CLAMS, OYSTEKS, AND MUSSELS 



113 





the mud within reach of the sea water. In this pooition a 

 stream of sea water carrying food and air goes down one 



tube, is ehiven through the gills, ^=^ -, 



and finally back up the othei 

 tube to be poured into the sei 

 above. 



Oysters. — They are similar m 

 structure to a mussel, except 

 that they have no foot, or only a 

 rudimentary one, anil no siphons 

 and the valves of the shell aie 

 unequal. One valve is hollowed 

 out to receive the body of tht 

 oyster, and the other valve is 

 nearly flat. Usually the hollo\\ 

 valve is attached to some' sub 

 merged object. They Hve all 

 along the Atlantic coast south ot 

 Cape Cod, and along the Gulf 

 coast. Oysters are, probabh 

 most extelisively grown in the 

 Chesapeake Bay. Their eggs 

 which are produced in greit 

 c^uantities, soon hatch, and, aftei 

 a few days of a free-swimming 

 life, the young oysters attach 

 themselves to some objects, usually old shells, and begin 

 growing in earnest. It takes an oyster from three to five 

 years to become of marketable size. In making artificial 

 beds, old shells, pieces of earthenware, and slate are throwm 

 into the water for places of attachment for the oysters. 

 Oysters live on minute plants and animals found in fresh 



hekkick's zool. — 8 



Fig. 60. — Long clam in its 

 burrow. 



