MOLLUSCA. 71 



1. The soft body located in the dorsal region. 



2. The foot, a firm muscular structure on the ventral 



edge of the body. 



3. The gills, large flap-like membranes on either side in 



the posterior portion of the cavity. 



4. The palps, small flap-like structures at the anterior 



part of the body on each side of the mouth. 



5. Identify the inhalent siphon which leads into the 



mantle cavity. The other, more dorsal opening is 

 the exhalent siphon. 



6. Make a diagram showing the clam in cross-section, — 

 (a) in the region of the umbones ; 



(6) in the region back of the umbones. 



7. Examine a prepared specimen of a portion of a gill. 



(h.p.) Sketch. 



8. Test the circulation of water in the live clam by 



placing a drop of ink in the water near the siphons. 

 (Dem.) 



9. The gills of the clam are often distorted by the 



presence of egg masses. 



H. Suggestive Questions. 



1. Just how does a clam use its foot for locomotion? 



(Observe live clams in the laboratory.) 



2. What is the position of the clam in the mud? 

 Why? 



3. Why does an oyster have two unlike valves? 



4. How can an animal so well protected by a shell as 



the clam or oyster be eaten by the starfish? 



5. What is a " mussel " ? 



6. What effect, in the course of long evolution, has the 



heavy protective shell had upon the clam ? 



