376 



LESLIE B. AREY 



necessary for dark-adaption, whereas a much shorter time 

 (approximately I5 hours) suffices for light-adaption. Hess's 

 results upon Octopus defilippi (one of the several species studied 

 by him) are especially astonishing, since he states that dark- 

 adaption occurs in 48 hours, whereas light-adaption may be 

 practically c()]n])lotod in 15 minutes. 



(c) Effect of temperature 



Next to light, temperature is the commonest environmental 

 stimulating agent that controls the movement of retinal pig- 

 ment. Accordingly, a series of tests were made, both on nor- 

 mal and excised eyes, to discover whether a correlative tempera- 

 ture response is demonstrable. 



Measurements showing the relative distribution of pigment in the eyes of Planorbis at 

 3° and 32°C. both in darkness and in light. The values are mean values expressed 

 in micra and indicate both the thickness of the main pigment mass (zonal meas- 

 urement), and the zonal measurement plus the length of the pigmented processes 

 (process measurement). Corresponding values at room temperature, copied 

 from Table 1, are given in parenthesis 



CONDITION OF ILLUMINATION 



MEAN 



PROCESS 

 MEASUREMENT 



Light.... 

 Light.... 

 Darkness 

 Darkness 



10.0 



14.0 



(11.0) 



(16.5) 



12.5 



19.0 



13.0 



19.0 



(18.0) 



(25.0) 



14.0 



24.0 



1. Effect on normal animals. Fully light- and dark-adapted 

 snails, retained in jars of water, were each subjected to tem- 

 peratures of approximately 3° and 32° C. At the end of 4 hours 

 the eyes were fixed at temperatures identical with those at 

 which the respective experiments had been conducted. The 

 data from these determinations are presented in table 3. 



These data show that temperature is extremely efficacious 

 in evoking positional changes in the retinal pigment. Since, 



