work consists in forcing into its pores a solution of corrosive sublimate. The only objection to this method is its great cost. Quatrefages, however, asserts that one twenty-millionth part of corrosive sublimate is enough to destroy all the young Ship-worms in two hours. He, therefore, proposes that ships should be cleared of this fearful pest by being taken into a closed dock, into which a few handfuls of corrosive sublimate should be thrown and well mixed with the water. The salts of copper and lead have a similar effect, but do not act so instantaneously.
The Teredo does not perforate rock, but the Pholas acts an important part in bringing about geological changes, owing to his habit of boring rocks. There is no doubt that the chalk-cliffs of England are first tunnelled by the Pholades, and then gradually destroyed by the waves of the sea.
Of the Date-shell, another very interesting borer, Wood gives the following account: "It is truly a wonderful little shell. Some of the hardest stones and stoutest shells are found pierced by hundreds of these curious beings, which seem to have one prevailing instinct, namely, to bore their way through every thing. Onward, ever onward, seems to be the law of their existence, and most thoroughly do they carry it out. They care little for obstacles, and, if one of their own kind happens to cross their path, they quietly proceed with their work, and drive their tunnel completely through the body of their companion."
Of the Saxicava rugosa, another borer, Wood gives this description: "It is a flattish bivalve, symmetrical in shape when young, but oblong when old. It burrows as rapidly as the Lithodomus, and into rock of adamantine density. Sometimes it bores into corals, frequently into limestone, and often into shells, which it penetrates as deeply as the Date-shell. Some of the enormous stones employed in building the Plymouth Breakwater are now much wasted by the holes made in them by the Saxicava." Like the Date-shell, too, this animal runs its tunnels at every angle, and turns out of its course for no consideration whatever.
The Razor-shell makes a burrow in the sand, and there lives with its siphon, or recurved food-tube, appearing just above the mouth of the burrow. It may often be seen "spouting," or sending forth small jets of water from its hiding-place in the sand after the tide has retreated. On examining the spot cautiously—for the creature is somewhat shy—two round holes in the sand, answering to the two fringed openings of the Razor-shell's siphon, will be seen, resembling a key-hole, and each large enough to admit a common goose-quill. But, if the animal be approached rudely, or if the finger be placed on the openings, the mollusk disappears deep in the burrow. The Razor-shell is possessed of a very muscular "foot," as it is called, but it might as well be named a hand or a tongue. By means of this organ, which they
