THE PERCEPTION OF COLOUR 



625 



response was given to red and blue alike. This reasoning, as we have 

 already seen, is quite invalid. On the other hand, Bauer (1909-11), 

 working with several species {Charax, Box, Atherma, 3Iugil, etc.), 

 found evidence of hue-discrimination ; light-adapted fish were 

 found to avoid red, dark-adapted specimens to prefer it, a suggestion 

 of the presence of a Purkinje phenomenon. Shortly thereafter von 

 Frisch (1912-25) initiated a long series of experiments based both on 

 the dermal responses to coloured backgrounds and on training. 



With a view to interpreting the significance of dermal changes to 

 conform with the background, which are mediated through the eyes,^ 

 von Frisch (1912) used a species of minnow, Phoxinus, which changes 

 colour rapidly in resjDonse to the brightness of the background and 

 turns yellow slowly on a yellow-red background. He was able to match 

 the luminosity of grey backgrounds with yellow so that the rapid 

 change was abolished but still found that after an interval the fish 

 turned yellow on a yellow background but never on that of a matched 

 grey or other colour. He therefore concluded that there was a response 

 to colour different from the response to luminosity. Further work on 

 other species of this fish was in some cases inconclusive (Freytag, 1914), 

 in other cases corroboratory (Haempel and Kolmer, 1914 ; Reeves, 

 1919 ; Schnurmann, 1920). Using the teleostean Crenilabrus, which 

 reacts to red, yellow, green and blue backgrounds, v. Frisch (1912) 

 again fovmd that its pigment cells reacted to hue rather than brightness, 

 a conclusion substantiated by the observations of Sumner (1911) and 

 Mast (1916) on the teleostean flat-fishes which change their pattern of 

 colour rapidly and dramatically to suit the changing environment while 

 swimming over a coloured sea-bottom.^ 



Final corroboration of this general conclusion has been obtained 

 by the study of more objective responses. Reeves (1919), for example, 

 experimenting on fish (the mud-fish, Umbra, and the shiner, Notrojns), 

 found that the respiration rate increased considerably when the 

 illumination was increased but was more than doubled when white 

 light was changed to red even although its intensity was simultaneously 

 diminished — strong presumptive evidence that red was appreciated 

 differently from white. Bull (1935), employing electric shocks to 

 establish conditioned reflexes on the basis of hue -discrimination in 

 the blenny, Blennius pholis, came to the same conclusion ; while 

 Thibault (1949), basing his observations on the fact that light exerts a 

 tonic influence initiating a change in posture when the two eyes are 

 unequally stimulated, brought forward striking evidence that the 

 peripheral mechanism in the retina of the carp, Cyprinus, contained 

 receptors which were individually sensitive to red, green and blue- 

 violet. 



Phoxinus 



Blennius 



1 p. 82. 



p. 92. 



S.O.— VOL. I. 



