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GENERAL ZOOLOGY 



Fig. 111. Group of living pond snails. (Natural size) 



such times one can see the mouth open and the tongue 

 sweep back and forth, with tiny, rhythmic movements. 

 The two tentacles are organs of touch. The eyes lie one 

 in front of either tentacle at its base. On the right side, and 

 partly beneath the edge of the shell, is an aperture which 

 opens over a small hollow space in the body when the snail 

 comes to the surface. This space is the so-called "lung" of 

 the pond snail. The lung is adapted to using the oxygen of 



