Section III.—Aquatic Mammalia, having no Hind Limbs, and the Fore Limbs converted into Fins.
XI. Cetacea, or sea mammalia, the principal of which are the whale family, the dolphin family, the manati, the porpoise family, and the narwhal, or sea-unicorn.
THE AVES, OR BIRDS,
Lay eggs from which their young are hatched by what is called incubation. Their skins are covered with feathers; and their jaws are horny, without teeth. Their blood is warm, and circulates like that of the mammalia. The six orders of Aves are as follow:—
1. Raptores, or birds of prey. These birds are distinguished by a very strong and sharp bill more or less curved, but always hooked at the extremity of the upper mandible, which is covered at the base with a kind of skin called the cere. The nostrils are usually open. The legs are very strong, the feet are large, and the toes, which are four in number, are armed with very strong, sharp, curved claws. The principal raptorial birds are the vultures, including the condor; the falcon family, including the eagles, hawks, kites, and buzzards; and the owls.
2. Insessores, or perching birds. These birds have all feet formed for perching, the hind toe springing from the same place as the other toes, which gives them great power of grasping. Their legs are of moderate length, and their claws not sharply curved. This order includes the thrushes, nightingales, and all the finest songsters of our groves, with the robin-redbreast, the sparrow, and other birds seen about dwellings, the swallows, the larks, the crow family, the kingfishers, the birds of paradise, and the humming birds.
3. Scansores, or climbers. These birds have two toes before and two behind. This construction gives them such great power of climbing, that they can ascend the perpendicular trunk of a tree. The principal birds in this order are the parrots, the cuckoos, and the woodpeckers.
4. Rasores, or gallinaceous birds. These birds have the head small in proportion to the body. The bill is generally short, with the upper mandible somewhat curved. The nostrils have usually a protecting fleshy membrane. The tarsus, or lower part of the leg, is long and bare, and there are four toes, those in front being united by a slight membrane, while that behind is generally higher up the leg, and smaller than the others. This order comprises most of the birds used as food, and includes the peacock, the turkey, the common cock and hen, the partridge, the pheasant, and the pigeon family.
5. Grallatores, or Waders. These birds are characterised by their long and slender legs, and by the thighs being more or less bare. There are three anterior toes, more or less united at the base by a membrane, or rudimentary web. The hind toe is wanting in some members of the order. This order contains the ostrich family, the bustards and plovers; the cranes, herons, and storks; and the snipes and woodcocks.
6. Palmipedes, or web-footed birds. These birds have the legs and feet short, and placed behind, with their fore toes united by a thick and strong membrane. The neck is much longer than the legs, and their bodies are covered with a dense layer of down beneath the outer plumage, which is close, and imbued with an oily fluid that repels the water. The principal birds in this order are the grebes, the auks and penguins, the petrels, the pelican and cormorant and the swans, ducks, and geese.