186 



ADAPTATIONS TO DIURNAL ACTIVITY 



been in agreement that this snake has the sharpest sight and the most 

 accurate judgment of distance of any in the world. A very similar situa- 

 tion obtains in the African bird snake, Thelotornis ktrtlandi; and prob- 

 ably also in Dryophiops, whose pupil is similar. 



a in turtles. 



sagittal section of retina through the area centralis of the western painted turtle, Chrys- 

 emys picta marginata. The optic nerve head is out of the picture a bit to the right, 

 b, section of retina through the fovea of a soft-shell turtle, Amyda sp. Redrawn from Gillett. 



pe- pigment epithelium; r- receptor layer; /- limitans; on- outer nuclear layer; op- outer 



plexiform layer; in- inner nuclear layer; ip- inner plexiform layer; g- ganglion layer; n- 



nerve fiber layer. 



Fig. 79 — The East Indian long-nosed tree-snake, Dryophis mycterizans. 



a, right eye in situ, from the side, showing aphakic portion of pupil and cheek groove which 

 permits straight-forward vision, x 4. From alcoholic specimen, as- aphakic space; /- lens; 

 g- groove, b, face, showing provisions for binocular vision, x 2. From Franz, after Beer, 

 c, anterior segment of right eye, showing form of iris, lens, and aphakic space, x 4. From 

 Franz, after Beer, d, head from above, cut away to reveal eye in section, showing line of 

 sight from temporal fovea through lens and aphakic portion of pupil and along cheek 

 groove, x 2. From alcoholic specimen and microscopic preparations. 



