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BEGINNERS' ZOOLOGY 



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 centre? 



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 the blood current are brought in close contact? 



The three main classes of molluscs are: the pelecypoda 

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

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



Comparison of Mollusks 



Shell 



Head 



Body 



Foot 



Gills 



Eyes 



Mussel 



Snail 



Squid 



