ORNITHOLOGY 707 er with mammals through the ornithorhynchus and the ostrich. Though these affinities can- not be made the basis of a natural classifi- cation, they are interesting, ingenious, and to some extent philosophical. Oken, in various works from 1809 to 1843, published his system of classification, in which birds are called ear animals, in the division according to the senses, because in them for the first time the external auditory meatus as well as the cochlea is ex- hibited in perfection ; birds are also nerve ani- mals, in the anatomical division, as they have a complete nervous system with cerebrum and cerebellum. They belong to his 2d province, of sarcozoa, 4th circle or flesh animals, and 12th class or otozoa or neurozoa. They are the first encephalic animals, as the brain defines the head, which is here for the first time freed from the trunk and placed upon a long neck far removed from the thorax, hence also called cervical animals ; the caudal vertebrae, on the contrary, are fewer than in other classes. Birds are capable of instruction, affection, imitation, gratitude, and other mental manifestations not seen in reptiles and fishes. They are the closest repetition of insects, the thorax predominating over the rest of the body, with large respirato- ry muscles ; their lungs are a cluster of insect tracheae, full of foramina through which air penetrates all over the body, as in insects ; the intestine lies in the air, and the bird to a cer- tain extent breathes from it; the whole bird is lung, and its body a thoracic cavity, as the latter is a sexual cavity in the fish and an abdominal cavity in the reptile; the food is crushed in a muscular stomach, as in insects ; a bird is an insect with fleshy limbs, and a feather is an insect's wing. With the bird, for the first time, the voice proper breaks forth ; "the bird speaketh the language of nature." In Oken's " Physiophilosophy " (Ray society edition, London, 1847) are given two great di- visions of birds, according as the young require to be fed by the parents or not, the former be- ing the lowest ; this principle of division, first published in 1821, has retained its place in or- nithological science, and lies at the base of the systems now generally followed in Europe and in this country. Carus (1828), in his Grund- riss der vergleicTienden Anatomie, ranks birds in his 6th class or cephalo-thoracozoa, charac- terized by great development of the respirato- ry organs. He makes the orders : I., natantes, having relations with reptiles, especially such of its members as fly poorly or not at all (like the penguins) ; II., vadentes or waders; III., prendentes, with the suborders rapaces, pas- seres, scansores, and gallince; and IV., incedentcs or struthious birds, having relations to mam- mals. Ehrenberg (1836) ranks birds as the sec- ond and last class of the nutrientia or animals which take care of their young ; this division is not strictly natural, as some reptiles and fishes have a care for their progeny. The eggs of birds have generally been selected for inves- tigations of embryology. The unity of anatom- ical structure in all vertebrates is confirmed by the common structure of the primitive egg, and the order of classification from anatomical evi- dence by the metamorphoses which each class undergoes to its full development. The bird goes through its fish-like and reptilian structure and form ; the only difference between the egg of a bird and a mammalian ovum, as to exter- nal covering, is that the former has a hard shell when laid protecting the immature chick, while in the latter the envelopes remain mem- branous, having a peculiar connection with the maternal body which is not severed until the birth of the young. Von Baer (1828) places birds in his double symmetrical type, whose embryos acquire an allantois, but have no um- bilical cord, having wings and air sacs. Van Beneden (1855) ranks birds as the second class of his hypocotyledones or hypovitellians, in which the vitellus enters the body from the ventral side. Prof. Agassiz ("Lecture on Em- bryology," Boston, 1849) gives the results of some observations on the structure of the bird embryo, from which it appears that the limbs are not at first developed in the form which is to be permanent ; the legs and wings are formed as fins ; in all the orders of birds, with their various powers of locomotion, the legs and wings are uniformly webbed like the fins of fishes ; in the same manner the primary con- dition of the heart, lungs, and other organs of a bird is that of these organs in a fish. This would indicate that the web-footed birds are lower in the scale than those with divided toes ; and that the union of all the former into one group, however different the structure of their wings, plumage, and internal organs, and their mode of life the almost wingless penguin with the swift-flying ocean birds, the hook- beaked predaceous gulls with the flat-billed and timorous ducks must be an unnatural ar- rangement. The examination of the feet of an embryo robin, swallow, warbler, and finch, showed all four toes directed forward and webbed, while in the mature birds they are separate, three directed forward and one back- ward ; he found the bill of the immature robin resembling that of a vulturine bird, indicating the comparatively low type of the latter ; in- deed some water birds, like lestris (skua gull), have a bill very greatly resembling that of the vultures ; some birds of prey also resemble wa- ter birds in the rudiment of a web between the toes. He regards birds which have all their toes directed forward as of a lower type than those in which one is directed backward, as, for instance, the pelicans and cormorants among water birds, and the swifts (genus cypselw, 111.) among swallows ; a similar idea was broach- ed by Sundevall in 1835. In Prof. Agassiz's classification ("Contributions to the Natural History of the United States," vol. i., Bos- ton, 1857), birds form the seventh class of ver- tebrates, with four orders, natatores, gralla, rasores, and insessores (including scansores and accipitres).1iQ principle of classification of
