Flies and Fly-fishing. 387 



eye is identical with the photographic camera in its 

 mode of adjustment to distance, except that in the 

 camera a sharp image is obtained by moving the plate- 

 holder (the retina) nearer to or farther from the lens, 

 whereas in the fish's eye the retina remains stationary, 

 and it is the lens itself which is moved. The conclusion 

 seems necessarily to follow from Beers's researches that 

 the vision of fishes is not so defective as anatomy and 

 optics had led us to suppose. Still we must not run to 

 the other extreme. The very great difference in the 

 transparency to light of air and water must by no 

 means be overlooked, a difference accentuated by the 

 suspended matter which unfiltered water always con- 

 tains in considerable quantity. If this important factor 

 is given due weight, it would still seem that the vision 

 of fishes is quite limited, and must vary markedly with 

 the optical purity of the water in which they are found. 



Is not the action of trout towards the artificial fly just 

 what this would lead us to expect ? Place the natural 

 insect and its artificial copy side by side, and is the re- 

 semblance sufficiently close to deceive the human eye for 

 a single moment? Though in color they may be ap- 

 proximately similar as to form, only the eye of char- 

 ity can detect a resemblance. In no element is the 

 struggle for life so bitter. To eat others and to avoid 

 being eaten are the sole occupations of the greater part 

 of a fish's life. Constant vigilance against the approach 

 of their many enemies is with them the price of life; 

 therefore, nothing terrifies them so much as motion, and 

 all the more since their imperfect vision fails accurately 

 to apprise them whether the moving body is friend or foe. 



The foregoing applies to leaders as well as to any 

 other moving object; and since at some point between 



