Turtles are four-legged reptiles, with short, stout, oval-shaped bodies encased in bony boxes, from which they are able to protrude their heads, legs and tails, and into which they can withdraw them, at pleasure. Considerable diversity exists in the size and shape of the box-like covering in the different species. The Box Tortoise can retire into his shell or house, closing the under part or plastron into a groove of the upper edge of the carapace, as the upper part is called, thus constituting for his security an impregnable retreat. There are species only partly enclosed by the shell, which cannot bring their heads and feet under cover. With his house upon his back the turtle wanders about as the snail does, and against his enemies can close its doors and be emphatically not at home. He has acute sight and hearing, but is devoid of teeth, the jaws being, like those of birds, simply cased in horn. Turtles are not altogether silent creatures, for many of them are capable of producing very loud sounds. Their eggs, which have a parchment-like covering, are buried in earth or sand, and left to themselves to hatch. The sea-turtle, our largest variety, is sometimes found to lay as many as two hundred eggs in a heap, and in tropical regions has been known to attain a weight of a thousand pounds. Even on the Atlantic Coast of the United States individuals, weighing upwards of eight hundred pounds, have not infrequently been captured. In the four species of sea-turtles, the feet are flat and paddle-shaped, and the shell of one rather leathery than horny. Some of these marine forms are carnivorous, living on fish, mollusks and crustaceans, while others are strictly vegetarians, subsisting only on roots and the various sea-weeds. The flesh of some is rich and delicious, and a favorite and costly article of food, but of others it is coarse and ill-flavored, and necessarily not edible. The eggs, however, are always sweet, good and wholesome food. Valuable articles of commerce, such as boxes, cases, knife-handles, jewelry and other delicate ornaments, are made from the shell, for it is susceptible of a very high polish, which brings out with surprising clearness its rich brown and golden shades and markings. Next to the sea-living turtles, come the fresh-water species, which eat both animal and vegetable foods. They enjoy much better than aught else a bed of soft mud, their heads lifted above the surface of the stagnant water, their long necks moving snake-like as they gulp in mouthful after mouthful of air. They are generally gregarious in habits, large numbers often being found huddled together in the sun on logs or banks, close to the water, into which they quickly slide upon the first intimation of danger. Timid as they are, yet they will snap and bite most furiously when taken in the hand.