io8 



ANIMAL BfOLOGY 



Why is a smooth shell suited to a clam and a rough 

 shell suited to an oyster ? Why are the turns of a snail's 

 shell so small near the center? 



Why does the mussel have no use for head, eyes, or pro- 

 jecting feelers? In what position of the valves of a mussel 

 is the hinge ligament in a stretched condition ? How does 

 the shape of the mussel's gills insure that the water cur- 

 rent and blood current are brought in close contact ? 



The three classes of mollusks are : the pelecypoda 

 (hatchet-footed); gastropoda (stomach-footed); and cepha- 

 lopoda (head-footed). Give an example of each class. 



Comparison of Mollusks 



