The elongate cylindrical body, generally terminating in a more or less pointed snout, and passing into a powerful and flexible tail, blade-like at its extremity, gives to the Sharks a most extraordinary power of swimming, with regard to endurance as well as rapidity of motion. Many, especially the larger kinds, inhabit the open ocean, following ships for weeks, or pursuing shoals of fishes in their periodical migrations. Other large-sized sharks frequent such parts of the coast as offer them abundance of food; whilst the majority of the smaller kinds are shore fishes, rarely leaving the bottom, and sometimes congregating in immense numbers. The movements of sharks resemble in some measure those of snakes, their flexible body being bent in more than one curve when moving. Sharks are most numerous in the seas between the Tropics, and become scarcer beyond, a few only reaching the Arctic circle; it is not known how far they advance southwards towards the Antarctic region. Some species enter fresh waters, and ascend large rivers, like the Tigris or Ganges, to a considerable distance. The pelagic as well as the shore species have a wide geographical range. Very few descend to a considerable depth, probably not exceeding 500 fathoms. There are about 140 different species known. Sharks have no scales like those of other fishes; their integuments are covered with calcified papillæ which, under the microscope, show a structure similar to that of teeth. If the papillæ are small, pointed, and close set, the skin is called “shagreen;” rarely they are larger, appearing as bucklers or spines, of various sizes. These fishes are exclusively carnivorous, and those armed with powerful cutting teeth are the most formidable tyrants of the ocean. They have been known to divide the body of a man in two at one bite, as if by the sweep of a sword. Some of the largest sharks, however, which are provided with very small teeth, are almost harmless, feeding on small fishes only or marine invertebrates. Others, particularly of the smaller kinds, commonly called “Dog-fishes,” have short or obtuse teeth, and feed on shells or any other animal substance. Sharks scent their food from a distance, being readily attracted by the smell of blood or decomposing bodies.