COLOR VISION 359 



Moreover, the probability that its discrimination was 

 based upon brightness was greatly lessened by using, when 

 we experimented without food, a different red much lighter 

 than that in the food tests. The fish successfully discrimi- 

 nated red from blue paints in the same way, and it was 

 afterwards trained, by putting food in the green fork, to 

 break the earlier association and bite first at the green." 



Reighard made his experiments on a school of gray 

 snappers, a form which usually inhabits the water under 

 a dock at one of the Dry Tortugas Islands. The gray 

 snappers feed on atherina, a small fish found in abundance 

 near the shore. They take these fish, even if they have 

 been killed in formalin and stained any color, but if Cassi- 

 opea tentacles are fastened to the atherinas they soon learn 

 to avoid them. After the gray snappers had learned to 

 reject red atherinas with tentacles it was found that they 

 also rejected red ones without, but that they still took 

 those stained any other color. For example, when blue 

 and red atherinas were thrown in together they took only 

 the blue, and this was true even if some of the red ones 

 were of a much brighter shade and others of a much darker 

 shade than the blue ones. 



This seems to prove that the selection could not have 

 been due to difference in brightness, such as a color-blind 

 person can perceive in the different colors, and it led the 

 author to conclude that ^ray snappers have color vision. 



It will be seen that the conclusion that fishes have color 

 vision, both in the work of Washburn and Bentley and in 

 that of Reighard, rests primarily upon the fact that the 

 animals discriminated between red of different shades and 

 blue or green, and upon the assumption that the brightness 

 of the different parts of the spectrum is practically the same 

 for fishes as it is for man — that their eyes are stimulated by 

 all the rays from the infra-red to the ultra-violet somewhat 

 as ours are. While this may be true, it has not been posi- 

 tively demonstrate-d. As a matter of fact, there are reasons 

 for believing that the red end of the spectrum for fishes 



