SECRETS OF THE SALMON 



trout in shallow water taking natural flies on the 

 surface, and a dry fly passing by him several times 

 without his noticing it, because it was purposely 

 cast too far away and outside his window. It was 

 then made to float close to him, and he took it at 

 once, because it passed within his range of vision; 

 in other words, within his window. With this 

 explanation we can now understand what was seen 

 and photographed in the tank. I am not going into 

 the debated question of the eye of the fish. It 

 seems to me it is fair to assume that he sees the 

 visual image which is really there and that he sees 

 the same thing we do, with this difference: our 

 eyes combine to make one image and give a stereo- 

 scopic effect, while the eyes of the fish are inde- 

 pendent of each other. He probably does not 

 get any stereoscopic effect to help him judge dis- 

 tance. This may account for some of the times 

 he misses the fly. He sees a separate image with 

 each eye. Perhaps the reason we find salmon tak- 

 ing a dry fly more often when it is directly over 

 them is that then they have two images of the 

 fly and twice the brain stimulus. A fish's eye 

 seems to have a very large pupil, and therefore has 

 great light-gathering power, which enables him to 

 see in the dark, or rather when there is a very 



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