The Senses cmd the Nervous System 67 



that we have, it would be their popular conception that they 

 have six senses. For in addition to our five traditional sense- 

 organs, which we inherit from them, they have a sixth, the 

 lateral line. What appears to us to be just a pleasantly orna- 

 mental stripe running along the side of the fish from gills to 

 tail, and carrying out the stream-lining in much the same 

 way that the body-stripe does on a modern automobile, is 

 in reality a distinct and extremely important sense-organ. 



How many of the four additional senses mentioned above 

 are possessed by the fish is one of those questions which 

 science will probably never be able to answer fully, for it is 

 obviously impossible to know fully what the fish's sensations 

 are. And this applies to all his senses, even to those whose 

 workings we understand best, such as sight. What another 

 human being sees we can tell with some assurance from what 

 he says. What a dog sees we can imagine from his reactions, 

 which, from his closeness to us, we assume to have the same 

 significance as our own. But what a fish sees, in a different 

 medium, with different reactions, and with an optical ap- 

 paratus differently constructed from our own, is not an easy 

 problem. It is regrettable that no one, even with the best 

 intentions, has ever succeeded in turning himself into a fish. 



SIGHT 



The fish has two eyes, even as you and I. From this we 

 permit ourselves to conclude, without further argument, 

 that the fish sees. From an analysis of his actions and an 

 examination of his brain, we conclude that eyes are to him, 

 or at least to such of him as we are most interested in, the 

 most important of the sense-organs, even as they are to us. 

 But when we come to trying to find out what his eyes see we 

 cannot go so fast. 



