Sensory Discrimination: Vision i6i 



ceps was ruled out, and the fish could identify the red 

 ^forceps whether_they were to the human eye darker or 

 lighter than_.the^ green. It is not, however, a sufficient 

 guard against the brightness error to use human judgments 

 of brightness as a standard. Reighard (631), similarly, 

 trained the gray snapper to avoid minnows dyed in certain 

 colors and select those dyed in other 'colors, several bright- 

 nesses differing to the human eye being used, but the 

 brightness error not being more fully eliminated. Bauer 

 (27) believes he has secured evidence that fish discriminate 

 colors, and that certain fish are afraid of red, but the gen- 

 eral character of his methods and conclusions does not 

 inspire confidence. Hess (304, 308) is convinced that the 

 spectrum is seen by fishes with the same distribution of 

 brightnesses that is characteristic of the color-blind human 

 eye, and makes the inference, which we have previously chal- 

 lenged, that total color-blindness must exist in such a case. 

 Von Frisch (245), on the other hand, argues that fish possess 

 color vision. He has shown their ability to pick out a 

 color from a whole series of grays. He points to the fact 

 that in the spawning season many fish assume bright 

 colors and patterns ; these, he urges, must have some in- 

 fluence in bringing the sexes together (243). Hess (310) 

 in opposition to this points out that such colors would not 

 be visible below a certain depth of water ; Von Frisch re- 

 plies that most of the fish which show them spawn in 

 shallower waters. One can hardly, however, infer color 

 vision from the existence of such colors, for they may be 

 only incidental effects of the physiological state of the 

 animals, and without any influence on their behavior. A 

 more persuasive line of argument is derived from the way 

 in which various flatfish change their markings and colors 

 to suit the ground on which they lie. Von Frisch (240) 



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