2IO THE SENSES OF ANIMALS 



dolphins have no functional whiskers of this sort, but then 

 we know they have a very efficient sonar system for use in 

 such surroundings. 



The largest whiskers of all are found in the walrus, but 

 in this animal they have been put to a different use, although 

 they may of course retain their tactile function to some 

 extent. In the walrus they are used as spoons for feeding. 

 The walrus lives largely on clams which it digs out of the 

 mud at the bottom of the sea with its tusks, and it uses its 

 bushy whiskers for shovelling them into its mouth when it 

 has dug them up. 



Among the other aquatic vertebrates whisker-like struc- 

 tures are commonly found in the fishes. The barbels of fishes, 

 however, although similar in function as organs of touch, 

 are very different in structure. Hairs are non-living products 

 of the skin, but barbels are extensions of the living part of 

 the body, and consist not only of skin but of some of the 

 underlying supporting tissue as well. Their mode of action, 



Fig. 1 6. a Catfish [Saccobranchus) showing the barbels on the snout and lower 

 jaw. 



too, is different; they are richly covered with touch end 

 organs so that nerve impulses can start in their very tips 

 whereas impulses can start only from the cells surrounding 

 the bases of hairs. The most familiar barbels are those on 



