COLOR VISION IN FISHES 477 



would bring about an equal distribution of the animals. These findings 

 were directly contradictory to those of Hess, irrespective of any differ- 

 ence of interpretation; for Hess had claimed that an intense red and a 

 blue were responded to alike and perceived alike, and that Atherina 

 hepsetus responded differently to white lights differing as little as by a 

 1 : 1.23 ratio in brightness. Later work by others has substantiated Bauer's 

 contention that the intensity-discrimination of fishes is extremely poor. 

 Of course, it is probably mostly a matter of attention-value, the intelli- 

 gence of the fish not being up to par with its sensations. 



Bauer's animals were, it is to be noted, thoroughly light-adapted. Dark- 

 adapted specimens showed no red-shyness, and would freely enter red or 

 orange illuminations (^620-630m|l) which, when they were light-adapted, 

 would frighten them over to the dark side of the choice-box. No sudi be- 

 havior was noted toward any intensities of white light except very high 

 ones. Far from being blind to red as Hess claimed, the animals perceived 

 it very vividly according to Bauer. When dark-adapted, they preferred red 

 to a blue which Bauer considered to be of the same intensity. Therefore, 

 he thought, the chroma disappeared from the red wavelengths sooner 

 than it would for the dark-adapted or dark-adapting human. Both a 

 photochromatic interval for red, and a Purkinje phenomenon, seemed 

 to have been established for the species. 



When spectral lights were used, the fishes did not prefer the yellow- 

 green as Hess had claimed, but went to either yellow or blue-green. It is 

 interesting to note that the photopic human has a secondary maximum 

 of brightness in the blue region (unless the macular pigment happens to 

 be excessive) . The two maxima are perhaps more nearly equal in bright- 

 ness for Bauer's species. 



When the wavelength of a spectral light was moved gradually up from 

 the violet end, the fishes first made definitely negative responses at A,510- 

 m[l, and under a red filter (^680-710m|l) they would scatter into dark 

 comers if light-adapted, gather under the filter only if dark-adapted so 

 that its redness was not apparent to them. This seems further evidence 

 for a photochromatic interval for red (which does not occur in man) , 

 though no one seems to have pointed it out. 



Mugil, being positively phototropic and lacking in red-shyness, lent 

 itself to certain experiments impossible or inconvenient with the other 

 species. Bauer paired a green light with a blue one and regulated their 

 intensities so that the fishes gathered in the green. When both lights 

 were reduced equally in intensity the animals shifted over into the blue 



