PHYSIOLOGY OF THE LWERTEBRATA. 



381 



sucker at the tip. " When the animal is not walking, these 

 feet are nevertheless in a constant state of movement, and 

 their movements are then of a peculiar writhing, almost 



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vermiform character — twisting about in various directions, 

 and frequently coiling round each other. When fully pro- 

 truded, however, they are perfectly straight and stiff." A 



