ASSOCIATION AND COLOR DISCRIMINATION 483 



of the acquired association was demonstrated by the fact that 

 during the twenty days following the fish persisted in attempting 

 to take the paper under the green light which had previously 

 shone upon its food. The reversal of the colors seemed to con- 

 fuse the fish, and an errorless record with the new conditions 

 was never shown as in the previous test. It required a much 

 longer period to form the habit of taking food in red light and 

 refusing paper in green light than to form the first association. 

 The entire experiment lasted ninet}^ days, January 5 to April 3 

 (fig. 8, A; table 3). 



Stickleback no. 50 learned to react negatively to paper offered 

 in red light and positively to food in green light in a series of 

 tests continuing thirty-two days, at the end of which there was 

 a perfect record of fifteen days. Stickleback no. 50 reacted in 

 the same manner to the reversal of colors as had stickleback 

 no. 46. The association of food with green light was overcome 

 with great difficulty, but after seventy-one days of experiment 

 had elapsed, the fish was tested on ten successive days without 

 errors being made. Although the light intensity was varied for 

 the last twenty-three days of the experiment, the oscillations of 

 successes and failures which took place seemed not to be corre- 

 lated with the relative intensities of the lights, and it may be 

 noted in the tabulated results (table 2) that the highest percent- 

 age of successes for the whole experiment was recorded during 

 this period (fig. 8, B). 



Like the mudminnows, the sticklebacks tested showed that 

 they were able to distinguish between red (600 /x to 730 ^u) and 

 green (510/x to 570 /x), but the experiments indicated that with 

 blue (420m to 480 m) and yellow (580/^ to 630^, 660^ to 710/x) there 

 was no such discrimination. 



Experiment with an aquarium of sticklebacks 



An interesting piece of evidence was obtained from an aqua- 

 rium containing fourteen sticklebacks. These fishes were kept 

 under observation for several months, during which they were 

 regularly fed and became very tame. Calves' liver was given to 



