170 LESLIE B. AREY 



to temperatures of 3°, 16°, and 33°C., but no changes were ob- 

 served in the position of the retinal pigment. These results, 

 which do not agree with Gradenigro's statement, by no means 

 furnish conclusive proof that in the Hving frog temperature 

 operates through the nervous system, yet when supported by a 

 comparative study of the retinal pigment and melanophores of 

 other animals, the conclusion reached by Herzog ('05), that the 

 expansion of the frog's retinal pigment under these circumstances 

 is of nervous origin, involving the principle of specific energies, 

 becomes highly probable. 



According to Fujita ('11), when excised eyes from dark-adapted 

 frogs are retained in the dark for 20 minutes, the pigment assumes 

 a partial light position. My observations do not confirm this 

 result, for no migration of any consequence occurred. 



2. Effect of temperature upon visual cells. When a study of 

 the visual cells of Ameiurus was made, the effect of temperature 

 was found to be essentially similar to that upon normal animals. 



WTien eyes from dark-adapted individuals of Abramis that 

 had previousl}^ been kept at a temperature of 25°C. were like- 

 wise excised and subjected to 5°C. and 25°C. in the dark, 

 those at 25°C. (fig. 27) retained the elongated position while 

 those at 5°C. (fig. 25) shortened to a considerable extent 

 although somewhat less than in living animals. Mention has 

 already been made of the significance of these results in con- 

 nection with the applicability of Dittler's theory of chemical 

 stimulation to the cones of fishes. Although the rods of Abramis 

 at both temperatures showed a distribution extending over wide 

 limits, yet the shortest measured 12 /x at 5°C. as compared with 

 20 n at 25°C., and the modal elongation at the same temperatures, 

 as judged by the eye, was 18 m and 25 ^ respectively. It is 

 interesting to note that in the excised eyes of dark-adapted 

 Abramis, temperature is able to produce changes in both the 

 retinal pigment and visual cells, notwithstanding the fact that 

 light and darkness are wholly ineffectual in this respect. 



Table 11 summarizes these results from typical retinas. 



A few experiments were performed upon the cone cells of 

 the frog. The results obtained were identical with those stated 



