456 GERTRUDE MAREAN WHITE 



once or twice did the}^ actually snap at the cotton packet. Then 

 perceiving the struggles of the rest of the fishes with the other 

 packet, they swam over and joined them. Repetition of this 

 experiment gave similar results. At Woods Hole, Massachu- 

 setts, the same test was performed upon Fundulus heteroclitus 

 for comparison, since this species had been found by Parker to 

 discriminate between the packets. The sticklebacks reacted 

 fully as well to the stimulus of concealed food as did Fundulus. 

 In the use of the sense of sight the mudminnow compares 

 more favorably with the stickleback, though the latter reacts 

 more quickly. Both species pursue moving objects without 

 odor, such as bits of paper, or objects above the surface of the 

 water; both exhibit skioptic reactions, and are stimulated by 

 an increase in the amount of illumination. 



COLOR DISCRIMINATION 



Notwithstanding numerous investigations, the question as 

 to whether fishes possess color vision is still somewhat unsettled. 

 Fishes live in a medium where, except at the surface, the light 

 is rather dim. The permeabilit}^ of water to light depends 

 largely upon its depth and clearness. There is an unequal ab- 

 sorption of different parts of the spectrum as rays of light pene- 

 trate; the red end is absorbed more rapidly than the blue, so 

 that at a depth of several meters in clear water fishes see as if 

 through a blue-green glass. This fact might lead one to the 

 view that for fishes living at any great depth, the ability to dis- 

 criminate colors would be valueless. There is the possibility, 

 however, that the eye of such fishes is better adapted to perceive 

 minute differences in shade and color of objects in a dim light 

 than is our own — a consideration which should not be rejected 

 because .fishes are rather unspecialized in structure compared 

 with other vertebrates. Even though fishes, w^hich live at a 

 depth where red, orange, and yellow rays of light do not penetrate, 

 may have no use for a color sense, this cannot be true of fishes 

 living and feeding at the surface, where rays of light are only 

 slightly refracted and absorbed by the water. 



In dealing with this problem there are certain questions to 

 be considered: 



