The birds belonging to this extensive order are all aquatic, and almost exclusively subsist on fishes, which they capture by diving. In conformity with this mode of life, they all present a general type of structure which is unmistakable. Their bodies are powerfully built, almost cylindrical in shape, and their legs placed far backwards. Their wings are short, feeble, and pointed, but little adapted to flight, and in many cases almost resembling fins, while their dense smooth plumage, which is impenetrable to water, admirably fits them for a residence in that element. Their beak is strong, hard, acutely pointed, and generally compressed at the sides; it is seldom much longer than the head, and its margins are usually sharp and well adapted for cutting. The foot is furnished either with three or four toes, of which the three in front are either strongly-webbed or furnished with lateral expansions of the skin, which render them efficient instruments of propulsion. The tail is often altogether wanting, or if present is always short, rounded, and generally formed of more than twelve feathers. There is much similarity in the coloration of their plumage, in which black and pure white predominate; in some species, however, variety of colour is not wanting. Generally speaking, these birds are all inhabitants of the sea; nevertheless, a few are to be met with only in inland lakes: some species have a very wide range in a great variety of climates; but the majority prefer the polar regions of the world, both north and south, from which, however, some of them migrate at stated intervals. The greater part of their lives is passed upon the surface of the water; indeed, it is only during the breeding season that they come upon dry land. Although many species fly with tolerable facility, in most instances the wings are too feeble to support the weight of their bodies, and are principally used almost like fins, to enable them to progress more rapidly when diving beneath the surface of the water, where they obtain the fishes and small crustaceans that constitute their usual food. A few diving birds build their nests solitarily; but by far the greater number congregate in innumerable hosts, and breed in company with each other upon rocks and islands that rise abruptly from the sea. The eggs are two in number.
The GREBES (Podicipites) are only to be met with in fresh water, and accordingly are classed by some naturalists in the immediate vicinity of the Coots, to which, as far as relates to the structure of their feet, they certainly bear a considerable resemblance. Their true position, however, we consider to be undoubtedly among the Divers. Their body is remarkably broad and squat; their neck long and moderately slender; their head small and elongated; their beak long, conical, and compressed at the sides, with incurved, sharp cutting edges, the lower mandible being slightly overlapped by the upper one. The legs are placed so far backward, that they seem to be attached quite to the posterior extremity of the body, and moreover are of very peculiar conformation. The tarsi are of moderate height, and so much compressed at the sides that the front of the instep presents a sharp smooth edge. The structure of the foot is likewise remarkable; of the three front toes, the exterior is as long or longer than the middle toe, while the inner toe is by far the shortest of the three; the hinder toe, which is slightly elevated, is a mere rudiment. The three front toes are connected by a web as far as the first joint, but beyond this point they are separated, although each is furnished on both sides with a broad fold of skin, which is not scalloped, but smoothly rounded off in front, where it is further strengthened by the broad flattened claws. The wings are small, short, and narrow, the second and
