162 LESLIE B. AREY 



I was unable to discover constant differences in length that 

 could be correlated with definite temperatures. The agreement 

 of mean values obtained from various retinas under identical 

 temperature conditions was not good, and since the rod myoid 

 measures only 6 yu to 12 /i in length, even small variations fur- 

 nish serious obstacles in determinations of this kind. In any 

 one preparation, moreover, variability in the length of adjacent 

 myoids tended somewhat to mask a possible temperature effect. 

 If anything, my measurements showed the reverse of what 

 Gradenigro maintained, the elongation at 33°C. in the dark 

 being greater than at 5°C., but, as stated before, these results 

 are by no means trustworthy. 



A shortening of the rod through the action of high tempera- 

 ture, as claimed by Gradenigro, is of interest because, accord- 

 ing to most investigators, light produces the same result. With 

 this can be compared an analogous correlation in fishes, where 

 light causes an elongation of the rod myoid and, as I have shown, 

 elevated temperature does likewise. It is certain, on the con- 

 trary, that although the cones of both frogs and fishes shorten 

 in the light, heating produces unlike responses in the dark, 



(2) Rana catesbiana (larvae). Although the cones in both 

 the 4.5 cm. and the 7.0 cm. larva of this frog are of large size, 

 clearly defined temperature responses were not observed; in- 

 deed, the difference between the positions assumed even in light 

 and darkness is not striking, the cone myoids in the light re- 

 maining well elongated in comparison to those of the adult R. 

 pipiens. The variability in length in different preparations is 

 considerable, yet if anything, the cones appeared more shortened 

 at 3°C. than at higher temperatures. There is no marked shorten- 

 ing at 33°C., for the cones under these conditions were as long 

 as at lower temperatures, and in some cases longer. It is 

 probable that the responses of the cones in adult R. catesbiana 

 will be found to agree with those in other species which have been 

 studied, although no experimentation was performed to deter- 

 mine this point. 



3. Necturus. The rods, and the single and double cones of Nec- 

 turus are very large, yet positional changes with varying tempera- 



