CHANGES IN RETINA OF EYES OF AMBLYSTOMA 75 



Changes in form and position of the rods have also been re- 

 ported. Angelucci ('94) found that the very large rods of 

 Salamandra clearly show a decrease in the length of the outer 

 segment after illumination. Garten ('07, p. 49) also observed 

 that the rods of the illuminated retina of the Salamander were 

 a little thicker and shorter. Van Genderen Stort ('87 a) has 

 further reported that in the dark eye of Triton the nuclei of the 

 rods extend over the external limiting membrane, resulting in 

 making the rod longer. In the light eye the rod nuclei are de- 

 scribed as all lying below the external limiting membrane. This 

 change in the position of the nuclei of the rods is supposed to be 

 brought about by the contractility of the connection between the 

 rod nucleus and the nuclei of the granular layer. Angelucci 

 ('94) reports the same thing as happen ng in the eye of Salaman- 

 dra maculata. Garten ('07, p. 21 and 50) was able to confirm 

 these observations for Triton (see his figs. 7 and 8) but owing 

 to variations in his results on Salamandra he leaves the matter 

 in doubt. 



ANATOMICAL FEATURES 



The larvae were exposed to light or darkness for varying 

 lengths of time. The entire animal was killed by throwing it 

 into sublimate-acetic. After being hardened in alcohol, the 

 upper jaw, containing the eye balls was cut off, and sectioned 

 after imbedding in paraffin or the piece contaning the eyes was 

 cut into two, right and left, parts and imbedded and cut sepa- 

 rately. The sections were 10 tx in thickness, and were stained in 

 eosin and toluidin blue, or in Ehrlich's hematoxylin and eosin. 



The visual cells of Amblystoma consist of both rods and cones 

 in the approximate proportion of 4:3. The most striking 

 thing about the rods is the short length of the 'myoid' and the 

 peculiar shape of the nuclei (see figs.). Instead of being round 

 or oval these nuclei are angular, and show an extension on the 

 internal side by means of the continuation of which the con- 

 nection between the nuclei and the internal granular layer is 

 effected. The external limiting membrane lies just below the 

 lower (internal) angles of the rod nuclei, so that the greater part 



