304 The Trout s of America 



streams is due to the action of the nerve of the 

 eye on the color glands, for when the fish be- 

 come blind they always assume a dark coloration ; 

 when the nerve of the eye ceases to act, the color 

 glands lose their motive powers. Through our 

 eyes we receive perceptions of color, shades, or 

 tints, which are transmitted to the brain; in 

 fishes through the same medium, the nerve of the 

 eye, these impressions act upon the color glands, 

 and are of course involuntary and entirely beyond 

 the control of the fish. Upon dark-colored fishes 

 living in cave-streams or underground lakes, a 

 similar cause and a like effect constantly exists ; 

 the fish cannot see, for they live in perpetual 

 night. Why trout are found in their native 

 waters on which the glare of the sun or the sub- 

 dued light of the forest gloom are constant condi- 

 tions, the fish being without the characteristic 

 red spots, and now and then assuming the abnor- 

 mal coloration of the albino, is a difficult matter 

 to explain ; it doubtless arises from the defective 

 action of the nerve of the eye upon the color 

 glands, or petals, which lie under the scales and 

 which open and shut when under the influence 

 of color tints conveyed to them through the 

 delicate nerve of the eye ; certain nerve fibres in 



