CHANGES IN THE VISUAL CELLS OF THE FROG 441 



ance of these elements in his own sectioned material was dis- 

 similar. In the figures corresponding to the text descriptions 

 of dark-adapted rods (the figures and their appended descriptions 

 are apparently interchanged in his paper), the varicose outer 

 members are t\\dce, and the ellipsoids three to four times, as 

 broad as the corresponding parts of the light-adapted rods. 



My observations, therefore, are opposed both to those of 

 Lederer ('08) who believed that darkness causes the rod to 

 swell, and to those of Ewald and Kiihne ('78), who recorded 

 that light acts in this manner. 



SUMMARY 



1. Distinct movements of the nuclei of the red rod-visual cells, 

 due to photic stimulation, are not demonstrable. Hence move- 

 ments of the rods are not produced indirectly in this way. 



2. The myoid of the rod-visual cell elongates in light and 

 shortens in darkness. Therefore, contrary to the conclusions of 

 the older workers, the photomechanical response of the frog's rod 

 myoid is found to be similar to that occurring in the retinas of 

 all other investigated vertebrates. 



The mean length of aj^proximately 1000 myoids from 23 

 light-adapted retinas is ll.G m- 



The mean length of approximately 1000 myoids from 23 dark- 

 adapted retinas is 5.9 fx. 



3. A significant regional difference in the length of the red- 

 visual rod myoid is not api^arent from comparisons of approxi- 

 mately 2000 measurements made at the center and the periphery 

 of light- and dark-adapted retinas. 



4. The myoid of the green visual rod probably elongates 

 slightly in the light and shortens in darkness. 



The mean length of 100 myoids from 10 light-adapted retinas 

 is 27.7 fji. 



The mean length of 100 myoids from 10 dark-adapted retinas 

 is 24.4 fjL. 



5. Definite changes in the diameter of the outer member, or 

 of the ellipsoid, of the red visual-rod can not be correlated with 

 photic influences. The rod mj^oid, however, does become 

 tenuous in the light. 



