OYSTERS, CLAMS, MUSSELS 225 



six pounds and has a siphon that may be extended eighteen to 

 twenty-four inches. The body is very large, but the shells are 

 so small that they only cover the sides of the clam and the 

 great white mass that extends beyond the shells and the long 

 siphon looks not unlike the breast and neck of a duck, the 

 shells representing the folded wings. 



In the hard, smooth, wave-beaten, sandy beaches of the 

 North Pacific are to be r jund the "razor-clams," Machera 

 patula, which are undoubtedly the finest of all the clams. 

 The meat is white and tender and most delicately flavored. 

 The canneries tnat have been established along the coast are 

 fast depleting the supply of these choice clams. 



Oysters. Much more important than the clams, though 

 less numerous, are the oysters, two species of which occur 

 along our coasts and are used for food. Some of the most 

 extensive natural beds occur in Chesapeake Bay, but other 

 beds are found as far north as Prince Edwards Island and as 

 far south as the Gulf States. Many excellent beds are found 

 in Long Island Sound. The eastern oyster, Ostrea virginiana, 

 is unisexual, that is, the ova and spermatozoa are produced in 

 different individuals. During spawning season the female 

 produces sixteen to sixty millions of ova which are set free in 

 the water to meet by chance the spermatozoa from the male. 

 If this union takes place, the ova are fertilized and soon lose 

 their original pear shape and become quite round. If they 

 are not fertilized they soon perish. Within two or three hours 

 after fertilization these ova, which are single cells too small to 

 be detected with the unaided eye, begin to divide, and in two 

 hours more have changed from single round cells into masses 

 of cells, the masses themselves being rounded and about the 

 size of the original egg cell. A little later, small thread-like 

 projections, or cilia, begin to appear on one side. The embryos 

 have now reached the swimming stage, for by means of these 

 cilia they are able to move about through the water at will. 

 They remain in this stage from three to six days, or until the 

 shells have begun to form, when they sink to the bottom, and, 

 if they are fortunate enough to strike some suitable hard object, 

 they become attached and begin to take on the character of an 

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