Ordinary swimmers are constantly falling a prey to the sharks of warm climates. Thus Sir Brooke Watson, when in the West Indies, as a youth, was swimming at a little distance from a ship, when he saw a shark making towards him. Struck with terror at its approach, he immediately cried out for assistance. A rope was instantly thrown, but, even while the men were in the act of drawing him up the ship's side, the monster darted after him, and at a single snap took off his leg. Fortunately for the friends of sea-bathing on our shores, the white shark, like his relation, the monstrous Hammer-headed Zygæna, appears but seldom in the colder latitudes, though both have occasionally been found on the British coast. [Illustration: Picked Dog-Fish.] The northern ocean has got its peculiar sharks, but they are generally either good-natured like the huge basking shark (_S. maximus_), which feeds on sea-weeds and medusæ, or else like the _Picked_ dog-fish (_Galeus acanthius_), of too small a size to be dangerous to man, in spite of the ferocity of their nature. [Illustration: Blue Shark.] But the dog-fish and several other species of our seas, such as the Blue Shark (_Carcharias glaucus_), though they do not attempt the fisherman's life, are extremely troublesome and injurious to him, by hovering about his boat and cutting the hooks from the lines in rapid succession. This, indeed, often leads to their own destruction, but when their teeth do not deliver them from their difficulty, the blue sharks, which hover about the Cornish coast during the pilchard season, have a singular method of proceeding, which is, by rolling the body round so as to twine the line about them throughout its whole length; and sometimes this is done in such a complicated manner, that Mr. Yarrell has known a fisherman give up any attempt to unroll it as a hopeless task. To the pilchard drift-net this shark is a still more dangerous enemy, and it is common for it to pass in succession along the whole length of net, cutting out, as with shears, the fish and the net that holds them, and swallowing both together. [Illustration: Saw-Fish.] [Illustration: Sword-Fish.] The Saw-snouted Shark or Saw-fish (_Squalus pristis_), which grows to fifteen feet in length, and the Sword-fish (_Xiphias gladius_, _platypterus_), are furnished with peculiarly formidable weapons. The long flat snout of the former is set with teeth on both sides through its whole length, while the upper jaw of the latter terminates in a long sword-shaped snout. A twenty-feet long sword-fish once ran his sword with such violence into the keel of an East Indiaman, that it penetrated up to the root, and the fish itself was killed by the violence of the shock. The perforated beam, with the driven-in sword, are both preserved in the British Museum, and give a good idea of the prodigious power of the leviathans of ocean. [Illustration: Torpedo.]