STRUCTURE 



95 



Showing mantle and muscles, a.a. an- 

 terior adductor muscle ; p. a, pos- 

 terior adductor muscle. 



thus forming two openings known as siphons (si 'tons). 

 Through one of these siphons water enters, carrying food 

 and oxygen. Through the other the water passes out, 

 carrying the waste from 

 the body. 



Between the mantle 

 and the body proper are 

 gills, which hang free in 

 the shell cavity. The 

 gills are filled with holes 



through which the water Figure 94. — Right Shell of Clam 



passes. 



The foot is attached 

 directly to the body 

 proper and is the part of the clam hard to chew when it 

 is eaten. The foot and body form a solid mass that nearly 

 fills the space between the shells. 



The two valves of the clam shell are held together by 

 means of strong muscles, attached to each shell. One of 

 these is located in front of the body and is known as the 



anterior (front) adductor 

 (ad-diik'ter) muscle: the 

 second is just back of the 

 body and is the posterior 

 (back) adductor muscle. 

 When these two muscles 

 contract, the two valves 

 are held tightly together. 

 Before the live clam can 

 be examined these two 

 muscles have to be cut, as it closes its valves when 

 handled. When the clam is dead, these muscles relax and 

 the hinge forces the valves apart. It is not safe to eat 

 clams and oysters that have died in their shells. 



Figure 95. — Digestive Tube of Clam 

 m, mouth ; s, stomach ; i.c, intestine. 



