These enormous animals closely resemble seals, both in the shape of their body and the structure of their limbs, but are distinguished by the shape of their head, and by the enormous tusks which project from their upper jaw. These remarkable weapons sometimes measure two feet in length, and are of proportionate thickness. The great size of the bones of the face required for holding these teeth renders their appearance peculiarly striking, their nostrils being pushed so far upwards that, instead of being situated at the extremity of the snout, they are placed near the top of the head. Their food seems to consist of sea-weed (which they detach from the soil by means of these tusks, which act like garden rakes), as well as of animal substances. They frequently measure from twenty to twenty-five feet in length, and a full-sized Bull Walrus, weighing three thousand pounds, will yield six hundred pounds of blubber, from which excellent oil is procured. Its hide is used for harness, shoe soles, and the rigging of ships, as well as for the manufacture of glue. CHIEROPTERA—ANIMALS WITH WINGED-HANDS. FOR a long time these curious little animals puzzled the Naturalists. Aristotle defined them as Birds with wings of skin. After him, Pliny and other Naturalists fell into the same error of classifying them with the Birds; but after many centuries the different characters that fix the rank of these animals in the scale of created beings are well known, and they are placed where they belong, in the great family of Mammals, and classed as the Cheiroptera, or animals with winged-hands—as the word Cheiroptera comes from two Greek words meaning wing and hand. All the fingers of the hand (with the exception of the thumb, which is short, has a nail, and is quite free) are immoderately long, and united by means of a transparent membrane which is without hair. This membrane covers also the arm and forearm, and is simply a prolongation of the skin of the flanks, composed of two very thin layers. It also extends down the hind legs, where it is more or less developed, according to the species; but it never reaches the toes of the feet, which are short and have nails. It is owing to this membranous sail that Bats direct their course through the air in the same manner as Birds. When they are at rest they fold their wings around them, covering their bodies as if in a mantle, similar to our closing an umbrella to diminish its volume when it is no longer required. This comparison is still more exact when we note that the curiously long fingers of the animal perfectly correspond to the ribs or rods of the umbrella.