494 ADAPTATIONS TO PHOTIC QUALITY 



To sum up Birukow's work : He has not demonstrated that the frog 

 necessarily has any reactivity to hue. If his animals were responding to 

 hue by such a pure reflex as the optomotor reaction, we can tell no more 

 about whether they have hue sensations, by means of Birukow's proce- 

 dure, than we could with a conditioned-reflex technique. If we even 

 assume that Birukow's conclusions are justified (correcting the one 

 regarding blue) then we must believe that the frog has a 'red' sensation, 

 but no hue sensations from medium and short wavelengths — his neutral 

 point is really a neutral region, which nearly fills his spectrum. But if the 

 animal does also see blue as Birukow claims, then the frog stands reveal- 

 ed as the only known vertebrate whose color-vision system is dichromatic 

 and has a neutral region instead of a neutral point. Until much better 

 evidence than Birukow's is produced, we had best conclude tentatively 

 that the Amphibia have no color vision whatever. 



Reptiles — Aside from the age-old supposition that the chameleons can 

 change color to suit any and all backgrounds, and do so because they 

 see the colors of the backgrounds, the writer has been able to unearth 

 only one statement about reptilian colorvision from the dark ages of 

 comparative psychology. It was made regarding the common European 

 turtle (Emys orbicularis) by an old-time French naturalist. He found 

 that when this carnivorous species is offered a rose leaf, it will ignore it 

 and try to seize the proffering finger; but when offered a rose petal the 

 turtle grasps it at once "because it is the color of a piece of raw meat." 

 This sort of experiment is interesting, but no more than that; and a large 

 portion of its interest lies in the belief inherent in the investigator, and 

 so widespread among laymen, that if any animal can distinguish any 

 hues it should at least be able to recognize those of foliage and blood — 

 the two most important colors for herbivores and carnivores. It seems 

 almost illogical that the hues yellow and blue should be so favored by 

 psychologists as the 'most primitive' colors in hypothetical phylogenetic 

 schemes of human color vision! 



Not until recently was any real investigation of reptilian color vision 

 made, apart from the inevitable pupilloscopic studies and food-visibility 

 experiments of Hess, which showed a shortening of the short-wave end 

 of the spectrum, as in diurnal birds. In 1933, Wojtusiak published his 

 work on a turtle, Clemmys c as pic a, in which a training technique was 

 used, with colored papers and colored lights as stimuli. As with the fishes, 

 intensity-discrimination appeared to be remarkably poor — the turtles 



