CHANGES IN THE VISUAL CELLS OF THE FROG 



439 



furthermore, made use of these data in an argument against the 

 feasibihty of attempting to advance (in the hght of our present 

 knowledge)' a single rational explanation for the diverse photo- 

 mechanical movements of the \dsual rods. It is evident, how- 

 ever, that the conclusion reached in the present investigation 

 renders this particular objection invalid. 



It is reasonable to expect, although material is not available 

 at present to put the matter to an experimental test, that the 

 photomechanical behavior of the toad's visual rod will be found 

 to vary in no essential detail from that herein described for the 

 frog. 



b. Green rods. From the sixty retinas experimented upon, 

 the ten light-adapted and ten dark-adapted preparations which 

 showed the most perfect histological preservation were selected 

 for measurement. In each retina, measurements were made of 

 the myoid length (figs. 1 and 2, my.bac.vr.) of ten consecutively- 

 placed green rods; the results are recorded in tables 3 and 4. 



TABLE 3 

 Measurements from ten dark-adapted retinas of Rana pipiens. The values arc in 

 micra and represent measurements taken along axes eoinciding tcith radii of the 

 eyeball. Each value for the length of the green rod myoid is the mean obtained 

 from ten consecutively-placed elements 



membrane, although nothing to this effect is stated Furthermore, the varicose 

 and atypical appearing rods naturally increases one's caution in accepting his 

 conclusions. Although Loderer gave but little emphasis to his observations 

 on sectioned material (p. 431). I believe that those observations constitute the 

 strongest evidence in support of his thesis. 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 



