All crocodilians are great, ungainly reptiles, having broad, depressed bodies, short legs, and long, powerful, and wonderfully flexible tails which are compressed--that is, flattened sideways. Upon the upper surface of the tail lie two jagged or saw-toothed crests, which unite near the middle of the appendage, continuing in a single row to the extremity. All have thick necks and bodies protected by regular transverse rows of long, horny plates or shields, which are elevated in the center into keel-shaped ridges, forming an armor that is quite bullet-proof. The throat, the under side of the neck, and belly are not thus protected, and it is at these places, as well as at the eyes, and also just behind the ears, that the hunter directs his aim. The principal points of difference between a gavial and a crocodile are these: the former has very long, slender jaws, set with twenty-seven teeth in each side of the upper jaw and with twenty-five teeth in the under, while at the extremity of the snout there are two holes, through which pass upward the lower large front teeth, but all the remaining teeth are free, and slant well outward; whereas a crocodile has a head that is triangular, the snout being the apex; a narrow muzzle, and canine teeth in the lower jaw, which pass freely upward in the notches in the side of the upper jaw. An alligator has a broad, flat muzzle, and the canine teeth of the lower jaw fit into sockets in the under surface of the upper jaw. It is strictly an American form of the family. Its feet being much less webbed, its habits are also less perfectly aquatic, and, preferring still or stagnant fresh-water courses or swamps, it is rarely found in tide-water streams. The crocodile, on the contrary, is commonly found in swift-running, fresh and salt water rivers. He is a sagacious brute, and ferocious, often attacking human beings without provocation; but the alligator, as a rule, is not disposed to fight, although in South America, where it goes by the name of _caiman_ or _cayman_, it grows to an enormous size, and is said to be fully as dangerous as the crocodile. There is also a variety of the family--that is, a true crocodile--found in Florida, but it is very rare, and smaller than its Asiatic relative. The mouths of all these reptiles, which are large and extend beyond the ears, present a formidable array of sharp, conical teeth of different sizes, set far apart in the crocodile and the alligator, some being enlarged into tusks. All are implanted in separate sockets, and form a single row upon each jaw. When a tooth is shed or broken, a new one promptly comes up beneath the hollow base of the old one; and in this way, all ready for the need, sometimes three or four waiting teeth, packed together like a nest of thimbles, may be seen in the jaw of a dead alligator. [Illustration: YOUNG PET ALLIGATOR. From photograph by E. L. Russell, Palm Beach.]