122 Descriptive Zoology. 



water clam. These clams may be picked up at low tide, 

 but are ordinarily take*n by means of long rakes or tongs. 

 The smaller or medium-sized ones are preferred. The 

 border of the inner surface of the shell is usually purplish, 

 and this part was made into the beads which constituted 

 the more valuable purple wampum of the Indians of New 

 England. 



The Oyster. One essential difference between the 

 oyster and the clam is that the oyster is stationary, 

 being firmly attached by one valve to some solid object, 

 a rock, or another oyster so attached. The oyster lies on 

 the left side, and the lower valve is much more concave 

 than the upper, which is nearly flat, serving as a lid. As 

 the oyster does not travel, it needs no foot and has none, 

 hence is less tough than the clam. The hinge is at the 

 pointed end of the shell, and the two mantle lobes are free 

 from each other, except near the hinge. There are no 

 siphons, the water entering all along the more curved bor- 

 der of the shell and passing out on the straighter side near 

 the larger end of the shell. The water is propelled by cilia 

 and passes through the gills as in the clam. There is but 

 one adductor muscle. 



Development of the Oyster. The eggs and young are 

 not carried nor protected as in the clam, but the eggs are 

 fertilized after being set free in the water. The egg 

 becomes many-celled by the growth and repeated division 

 of the one cell which constituted the egg. This becomes 

 ciliated and swims by means of these cilia. After a few 

 days of this free swimming life, during which time the 

 shell and other organs are gradually developing, the little 

 oyster attaches itself by its left valve to some submerged 

 object, to which it becomes firmly cemented by the deposit 

 of limy material which makes the hard part of the shell. 



