Page:Popular Science Monthly Volume 50.djvu/60

48 this: When the eggs are set free in the water they soon hatch, and the little ones swim about until they find some fish to which to attach themselves. They live for a time on the mucus of the fish and then drop off, sink to the bottom, and form burrows for themselves. This curious semiparasitic life is no doubt a reversion to the habit of some ancient ancestor.

The white-shelled clams live in sand, the black-shelled in mud. Besides living on the seacoast, clams inhabit all United States fresh waters, and in some New York and Western rivers clams have been found which contained pearls of great beauty and considerable value. I have never seen anything more exquisite than the pink pearl lining of some river clam shells.

The razor shell, familiar to all on account of its universal distribution, belongs to the clam family. It has a powerful foot, with which it can scoop out a passage through the sand faster than a man can dig with his spade. One of the clams inhabiting warm inlets south of Boston is the quahog. The shells have a finely beaded edge and are partly lined with deep violet. It was from this that the New England Indians made their purple "wampum" (money), which was considered twice as valuable as the white "wampum." The old-time spelling of clam, clamp, was characteristic of one of its chief features, the two halves being so tightly clamped together.

The oyster, a close relation of the clam, is perhaps the most useful and valuable member of all the molluscan group to mankind. The left half of the shell is generally attached to some submerged object and is quite hollow, for it is in this half that the body lies, the upper or right half being almost flat. The oyster readily adapts its shell to surrounding objects, growing about them in most fantastic ways.

When a grain of sand or any minute particle gets in between the oyster's mantle and the shell it is very irritating, and causes a great excretion of matter to take place. This collects around the nucleus in concentric coats like those of an onion. If the lining of the shell be mother-of-pearl, these coats of matter which cover the little grain of sand will also be pearly, and perhaps form a gem of priceless value. Sometimes one of the oyster's own eggs lodges between mantle and shell and is transformed into a wonderful tear of rainbow hues. It is only those shells having a pearly or nacreous lining which can form these gems. For hundreds of years pearl fishing has been a lucrative industry. The most renowned fisheries are at Panama, Ceylon, and in the Red Sea. The pearl oysters are very large, live in from six to twelve fathoms of water, and are gathered by diving.

Pliny calls the scallops (Pectinidœ) butterflies of the sea. They are very shy and live in the midst of the eel grass, where the