ASSOCIATION AND COLOR DISCRIMINATION 485 



Experiments with gray filters 



Gray filters were presented alternately to the two sticklebacks 

 no. 65 a;nd no. 66 exactly as they had been offered to mudmm- 

 nows no. 55 and no. 60. It may be noted that these were the 

 same sticklebacks which had been subjected to the experiment 

 with yellow and blue lights and to the experiii.ent with red 

 and green ; both had manifested the power to discriminate 

 between red and green. In contrast the experiment with 

 the gray filters was very striking, for on no occasion does the 

 record show a day without error for either fish. Neither of the 

 curves touches the point at at any time during the experiments 

 (fig. 7, E, F; table 3). 



Summary of results in regard to color vision of sticklebacks 



1. Sticklebacks were not able to distinguish between blue and 

 yellow lights of the following wave-lengths: 420/^ to 480/i and 5S0fx 

 to 630^1 and 660/x to TlO^u. 



2. Red 600/x to 730^t and green 510/x to 570fx were distinguished 

 even when the relative intensities of these lights are varied from 

 1.4 cm. to 4.9 cm. 



3. Photographic plates 'fogged' to a light and a dark gray 

 were not distinguished. 



4. Sticklebacks form decided associations respecting the color 

 of the food which they habitually eat. 



GENERAL CONCLUSIONS ON COLOR VISION IN FISHES 



The experiments described in this paper and the work of other 

 investigators furnish evidence that some species of fishes perceive 

 differences in colors, and that this discrimination is based upon 

 the wave-length of the light, not on intensity. It seems rather 

 unlikely that the color vision of fishes approximates in character 

 that of human beings.' It would be of interest to know what 

 range of colors fishes react to. The stickleback, at least, seems 

 unable to discriminate between blue (420^t to 480/i) and yellow 

 (580/x to 630ju, 660^1 to 710/x). Whether these colors are con- 

 fused by mudminnows also has not been tested. 



