Among the largest of all is the edible snail, which is largely used for food in many parts of Europe and is imported into the United States and pickled, to be eaten by those who like this delicacy.

Most of the gastropod mollusks, however, live in the water, some inhabiting ponds and streams, while others dwell in the sea.

In almost every brook and every ditch, for example, you may find water-snails of different kinds. Some are quite flat, and some are conical and pointed. Some are as large as land-snails, and some are so tiny that they are almost always overlooked. Most of them feed upon decaying leaves, and they have an odd way of traveling by floating upside down at the surface of the water, each with its broad fleshy "foot" expanded, so as to convert themselves into tiny boats. You may sometimes see quite a fleet of these little creatures being carried along by the stream. But if you throw a stone into the water they all sink down to the bottom at once, and do not resume their journey until many hours or even days afterward.

The eggs of this snail are laid in long jelly-like ribbons, which are generally fastened either to the stems and leaves of water-plants, or under the edges of large stones lying at the bottom of the stream. A very large number of gastropods live in the sea. One of the best known of these is the whelk, of which one reads in all books of English natural history. On almost every sandy and shingly beach, in Western Europe, one may find it lying about in hundreds; and even in large inland towns one often sees whelks for sale, both in fishmongers' shops and on barrows at the corners of the streets. Its eggs are one of the curiosities of the sea-beach—small, yellowish-white objects about the size of peas, made of tough, parchment-like skin, and fastened together in bundles about as big as cricket-balls. You may often find these bundles on the shore in dozens; and most likely you will wonder how the whelk ever managed to lay a batch of eggs a good deal bigger than itself.

But the fact is that the eggs of the whelk are just like those of the frog. When they are first laid they are very tiny; but the tough skin of which they are made is very elastic, so that it will stretch almost like a piece of india-rubber. Besides this, it has the curious property of allowing water to soak in from the outside, but not to pass out again. So as soon as the eggs are dropped into the sea they begin to swell, and before very long they are quite twenty or thirty times as large as they were when they were first laid.

We do not have these whelks in North America, but we have a variety of small gastropods, whose shells are sometimes rough and coiled in a spiral form, sometimes round like land-snails, and of various sizes. One of them is the purpura, which has many ribs, and broad dark and light stripes running spirally. The purpura of the Mediterranean is famous for the purple dye obtained from its body; but our species yields such a dye also in small quantity. This was the dye anciently known as Tyrian purple. It is contained in a little bag behind the throat, which holds just one small drop of liquid, and no more. And if you were to see it you would never think that it was dye at all, for it looks only like rather yellowish water. But if it is squeezed out on a sheet of white paper, and laid in the sunshine, it very soon begins to change color. First it becomes green, then blue, and then purple. And it is really the dye which the ancient Romans valued so highly that no one who did not belong to the royal family was allowed to dress in purple raiment.

Borers

In many parts of our eastern coast occur in great numbers two or three kinds of small, rough, spiral gastropods, called borers by the fishermen, who hate them because of the great number of oysters they kill. Each of these spends its whole life in seeking and devouring other shell-bearing mollusks. It kills and eats these in a very curious way. Like all the gastropods, it possesses what we call a tooth-ribbon—that is, a narrow strip of very tough gristle in its mouth; set with row upon row of sharp, notched, flinty teeth. There are some times more than six thousand of these teeth, and although they are so small that they cannot be seen without the aid of a powerful microscope, they are nevertheless very formidable. For every tooth is hooked, with the points of the hook directed toward the throat.

The tooth-ribbon is used in this way: When a borer meets with a victim, it fastens itself to it by means of its fleshy, muscular "foot." Then it bores a round hole through its shell, as neatly as if it had been pierced by a drill. And then it pokes the tooth-ribbon down into the body of the creature inside, and draws it back again. As it does so, of course the hooked teeth tear away little bits of the victim's flesh. The borer swallows these, and then pokes down its tooth-ribbon once more. And so it goes on, over and over again, until the shell of its victim has been completely emptied, when it goes off to look for another.

Periwinkles