CHANGES IN RETINA OF EYES OF AMBLYSTOMA 77 



cones are slender and long and tapering, instead of roundly- 

 oval, and stain more intensively. They are to be seen in several 

 of the figures. 



EXPERIMENTAL 



Pigment migration. In a preliminary communication (Lau- 

 rens and Williams '16) it was stated that although there was a 

 decided forward movement of pigment when the eye was illumi- 

 nated, it was impossible to measure the extent of this move- 

 ment because of the fact that the distance from the external 

 limiting membrane to the nearest pigment needle, or from the 

 choroid edge of the epithelial cells to the farthest pigment 

 needle, is practically the same in both light and dark eyes. In 

 darkness, however, most of the pigment was found to be massed 

 near the base of the epithelial cells, while only a comparatively 

 small number of needles extended into the protoplasmic processes 

 between the visual cells. In light, on the other hand, a decid- 

 edly greater amount of pigment was found toward the external 

 limiting membrane resulting in the basal layer being thinner. 



As a result of further study involving the examination of 

 additional material it was found that this statement did not 

 altogether fit the case. In figures 1 and 2 a light and dark eye 

 are illustrated. A glance will show that these two figures, as far 

 as pigment position is concerned, do not represent a typical light 

 and dark eye respectively. For in the light eye the pigment is 

 actually more retracted than in the dark eye. Nevertheless 

 more pigment is forward in figure 1 (light eye) than in figure 2 

 (dark eye) although the basal layer of pigment in figure 2 (dark 

 eye) is hardly any thicker than in figure 1 (light eye). These 

 two figures represent extreme cases such as led us to the con- 

 clusions stated in our preliminary communication concerning 

 the inability of making measurements of the amount of migra- 

 tion. That figures 1 and 2 are really light and dark eyes respec- 

 tively is shown by the comparative lengths of the cone myoids. 



Figures 3 and 4 are two other figures of a light and dark eye 

 respectively. These are, in contradistinction to figures 1 and 

 2, characteristic of light and dark eyes in general as far as the 



