EFFECT OF LIGHT ON THE RETINA 



175 



The comparisons of light and dark eyes of Sceloporus show 

 that a pigment migration also takes place here. The average 

 of measurements indicate that the extent of this migration is 

 3.1m (table 2). 



TABLE 21 



1 Based on 10 measurements as in table I. 



Not only does the pigment migrate but the cones also show a 

 contraction in light. In table 1 the results of measurements 

 are shown. In the first place in the dark eye the distance 

 between the external limiting membrane and the choroidal edge 

 of the pigment epithelium is 5^ more than in the light eye. But 

 this does not represent the amount of contraction of the cones, 

 for as will be seen (column 2) the average length of the cones in 

 the dark eye is only 2.3fj, longer than in the light eye. From this 

 it is evident that the light not only causes a shortening of the 

 cones but a flattening of the pigment epithelial cells of, on the 

 average, 2.7^. 



This flattening of the epithelial cells in the tortoise retina is 

 in line with the results of others, x^ngelucci ('84 and '94) pointed 

 out that in the illuminated eye of the frog a shortening of the 

 epithelial cells in the direction of the axis of the rods was to be 

 observed. Chiarini ('04 and '06) also saw this change in the 

 retinal epithelial cells of the representatives of the five classes 

 of Vertebrates which he examined. And Pergens ('96) noted 

 the same thing in Leuciscus. 



In addition to this change in form of the epithelial cell there 

 has also been observed a change in the position of the nuclei of 

 these cells. Pergens ('96) found that after illumination the 

 nuclei of the pigment cells of Leuciscus were further forward 

 than in dark eyes. Angelucci ('94) also observed this change 

 of position in the frog. Garten ('07 b) on the other hand, al- 



