LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 71 



the blue, according to Hess' explanation, is greatly reduced 

 in its effect by being absorbed by the pigment which in 

 the light-adapted eye has drawn forward and therefore 

 must absorb the light before it reaches the ends of the 

 rods and cones. In Bauer's work the dark-adapted fish 

 in entering the red may have been giving a negative re- 

 sponse to a too brilliant blue, a blue past the optimum 

 because of the retractions of the retinal pigment. The 

 red, however, had not so increased in brightness and was 

 entered. The dark-adaptation had increased sensitivity 

 to brilliant blue light. The fact that fish tend to go to an 

 optimum light will equally well explain the behavior of 

 the fish used by Hess when they are recorded as going to 

 a red after light adaptation and entering the blue half of 

 the container when the blue was increased in brightness 

 six to eight times. This would be expected for fish where 

 red avoidance is absent as it is in Mugil according to Bauer. 

 Frisch (1912) placed fish in glass-bottomed dishes with 

 colored papers beneath them and found that they became 

 of a brightness and color like the background upon which 

 they rested. The stimulus for this matching is received 

 through the eye.-' He found that the fish changed their 

 brightness tone before they changed color. When he used 

 at the same time papers of different colors he found that 

 with properly selected colors the fish could be shifted from 

 one to another without change in their brightness tone. 

 Such colors were thought to be of matched brightness for 

 the fish. After a time these fish changed color to match 

 the background, thus indicating that the color change is 

 a response to wave-length and not to brightness. In other 

 experiments Frisch fed his fish from the upper end of a 

 glass tube lined with a certain color. This tube was placed 

 in an aquarium as a member of a series of tubes with linings 

 varying from white, through a series of grays, to black. 

 To make impossible a choice by position the order of the 

 colored tube in the series was changed from time to time. 

 When the fish had learned to seek food only in the colored 

 tube, one similar in color but empty was substituted. The 

 fish continued to seek food in the colored tube. As they 



^ See Parker 1909, Mast 1916. 



