BIRD. sometimes be transformed into highly ornamen- tal plumes. The tail-feathers grow in pairs, the reason for which arrangement is shown by Ar- •chseopteryx, where each vertebra of the lizard- like tail supported one on each side. The re- ■duction of this long caudal skeleton to a pygo- ■style, and the consequent crowding of the feathers upon a short base, ssems to have pro- duced the modern fan-shaped tail. "The normal number of reetrices is 6 pairs, but a few birds possess 10 or 11: several 9, 8, or 7; many only S, and Crotophaga (anis) only 4 — the diminution being brought about by the suppression of the outer pair or pairs." The main purpose of the tail, which is capable of much movement, is to assist the bird to balance, check, and guide itself. There seems, however, to be no relation between the size and shape of the tail and the character of the wings, though its shape is pretty constant within each order. Thus most of the sea-birds, water-fowl, waders, and game-birds have short, compact, inconspicuous tails, until "we come to the pheasants, where they are likely io be exceedingly long and showy. The pigeons and their allies have broad tails, and those of the birds of prey are stout and square. The picarian families are mostly possessed of tails, -which are long, or strikingly colored, as notably in the trogons and some cuckoos, or marked with peculiarities of form as in the motmots, or are "the subject of special ornamentation as among the humming-birds. In the great tribe of Pas- seres the utmost variety exists, the magnificent lyre-bird (see Plate of Lyre-bird, etc.) coming next to the bob-tailed pittas; and here, among lhe short-tailed finches, warblers, and thrushes, are found birds capable of such caudal displays as those of the paradise-birds, sunbirds, some jays, etc. This shows that the essential service -of the tail in flight may be performed by an appendage of almost any shape, and that the •conspicuous, llexible. and somewhat imimportant nature of the organ has caused it to be influenced by natural (and especially by sexual) selection in an unusual degree as a means of displaying sexual ornamentation and emotion. This is the -explanation of the possession by male pheasants -of their magnificent trains, of the gorgeous array spread by the peacock (though here it is really the tail-corcrfs) , which he rattles nervously, as if to call attention to the show ; of the symmetri- cal beauty of the lyre-bird's tail ; and of the amazing caudal nmament-s of birds of paradise. (See Phites of Peacock.s ; Li-re-eirds : Birds of Pabadise.) "The motmot," remarks F. M. Chapman (see Motmot, for interesting details), "gesticulates with its tail in a remarkable man- ner, swinging it from side to side, so that it suggests the pendulum of a clock, or sweeping it about in circles with a movement which re- minds one of a band-master flourishing liis baton. We shall find in other species, also, that the tail, more than any other organ, is used to express emotion. Recall its twitching and wagging: how it is nervously spread or 'jetted,' showing the ■white outer feathers, as in the meadow-lark. The tail may be also expressive of disposition. Com- pare the drooped tail of a pensive fly-cat<:her ■with the uplifted member of an inquisitive wren." Crests, f.'omhs. etc. — Crests in very great va- riety, usually able to be elevated or depressed at the will of the bird, and ornamental plumes or 97 BIBD. tufts of feathers, such as the aigrets (see Aioret) of herons, and the 'tassels' hanging from the turkey's breast, are developments of the plu- mage that might properly be discussed here; but the limitations of space compel a reference in- stead to the biographies of the various birds that exhibit them. The beak and heail-appendages, such as combs, wattles, carunculated ceres, 'hel- mets,' etc., are, however, dermal growths, which require mention; as also will the coverings of the feet. The Beak. — The beak, bill, or neb of a bird is formed of two homy sheaths, overlying bony supports, and forming the mouth and food-get- ting organ of a bird. It consists of two mandi- bles, an upper and a lower, into which the fore- most bones of the skull are produced, all appear- ance of lips being lost. It is not furnished with proper teeth, although rudiments of them have been observed in the embryos of some parrots; and the marginal laminae with which the bills of many water-fowl are furnished partake of the same character, being secreted by distinct pulps. The resemblance of these marginal lami- n!e to teeth is particularly marked in the mer- ganser (q.v.). The bills of birds differ much, according to their ditt'erent habits, and particu- larly according to the kind of food on which they are destined to live, and the manner in which they are to seek it. In birds of prey, the beak is strong; the upper mandible arched or hooked, and very sharp ; the edges sharp, often notched, and the whole beak adapted for seizing animals, and tearing and cutting to pieces their flesh. A powerful, short, hooked beak, sharp- edged and notched, indicates the greatest courage and adaptation to preying on living animals. The beak of the ^^llture is longer and weaker than that of the eagle or falcon. In birds which feed on insects and vegetable substances, tlic hooked form of the beak is less common, though well marked in parrots: those birds which catch insects on the wing, such as the niglit- jars, swifts, etc., are remarkable for the deep division of the beak, and their consequently wide gape, and an analogous provision to facilitate the taking of prey is to be observed in herons, kingfishers, and other fishing birds; but the ob- ject is attained in their case by the elongation of the beak, whereas birds which catch insects on the wing have the beak -very short. Birds which feed chiefly on seeds have the beak short and strong, for bruising them : while the l)eak of insectivorous birds is comparatively slender. Many aquatic birds have broad, comparative- ly soft and sensitive bills, with lamina> on the inner margin for straining the mud from which nnich of their food is to be extracted ; other birds, as snipes, avocets, etc., seeking their food also in mud. have slender bills of remarkable sensibility. .s the varieties of form roughly distinguished the larger and more obvious of the groups of l)irds. the bill was made the stand- ard for the early classifications, giving such group-names as Dentiroslres, Conirostres,etc., no longer of scientific value. The modifications of form are very numerous, and the peculiarities of the bills of toucans, hornbills, spoonbills, crossbills, parrots, humming-birds, etc, are very interesting, and intimately connected with habits. Some of the modifications, however, are sexual and transitory, such as the knob on the beak of the pelican, and the deciduous parts of that of
