MOVEMENTS IN THE VISUAL CELLS 149 



that in fishes? The material, on which an answer to this ques- 

 tion was sought, was the larva of the bullfrog (R. catesbiana). 

 Animals were obtained during the month of April, 1914; these, 

 of course, represented larvae hibernated from the previous season, 

 since two or even three years are required to complete the meta- 

 morphosis of this species. A few experiments were also made 

 on animals obtained in November, 1914. 



From the larvae procured, two size limits were selected for 

 experimentation. The smallest larvae had a total body length 

 of 4.5 cm., the hind legs of such animals not being visible; the 

 largest larvae had a body length of 7.0 cm., and the hind 

 legs were developed as two small buds with the digits just 

 differentiated. 



In neither the 4.5 cm., nor the 7.0 cm. animals were the eyes 

 as deeply pigmented as in the adult of R. pipiens. Of the two 

 sizes, the 7.0 cm. larvae had the pigment more highly developed, 

 and consequently better differentiation was obtained at the 

 various temperatures with these, than with the smaller animals. 



The 4.5 cm. larvae at 3°, 26°, and 32°C. in the dark showed 

 the pigment in an expanded state (cf. figs. 20, 22) but not in a 

 firm zone of uniformly distributed granules. On the contrary, 

 the cells displayed pigmented processes that seemed to be more 

 or less independent of each other; the appearance of the zone 

 being that of a more uniform base with a fringe of pigment 

 extending distally from it. The degree of expansion at 2(3°C. was 

 distinctly less than at either 3°C. or 32°r., although at neither 

 of the extreme temperatures was the pigment as fully extended 

 as in the light. At 16°C\, however, a striking difTerence was 

 found (cf. fig. 21), for the pigment lay contracted in a narrow 

 compact layer near the choroid. 



The 7.0 cm. animals gave results (figs. 20, 21, 22) quite similar 

 to those just described, although the contrasts at the various 

 temperatures were considerabh' sharper due to the heavier pig- 

 mentation of the eyes at this stage. 



In these lar\'ae, therefore, the behavior of the retinal pigment 

 to temperature is identical wdth that characteristic of adult frogs. 

 Since these animals were always immersed in water, there is no 



