168 LESLIE B. AREY 



in which the optic nerve was cut. In such cases the rod never 

 elongated in the Hght although it often showed a tendency to 

 shorten when introduced into the dark, whereas the behavior 

 of the cone cells in light and darkness was the exact opposite 

 to that of the rod, since they tended to shorten in the hght but 

 remained unchanged in the dark. On these grounds, therefore, 

 an explanation is offered to show why it is that through the strong 

 stimulation produced by the direct action of light, both types 

 of cells show characteristic responses, while in the dark only 

 the more vigorous contractihty of the rod myoid becomes effec- 

 tive. It must be remembered, however, that although the direc- 

 tion of the movements of the rod and cone cells are opposed, 

 the real response of the protoplasmic myoid may be similar in 

 both cases. If this were true, the apparent inconsistency in 

 the movements of these elements would be due to a difference 

 in the axis of contractihty in the two kinds of myoids, and the 

 explanation just advanced would not stand. Reference will 

 be made to these possibilities in another place. 



b. Effect of temperature 



Previous attempts to determine the direct influence of tem- 

 perature upon the retinal elements have been confined to the frog. 

 Gradenigro ('85) found that if excised eyes of dark-adapted 

 animals were subjected to a temperature of 30° to 36°C. the 

 rods and cones shortened and the pigment expanded, both 

 end-results b^ng characteristic of light-adaption. Dittler ('07) 

 was able to confirm Gradenigro's discovery concerning the cone 

 cells. When the isolated retina was heated to 35° to 37°C. in 

 the dark for 50 to 60 minutes, the cone myoids shortened. After 

 retinas had been subjected to a temperature of 1° to 2°C, for 

 many hours, on the contrary, no shortening of the cone myoid 

 was observed. 



The apparatus and methods used by me were similar to those 

 described in connection with the experiments upon living fishes. 

 The excised eyes were contained in test tubes which were sus- 

 pended in jars of water kept at appropriate temperatures. Eyes 



