Seeing^ Hearing, and Smelling 53 



to collect sensations of smell from the surrounding- 

 waters. They are therefore known as rhinophoves or 

 nose-bearers. 



The sense of touch is acute, as must be obvious 

 to anyone who has handled almost any species of 

 mollusk. Creatures of such soft substance must 

 necessarily be very sensitive in this direction or they 

 would meet with many injuries. To touch a snail, 

 however lightly, is to cause it to shrink into its shell 

 at once. A slug has no shell that it can crawl into 

 on being molested, but it instantly draws in its eyes 

 and antennoe and hunches the body up into a thick, 

 short heap that exposes the minimum of surface to 

 attack. In many of the shelled species the margin 

 of the mantle is cut up into lobes and filaments 

 which are all very sensitive to touch, and in some 

 there is in addition a pair of protruding palps near 

 the mouth that serve as tactile organs. These palps 

 are also present in the bivalves but there, except in 

 special cases, most of the tactile work is performed 

 by the foot and the siphons. 



