The other general characters of the crocodiles and alligators consist in their long flat heads, thick neck and bodies, protected by regular transverse rows of square bony plates or shields, elevated in the centre into keel-shaped ridges, and disposed, on the back of the neck, into groups of different forms and numbers, according to the species. The mouth is extremelylarge, extending considerably behind the eyes, and furnished in each jaw with a single row of conical teeth, all of different sizes, and standing apart from one another : these are hollow within, and never vary in number, but are successively pushed out and replaced by others of larger dimensions, as the animals increase in age and size. The tongue is short and fleshy, and attaches to the under jaw throughout its whole extent. It is consequently incapable of protrusion, and from its small size and backward position seldom seen even when the animal opens its mouth, which circumstance occasioned the belief so universally prevalent among the ancients, that the croco dile was altogether deprived of this organ. The eyes are placed on the upper surface of the skull, are much approximated towards one another, and provided each with three distinct lids : the nostrils form a long narrow canal, placed at the extremity of the muzzle ; the ears are closed externally by two fleshy valves, and beneath the throat are two small pouches or glands, which open externally and contain a musky substance. Finally, the feet are provided with five toes before, long and separate, and four behind, more or less perfectly united by membranes : of these, the three interior alone on each foot are pro vided with claws, so that the two outer toes on the fore-feet, and one on the hind, are constantly clawless.
Habits of the Alligator.—It is reported by Pliny, that the Egyptian crocodile retires to a secret cave or hiding-place, on the approach of winter, and spends three or four of the coldest months in a state of lethargy, and without taking any food : this phenomenon, usually called hybernation, is almost universal among reptiles and serpents, at least in temperate and high latitudes, and has been repeatedly observed with regard to the alligators. On the approach of the cold season these animals bury themselves in the mud at the bottom of some stagnant pond, where they remain concealed and inactive till the return of spring. Travellers assure us that they are never to be found in running streams, but that they frequent in preference some stagnant pond or the creeks of large rivers. Here they may be seen in almost countless multitudes, for they are extremely numerous in the remote unfrequented parts of South America, protruding their Large flat heads through the leaves of the Nymphcca, Poutederia, and other aquatic plants which cover the surface of the water, and watching for prey ; or sometimes basking in the sun or sleeping on the banks. They never come on shore, except during the hottest
part of the day, and always retire to the water on the approach of night, during which time they are extremely active in search of prey. Their food consists principally of fish, and it is conjectured by some physiologists, that the musky fluid, secreted by the glands under the throat, acts as a kind of bait to attract their prey. The alligators are seldom known to attack the human species, unless in defence of their eggs or young; the females of these reptiles are reported to exhibit a much stronger degree of maternal affection for their offspring than usually belongs to their class. They generally lay from fifty to sixty eggs in one place, of about the same size as those of a goose, which they cover up with sand, and leave to be hatched by the heat of the sun ; never however removing to any great distance. When the young ones come forth, they are about five or six inches long, and are immediately conducted to the water by the female alligator. Seldom more than half the entire brood live to reach the water. Many aro destroyed while in the egg. The vultures waylay and watch the female alligator when she goes ashore to deposit her eggs, which they scratch up and devour as soon as she retires. Numbers of them also fall a prey to the grown males of their own species, and to various descriptions of ravenous fishes which greedily devour them. The Indiana eat the flesh of the alligators, notwithstanding its strong musky flavour ; and even Euro peans, who have succeeded in overcoming their prejudices so far as to partake of it, report it to be both delicate and savoury. A single peculiarity of habit seems to distinguish the alligators from the real crocodiles : the former never leave the fresh water, whilst the latter are known to frequent the mouths of large rivers, and even to pass between different islands, at considerable distances from one another ; and so perfectly is this characteristic of the two sub-genera, that the crocodile of the West India Islands differs from all the other American species, and exhibits only those modifications which properly belong to those of the Old World.
It was only et the commencement of the present century that the different species of alligators were properly distinguished from oue another, or even that they were suspected to be specifically different from the crocodile of the Nile. This distinction is entirely due to the late Baron Cuvier, and since the publication of the first edition of his work ' Sur les Ossemens Fossiles ' little further addition has been made to the subject. He enumerates three species, which he has definitely characterised ; and describes a fourth, which he suspects to be distinct, but of which he did not at that time possess a sufficient number of specimens to enable him to determine the question.