The Senses and the Nervoiis System 1 1 3 



TOUCH 



Touch is the most fundamental sense in the animal king- 

 dom. It exists in the lowest forms, and it is probable that 

 many of the other sense-organs of the higher animals were 

 derived from organs of touch. In the fish, the touch papillae 

 are spread over the surface of the skin, as they are in man. 

 The whole system is so similar to our own that we do not 

 need to go into it here. 



SMELL AND TASTE 



The senses which have been discussed so far are all alike 

 in that they may be called physical senses: they all receive 

 physical phenomena — sound-waves, light-waves, heat, pres- 

 sure, contact — and transform them into nervous energy. The 

 two remaining popular senses, smell and taste, are, in con- 

 trast, chemical senses: they transform chemical phenomena 

 into nervous energy. 



That the sense of smell is present in fish has long been 

 believed by dam-tenders and small boys from their experi- 

 ences with lampreys. Lampreys are primitive, jawless, finless, 

 eel-shaped, fish-like animals which make a living in the 

 ocean by attaching themselves with their suctorial oral disks 

 to decent fish and gouging out flesh and blood with their 

 rasp-like "tongues." Like the salmon, they come into fresh- 

 water streams to spawn, and are often found in great num- 

 bers at dams, being able to surmount low ones by attaching 

 to the surface with their oral disks and hitching upward like 

 "inch-worms." If you spit in the water above such an aggre- 

 gation of lampreys, they loosen their hold and dash off in 

 all directions, presumably because of the repulsive or fear- 

 inspiring odor of human saliva. On a different level, palaeon- 

 tologists have long believed that the sense of smell exists in 

 fish because they have found in fossil fishes hollows in the 



