger, more compact, and longer than those which cover the body. They generally increase in size from the head backward, and have received special names according to the region of the body, which are important aids in describing and recognizing species. Some of these names, constantly used in the ornithological articles of this Cyclopte-dia, not readily understood from the words themselves, are as follows: the scapulars, above the shoulder blade and humerus, apparently on the back when the wing is closed; axillaries, long and straight feathers at the upper end of the humerus, under the wing; tibials, covering the leg; lesser wing coverts, the small feathers in rows upon the forearm; under coverts, lining the lower side of the wings; the longest quill feathers, arising from the bones of the hand, are the primaries; the secondaries arise from the outer portion of the ulna, and the tertiaries from its inner portion and the humerus; the bastard wing consists of the quills growing from the rudimentary thumb; greater wing coverts, the feathers over the quills; tail coverts, upper and under, those above and below the base of the tail feathers.
The relative size of the quills on the hand and forearm, and the consequent form of the wings, are characteristic of the families of birds, and modify essentially their powers of flight. The breadth of the wing depends principally on the length of the secondary quills, and its length on that of the primaries. Leaving out of view the proportions of the bones and the force of the muscles of the wings, when the primaries are longest at the extremity of the pinion, as in the falcons and swallows, causing an acuminate form of wing, we may know that the powers of flight are great, requiring comparatively little exertion in the bird; but when the longest primaries are in the middle of the series, giving rise to a short, broad wing, as in the partridge and grouse, the bird can fly only a short distance at a time, with great effort, and a whir well known to the sportsman. Not only the shape of the wing, but the close texture of its feathers, must be taken into account in the rapid strong flight of the falcon; the loose soft feathers of the wings in the owls, and the serrated outer edge of the primaries, while they prevent rapid flight, enable them to pounce noiselessly upon their vigilant prey.-Most birds, and especially the aquatic families, are provided with an oil gland at the base of the tail, whose unctuous secretion is distributed over the feathers by means of the bill, protecting their surface against moisture; the shedding of the water is not owing entirely to the oily covering, but also to a thin plate of air entangled by the feathers, and probably also to an actual repulsion of the particles of water by the feathers, as is seen in the leaves of many aquatic plants; the arranging of the plumes by the bill of the bird being rather to enable them to take down a large quantity of air, than to apply any repellent oily covering.-The plumage of birds has an infinite variety of colors, from the sombre tints of the raven to the pure white of the egrets, and the gorgeous hues of the lory, toucan, trogon, and humming birds; the females have generally less lively colors, and the summer livery of both sexes is often different from that of winter.
One of the most curious phenomena connected with feathers is the annual moult, and the change of color during that and the breeding season; moulting usually takes place after the young have been hatched, the whole plumage becoming dull and rough, and the bird more or less indisposed, with a temporary loss of voice in the singing species. According to Mr. Yarrell, the plumage of birds is changed by the mere alteration of the color of the feathers; by the growth of new feathers without the loss of any old ones; by the production of new feathers in the place of old ones thrown off, wholly or in part; and by the wearing off of the light tips as the breeding season approaches, exposing the brighter tints underneath. The first two of these changes occur in adults at the end of spring, the third being partial in spring and complete in autumn. Though the perfect plumage is non-vascular and epidermic, the colors change, probably by some vital process, without the loss of a feather; when the winter livery succeeding the autumnal moult begins to assume its bright characters, the new color generally commences at the part of the web nearest the body, and gradually extends to the tip.