THE CLAM AND OTHER BIVALVES 169 



starfish (Fig. 118). There are various boring-snails, which 

 make round holes through one of the valves with their rasp- 

 ing-tongues and draw out what they need of the soft parts 

 (compare Fig. 99). Another enemy is the boring-sponge, 

 which, as it grows, makes holes in the valves by a secretion 

 which it produces. Like most other animals, the oyster has 

 its parasites. With all these facts before us, the statement 

 of Professor Mobius regarding the European oyster, that 

 each oyster when born has - - of a chance to survive 



J 1145000 



and reach adult age, seems well within reason. 



THE SCALLOP 



Habitat and Distribution. Of all the "shell-fish" that in- 

 habit the shallow waters of the Atlantic coast of our country, 

 none is more beautiful in color or in line than the common 

 scallop, Pec' ten irra'dians (Fig. 87). Scallops are abundant 

 among the eel-grass of shallow bays and inlets from the Gulf 

 of Mexico to Massachusetts Bay. Above the latter region 

 the waters are made colder by the Arctic currents. Pecten 

 irradians and many other species of sea-animals do not live 

 north of Cape Cod. There are, however, many species of ani- 

 mals that flourish best in the cold waters of Maine and the 

 maritime provinces of Canada. 



Relation to Environment. The very young scallop holds to 

 some fixed object after the manner of a young soft-shell clam 

 (Fig. 84). The adult scallop has no byssus, and only the 

 rudiment of a foot. The scallop in the foreground of the 

 picture is in what we might call the attitude of rest. It has 

 released its single adductor muscle, which, we may say in 

 passing, is the only part of the animal sold for food. The 

 mantle-folds of the resting scallop expand, showing at the 

 margin slender tentacles and a variable number of delicate 

 cobalt-blue eyes. If a person causes a shadow to pass over 



