The Senses and the Nervous System I2i 



or the enemy really dangerous. To be sure, fish can learn. 

 We all know trout that have learned to avoid flies with 

 visible lines attached to them. But here again we may permit 

 ourselves to guess that it is probably not so much a case of 

 the trout saying to itself, "There is what looks like a nice 

 morsel, but it has a line tied to it, and flies with lines tied 

 to them hurt, and trout that eat them go away and do not 

 come back," as it is a case of, "Line on water . . . run and 

 hide" — just as pure a primary reflex action as when you pull 

 your hand away from a hot stove. 



Trying to imagine what goes on in the fish's brain is a 

 dangerous proceeding, and one wholly unbecoming to a 

 scientist, but it is permissible to a layman, and any layman 

 who did try it might not be far wrong if he concluded that 

 a fish on the end of a line had a dull sensation of physical 

 pain at the point where the hook held it 5 that it felt fear 

 and discomfort from the restriction of its movements 5 and 

 that it learned that a line was a thing to avoid, to the point 

 that in future, provided it succeeded in having a future, it 

 ran for cover each time it saw one. But that this fish hence- 

 forth went about in fear of lines, or that it bore in its mind 

 a memory of the pain caused by a hook, or even that the 

 sight of a line brought back to its mind the pain caused by a 

 hook, would be an unjustifiable conclusion. 



And in this connection the question of how much fish 

 actually learn is worth taking a look at. We speak of "edu- 

 cated trout" in certain streams, and we say that the larger 

 fish are harder to catch because they are older and have had 

 a chance to learn more. Obviously fish do have a capacity for 

 learning — that has been proved by laboratory experiment as 

 well as by field observation — but just as obviously, all the 

 fish that are hard to catch have not had personal experience 

 with the hook which has taught them to avoid it. Do we 



