184 C. F. CURTIS RILEY 



difference in these results from those of Pearse is probably due 

 to the fact that the writer employed more powerful stimuli in 

 his experiments. Further, the writer used animals of much 

 greater immaturity than was the case in Pearse 's experiments. 



III. RESPONSE TO LESS INTENSE ARTIFICIAL LIGHT 



The young toads are next subjected to light of much lower 

 intensity. The vessel containing the animals is placed directly 

 in front of the bulb of an ordinary 16 c.p. incandescent electric 

 light. Within the field of experimentation the illumination is 

 approximately 44 ca.m. The first noticeable movement is the 

 orienting response, all the toads so placing themselves, with 

 respect to the light, that the longitudinal axes of their bodies 

 become parallel with the longitudinal axis of the dish, which 

 points directly toward the light. This response brings the 

 toads into such a position that their heads are turned directly 

 toward the source of illumination, and the median longitudinal 

 axes of their bodies lie parallel with many of the rays passing 

 through the bulb. However, with a light of this nature, it is 

 incorrect to state, without qualification, that the median longi- 

 tudinal axis of the body is parallel with the rays of light. Im- 

 mediately after completing orientation, the toads jump in the 

 direction of the light until they all reach the extremity of the 

 vessel nearest to the source of illumination. The organisms 

 remain oriented while traveling from one end of the glass trough 

 to the other. Parker (I.e.) found that Rana pipiens Schreber 

 oriented itself with its head ■ toward the light and also moved 

 toward the source of illumination. These were the responses 

 to the intermediate light intensities between 1 and 20,480 ca.m. 

 After the young toads had all reached the end of the vessel, 

 it is turned around until the animals are moved to a position 

 farthest from the source of light. They quickly perform the 

 orienting response and again jump away toward the light. In 

 this manner the animals are driven repeatedly from one end of 

 the dish to the other. Usually, orientation is not performed so 

 promptly nor do the toads jump so rapidly as in those experi- 

 ments with the projection lantern. When the animals reach 

 the end of the trough, they frequently climb up the end wall 

 of the vessel as if to move still nearer to the source of illumina- 

 tion. There is no definite evidence that the median longitu- 



