174 



S. R. DETWILER 





® 





Fig. 1 A portion of the retina of Chrysemys picta. Animal kept in darkness 

 for 24 hours. 



Fig. 2 A portion of the retina of Chrysemys picta. Animal, after having 

 been kept in darkness for 24 hours, placed in sunlight for 6 hours. N? 



Fig. 3 A portion of the retina of Chrysemys. From an individual with cut 

 optic nerve, kept in darkness for 24 hours, followed by a 7 hour exposure to 

 sunlight. 



Fig. 4 A portion of the retina of Chrysemys. From an individual with cut 

 optic nerve and kept in darkness for 24 hours. 



All of the figures were drawn with the aid of the camera lucida, and with Leitz 

 oil immersion tV objective and ocular 4, giving an approximate magnification of 

 1340 diameters. The figures were then reduced § for publication so that as 

 they appear they have a magnification of about 890 diameters. 



All of the drawings were made at about 1 mm. distance from the entrance of 

 the optic nerve. 



