144 LESLIE B. AREY 



point was desired, the outer chamber of the tank was filled with 

 a mixture of ice and water; if a sufficient amount of ice was 

 provided a temperature of from 3° to 5°C, could be maintained, 

 without further attention, throughout the whole experiment. 

 At the expiration of the time allowed for temperature adaption 

 (usually 3 hours), the apparatus was placed in the dark or in 

 weak red light and the frog's eyes were removed and fixed in 

 darkness at the same temperature as that at which the experiment 

 had been conducted. 



In the course of these tests nearly 100 eyes were examined, 

 yet the general results obtained were identical with those de- 

 scribed by Herzog. At 3°C. and 33°C. (figs. 17, 19) the pig- 

 ment was expanded approximating the condition characteristic of 

 light; between the temperatures of 14°C. and 19°C. (fig. 18), 

 however, the pigment was contracted to a narrow compact layer. 

 It should be noted that 14°C. and 19°C. may not represent the 

 limiting temperature at which pigment contraction occurs, 

 although Herzog states this to be the case; no attempt was 

 made by me to determine these intermediate temperature-limits. 

 At low temperatures the expansion of pigment was generally 

 not as complete as at a high temperature or in the light, and there 

 was often considerable variation in different parts of the same 

 retina, yet the general result was one of unmistakable expansion. 



In some cases, however, there was little or no evidence of a 

 pigment expansion at the lower temperature, yet such instances 

 were comparatively rare. Although the cause of discrepant 

 results of this kind is not evident, they perhaps furnish additional 

 proof for the nervous control of the frog's retinal pigment, as 

 many workers maintain {vide infra). It seems probable that 

 Fujita was unfortunate enough, in the few experiments which 

 he performed at a low temperature, to obtain nothing but this 

 lack of typical results, although in my own work the occurrence 

 of such anomalous cases was always sporadic. 



A careful comparison was made of the results obtained at 3°C. 

 and 33°C. No constant difference in the amount of migration 

 could be detected, although Herzog states that at 37°C. the 

 distal migration is greater than that obtained at low temperature. 



