MOVEMENTS IN THE VISUAL CELLS 185 



redistribution of pigment than is low temperature. The results 

 obtained from the four fishes studied indicate that extreme 

 conditions both of expansion and of contraction are not to be 

 found in the retinal pigment of any one fish. 



3. In darkness, the retinal pigment of the frog undergoes 

 striking expansion l)etween the temperatures of 0° to 14°C. 

 and 19° to 33°C., whereas at the intermediate temperatures of 

 14° to 19°C. it is highly contracted. Temperature is without 

 effect upon light-adapted retinas. Shice the retinal pigment 

 of the larvae of Ran a catesbiana shows temperature responses 

 identical with those characteristic of adults, there is no tem- 

 porary- lar^'al recapitulation of the responses characteristic of 

 fishes. 



4. Light and darkness protluce but limited changes in the 

 distribution of the retinal pigment of Necturus. No definite 

 effect of temperature could be detected. It is ])robable that the 

 peculiar res])onses found in the frog have been developed within 

 the anuran grou]). 



5. The cone inyoids ot' fishes sjiortcn at low temperatures in 

 the dark: at liigh temperatures they lengtlieu. Not only is 

 elongation i)rogressive, extreme conditions Ix'ing found at 0° 

 and 30° ± C, but also the rate of change is directly proportional 

 to the tem])evature gradient. Tem])erature is iiieffectual in 

 the light. 



(). The myoid of the rods of fishes also elongates at high tem- 

 ])eratures and shortens at low temjieratures, but the extent of 

 change is mucli less than that of cone cells. 



7. The cone myoiil of adult frogs in the dark shortens when 

 subjected to a temperature of 19° to 33°C., but remains 

 elongated at all lower temperatures. Xo definite temperature 

 responses of the cone myoids were found in the larwae of 

 Rana catesbiana. 



8. A correlation between the length of the rotl myoid and 

 temperature was not detected in the frog either in darkness 

 or in light. 



9. The positions of the visual cells of Necturus are not affected 

 by temperatures l)etween the limits of 0° and 28°C. 



THE JOIRNAL OF CO.MP A HATI \ E NEUKOI.OOY. \ OI.. 2<i, NO. 2 



