EFFECT OF LIGHT ON THE KETINA 167 



23-30m. Finally Garten ('07, p. 25) found also a very slight 

 contraction (not more than 1.1 ix) in the eye of Chameleon. 



From this brief review of the few papers on the subject con- 

 cerning reptiles we see that pigment migration and cone con- 

 traction are very slight if they occur at all. No work of this 

 nature has been carried out on American species, and since it is 

 desired to carry out a series of further experiments on tortoises 

 and lizards with particular reference to vision, it was thought 

 that something should be known concerning the reactions of 

 the various parts of their retinae to light. Three species of 

 tortoises and one of lizards were used in the present investiga- 

 tion, viz., Chelopus guttatus, Chelopus insculptus, Chrysemys 

 picta, and the common southern fence lizard, Sceloporus undu- 

 latus. Most of the work was carried out on Chrysemys and 

 Sceloporus. 



This investigation was taken up at the suggestion of Dr. Henry 

 Laurens. It gives me pleasure to express here my thanks to 

 Dr. Laurens for the assistance that he has given me during its 

 completion. 



METHODS 



The methods of exposing the animals to light and to darkness 

 were as follows: Two active animals were selected and placed 

 in darkness for 24 hours. At the end of that time one of them 

 was taken from the dark room and placed in direct sunlight for 

 at least 6 hours after which it was killed. The other animal 

 was either killed after it had been in darkness for 24 hours or 

 after it had remained there at least 6 hours more. The eyes 

 were removed as quickly as possible after the animals had been 

 killed by decapitation — the dark eyes under red light, the light 

 eyes in sunlight — and immediately dropped into the fixing fluid. 

 The time consumed between decapitation and fixation was 5 

 minutes or less. 



The fixation and subsequent procedure which gave the best 

 results was the following: Fixation in Kleinenberg's strong picro- 

 sulphuric for 4 to 5 hours, followed by 70 per cent alcohol, which 

 was frequently changed and in which the eyes were allowed to 



