200 C. F. CURTIS RILEY 



in the experimentation dish that there was a tendency for some 

 of the toads to move into the spaces between the stones. The 

 writer has frequently observed a similar "habit" on the part 

 of mature and partially mature frogs. Large numbers of frogs, 

 chiefly Rana pipiens Schreber, were kept in two large tanks in 

 a basement room, the tanks being in diffuse daylight. It was 

 a very common sight to find as many as thirty individuals 

 crowded closely together in the angles formed by the sides 

 and bottom of each tank. Frequently they were congregated in 

 the more shaded corners, and the taking of such positions might 

 be due in part to a response to light. However, they were some- 

 times observed to be gathered in corners that were not so shaded. 

 At other times frogs were found to be grouped in the corners of 

 the tanks, both in shaded and unshaded situations. Not infre- 

 quently frogs were observed to be distributed sparsely about the 

 more central and open portions of the tanks. Such groupings as 

 have been described are in all probability due to responses to 

 contact stimuli. The movement into the shade may be due in 

 part to vision as Torelle (I.e., p. 470) has suggested. 



Other writers have recorded observations on the contact re- 

 sponses of toads and frogs. Torelle (I.e., p. 477) experimented 

 with specimens of Rana virescens virescens and Rana clamata in 

 a jar of water and found that the propensity of the frogs to 

 place themselves in contact with solid bodies "is apparently 

 stronger when the temperature is lowered." The following inter- 

 esting facts are quoted from the author's work cited above: 



"When a rock was lowered into the jar in such a way that a small space 

 was formed between it and the wall of the jar, the frog crawled into this 

 space and remained there. When a space was formed between the bottom 

 of the jar and the rock, it crawled into that. This was tested several 

 times, and was also observed when the temperature of the water in the 

 aquarium in which the frogs were kept was lowered 10° C. and below. 

 When this was done, all the frogs responded, either by flattening their 

 bodies against the stone floor, or by creeping under the rocks usually 

 kept there. It therefore seems that the frog is stereotropic in tempera- 

 tures between 10° C. and 4° C." 



These experiments of Torelle 's, considered with those (I.e., p. 

 476) on frogs out of water, seem to bear an interesting relation 

 to hibernation. It is probably true that this instinct is not 

 due to a single but to several causes. The increase of stereo- 

 tropism with a lowering of the temperature is an important 

 physiological change which may be related to the burrowing 



