ASSOCIATION AND COLOR DISCRIMINATION 495 



sisted unchanged even when the relative intensities of these 

 lights were varied from 1.4 cm. to 4.9 cm. Differences in the 

 intensity of light passing through photographic plates 'fogged' 

 to a light and dark gray were not distinguished (pp. 475-483, 

 485). 



4. That sticklebacks form decided associations respecting the 

 color of the food which they habitually eat was further shown by 

 the experiment in which fourteen sticklebacks in an aquarium 

 were offered food and paper of various colors (pp. 483-484). 



5. Although the experiments summarized above show that 

 the discrimination of differences in colors by mudminnows and 

 sticklebacks is based upon wave-length rather than intensity, 

 it seems unlikely that the color vision of fishes is as highly de- 

 veloped as that of man, for sticklebacks, at least, seem unable 

 to distinguish between blue 420^ to 480^ and yellow 580^1 to 630^, 

 660m to 710/x. 



6. The results of the experiments with sticklebacks give little 

 support to the duplicity theory of v. Kries, but might be ex- 

 plained upon the basis of Bering's theory of opponent colors if 

 it is assumed that the yellow-blue substance is lacking. The 

 conclusions seem to accord with the Young-Helmholtz theory if 

 it is supposed that the eye of sticklebacks has none of the blue 

 component. 



7. The negative results in the experiments with patterns 

 strongly suggest that the discrimination of patterns and differ- 

 ences in backgrounds by mudminnows and sticklebacks does 

 not have a very important function in their search for food. 

 The perception of color and movement seem to be of the most 

 importance. In sticklebacks the sense of smell is also used to 

 a considerable extent. 



8. The behavior of fishes is stereotyped. The associations 

 formed are simple, few in number, and not open to ready modifi- 

 cation, though they may be fairly permanent, and may involve 

 considerable acuity in sensor}^ discrimination. ' Learning ' seems 

 to consist for the most part in the gradual elimination of useless 

 movements and the establishing of those which are useful. 



