48 POPULAR SCIENCE MONTHLY. 



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 rever- 

 sion 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 con- 

 siderable 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 dis- 

 tribution, 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 " wam- 

 pum" (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 man- 

 kind. 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 oys- 

 ter 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 lin- 

 ing 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 indus- 

 try. 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 (Pectinidce) butterflies of the sea. They 

 are very shy and live in the midst of the eel grass, where the 



