MOVEMENTS IN THE VISUAL CELLS 151 



the contraction in the dark in hi.s study of visual cells. This 

 situation is comparable to that found in Triton where movements 

 of the pigment through the influence of light were discovered 

 by Angelucci (78), Stort ('87) and Garten ('07). The extent 

 of pigment migration in this animal is described as being very 

 limited by Garten (p. 70) who says: ". . . . diesclbe ist 

 aber hier unvergleichlich viel schwacher als bei vielen andereii 

 niederen Wirbelthieren." 



In an examination of the effects of various temperatures 

 on dark-adapted eyes, however, no constant differences were 

 noted. In some instances the processes of the cells seemed to 

 be less heavily pigmented and the bases more heavily pigmented 

 at 15°C, than at the two extreme temperatures, but this was by 

 no means constant. At least, it can be said that there is no 

 marked contraction of the pigment in the dark at any temperature. 



The evidence from Xecturus and the limited pigment migration 

 in Triton conclusively prove that the pigment responses typical 

 of the frog are not common to all amphibians. It is probable, 

 therefore, that such peculiarities as were described for the frog 

 have been developed solely within the anuran group. 



b. Vi^sual cells 



Although the myoids of both th(^ rod and cone cells of fishes 

 are capable of a high degree of contractility (a 90 per cent re- 

 traction occurs in some instances) , the effect of various tempera- 

 tures on these cells remains untried up to the present time; in 

 fact, the frog is the only animal upon which such work has been 

 attempted. CJradenigro ('85), Angelucci ('S4b), Herzog ('05), 

 and P'ujita ('11) found that warming produces the same effect 

 on the cones of the frog as does light. Herzog also stated that 

 coohng to 0°C. Hkewise caused the cones to shorten, although 

 Fujita denies that this occurs. 



There is no record of any attempt to determine the effect of 

 temperature upon the rods of vertebrates beyond the statement 

 of Gradenigro ('85) that at 30°C. the rod of the frog shortens 

 as in light. 



