178 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ently positive, and they tried for as much as five minutes to move 

 through a heat screen to the light. 



Six toads were next placed together in a rectangular glass vessel 

 (the floor of which measured twelve by twenty centimeters) and were 

 subjected to approximately the same light conditions as in the last 

 experiment. In jumping about they stimulated each other in a me- 

 chanical way. During fifteen minutes all the individuals remained 

 mostly facing the light and making vain attempts to reach it, and only 

 occasionally did one of them try to escape on the opposite side of 

 the jar. 



It is evident from these two experiments that mechanical stimulation 

 exerts an influence on the phototropism of the toad by enforcing the 

 effect of light, or, it could perhaps better be said, that the mechanical 

 stimulation furnishes the impulse to locomotion, while the light is 

 effective in determining the direction of the movement after locomotion 

 has been established. For the purpose of the present paper, however, 

 it makes no difference whether the responses obtained were due solely 

 to the influence of light or whether they were reactions to light after 

 mechanical stimulation. In either case the fact remains that both the 

 skin and eyes of amphibians act as photoreceptors, and that definite 

 reactions take place as a result of stimulation through either. 



C. The Reactions of the Toad to Photic Stimulation 



THROUGH THE EYES ALONE. 



Experiments have been described in this paper which show that 

 various amphibians react in the same way when either the skin alone 

 is stimulated or when both the skin and eyes are affected. The next 

 question which naturally arises is whether animals will react in the 

 same way when the stimulation is received through the eyes alone. 

 That such responses take place in Rana pipiens has been shown by 

 Parker (:03 b , p. 33), who found this species to be positively phototro- 

 pic when its entire surface was covered, with the exception of the eyes. 

 In order to test the toad in a similar manner the apparatus shown in 

 Figure 3 was used. Light was allowed to pass through a small open- 

 ing (e) in a screen, which could be adjusted so that only a small area 

 around the eye of the animal was illuminated. As an additional pre- 

 caution against light reception through the skin, the individuals used 

 were covered, except the eyes and feet, by a tight-fitting suit of soft 

 leather. As might be expected, the movements of the two animals 

 used in the experiments were slow. Each of these individuals was 

 placed with its right and left side alternately toward the light, the 



