434 JOHN B. WATSON 



suits seem to show such a relation between human vision and 

 reptilian vision. 



Hess believes, from a histological examination of the eyes 

 of both the hen and the turtle, that the reason for the narrowing 

 of the spectrum at the short end is to be found solely in the 

 physical fact that the recipient retinal elements in the one 

 case are placed behind a film composed of red and yellow oil 

 particles (turtles), and in the other, behind one composed of 

 yellow and green particles (hen). 



His work upon amphibians is merely summarized. He found 

 Diemictylus viridescens, Biifo vulgaris and Xenophus Mulleri 

 most suitable subjects. All three forms possess retinae liberally 

 supplied with rods. The course of adaptation to white light 

 in the salamander, Diemictylus viridescens, was almost exactly 

 identical with that in the human eye. There was no narrowing 

 of the spectrum at the short end, as is the case in reptiles and 

 birds. There is no shortening in the red. They are able to 

 see the food in the blue-green and in the red region as long as 

 can the human eye in a similar state of adaptation. 



The paper has important bearing upon theories of color vision. 

 We have a clear proof of the functioning of a light-adaptation 

 mechanism for both mixed and monochromatic light in a retina 

 which is totally unsupplied with rods and hence with visual 

 purple. 



Pearse "\ in a closely articulated paper, too extended for 

 review, gives in addition to a good historical survey of the work 

 of other investigators, an account of several experiments upon 

 light and heat responses of different amphibians. 'After giving 

 a long list of the forms positively phototropic, he states among 

 his conclusions that most of the species mentioned in the list 

 gave normal photic responses after removal of the eyes and 

 that the responses in these eyeless animals are due to the fact 

 that the skin functions as a photoreceptor. Blue light was 

 most effective in the production of the tropic responses in normal 

 animals. But when eyeless individuals were tested with the 

 same colored lights the rays toward the blue end showed no 

 such potency as compared with those nearer the opposite end. 

 He concludes that while both the skin and the eyes are sen- 

 sitive to the whole range of the visible spectrum, color sensitive- 

 ness is present only in the latter. Spinal amphibians gave no 



