78 VERTEBRATE PHOTORECEPTORS 



Among amphibians, cone movements were clearly dem- 

 onstrated in the frog by van Genderen Stort, and in the 

 toad by Arcoleo (1890). Responses of the salamander cones 

 were described by Angelucci (1894). His observations, how- 

 ever, were not supported by Garten (1907). In the eye of 



Fig. 57 (Left). Photomicrograph of depigmented Ught-adapted retina of 

 Ameiurus, showing contracted cones and elongated rods. X 305. 



Fig. 58 (Right). Photomicrograph of depigmented dark-adapted retina of 

 Ameiurus, showing elongated cones and contracted rods. X 305. 



larval Amblystoma, definite cone responses have been noted 

 (Detwiler, 19236). 



In reptiles possessing cones only, the results have been 

 inconsistent. Slight changes have been reported by Chiarini 

 (1906), and by Garten (1907) for the rodless retinas of Hzards 

 and the chameleon. The author also observed detectable 

 cone contraction in turtles and lizards (Detwiler, 1916, 

 1923a, 1923c). 



In birds, it has been possible to compare the movements 

 of the cones in regions with many rods (yellow field), few 

 rods (red field), and none at all (fovea). As measured from 

 van Genderen Stort 's (1887) plates, Arey (1928) expresses 

 the relative changes in length as follows : — fovea : red field : 

 yellow field = 23 : 32 : 40. Garten (op. cit.) substantiated 

 this relationship and also extended his observations to the 



