Page:The American Cyclopædia (1879) Volume II.djvu/673

 BIRDS 653 as they are climbers, waders, swimmers, perch- ers, &c. Besides their muscular integuments, all birds have horny beaks and nails, a fleshy cere at the base of the bill, and scaly coverings to the lower extremities, wherever they are bare. Their peculiar covering, found more or less perfectly in the whole class, and in no oth- er kind of animals, is their plumage. In cer- tain families, as that of the ostrich, the plu- mage makes a remarkably close approach to the hairy coverings of land mammals. In other families, such as the divers, the alcadee, the guillemots, &c., the plumage more nearly ap- proaches the furry coats of the otter and the seal. The plumage of all birds of this order is close, oily, and often glossy, and the skin is moreover covered with a thick layer of down. In the young of birds the proximate resem- blance of their plumage to the hairy covering of mammals is even more marked. The bills of birds enable the raptorial families to tear their prey into fragments ; they supply to the 1. Digestive Apparatus: c, Crop; g. Gizzard, t. Trachea. 6, 6. Bronchial Tubes. /, /. Lungs. 2. Bones of the Wing. fly-catcher, the swallow, and the whip-poor- will exquisitely contrived insect traps ; they give to the woodcock, the snipe, and other waders, the power of determining what is suit- able for food, with no other aid than the most delicately sensitive nervous membranes of their long probe-like jaws. In birds, the alimentary canal comprises an oesophagus, a crop, a mem- branous stomach, a gizzard, an intestinal canal, and a cloaca, in which the urinary ducts also terminate. The gizzard is a powerful organ in promoting digestion, especially with galli- naceous and other graminivorous birds. That peculiarity of structure, however, which most fully distinguishes this from every other class of animals, is the immediate and constant con- nection of the lungs with numerous air cells <hat permeate the entire frame, extending even throughout the bony portions. These mem- branous air cells occupy a very considerable portion both of the chest and of the abdo- men, and have the most direct and uninter- rupted communication with the lungs. The long cylindrical bones are so many air tubes. Even the flat bones are occupied by a cellular bony network, filled with air. The large bills in certain genera, even the very quill feathers when fully developed, receive more or less air from the lungs, at the pleasure of the birds. By these means the erectile crests of a number of species are alternately depressed or elevated. The design of these chains of air cells, pene- trating into every portion of the structure of birds, is obvious. Lightness of the body for motion in the air or water, or on the land, is indispensable. Hence we find in birds of the highest and most rapid flight the largest supply of air cells. This pneumatic apparatus is also supposed to assist materially in the oxidation of the venous blood, and the air contained in the cells is presumed to operate upon the blood vessels and lymphatics in contact with them. The volume of air which birds are thus enabled to introduce into their bodies, and the ease and power with which they can at will expel it, taken in connection with their peculiar organs of voice, explain how some of the smallest members of the class, as the common canary bird or the black-poll warbler of North Ameri- ca, are enabled to give utterance to such pow- erful notes, and to continue them so long with- out any apparent effort. The construction of the larynx in this class is very peculiar, bear- ing a remarkable resemblance to certain wind instruments. This organ is made up of two- parts, the true rima glottiilis, at the upper part of the windpipe, and the bronchial larynx, which is furnished with a peculiarly tense mem- brane, performing the same duty as the reed in the clarinet. The song of birds is the ex- pression of amorous desire. It is confined to the males, and in a state of nature is heard only during the breeding season. Many birds have no power of song. The call of birds, however, is common to both sexes and all species, and is their universal language. Many birds, which are mute in the countries to which they migrate in the winter months, and have the reputation of being entirely voice- less, are clamorous when they breed, as is the case with the European woodcock (scolopax rusticola), and the jacksnipe, or judcock (scolo- pax gallinula). Some birds are known by their clang of tongues in their migrations, clamoring in order to regulate their squadrons, as wild geese, cranes, and many of the waders, which rise voiceless when they are alarmed by the sportsman, and feed in the daytime silent. Others are, so far as we know, silent at all times, except when they spring upon the wing, in any sudden alarm. Some again, as the pas- senger pigeons, make their migrations in silence, take wing in silence when alarmed, yet when alone in the woods make the solitudes sono- rous; others, like rooks, are habitually noisy, especially in the breeding season, yet rise in