RESPONSES OF YOUNG TOADS 209 



would reach 6ne eye only with full effectiveness. Second, if 

 animals with image -forming eyes go toward a source of light, 

 because they perceive the light itself and follow it "much as 

 an animal pursues any other object of interest" as indicated 

 by Graber (I.e., p. 248), Torelle (I.e., p. 471), Holmes (1905a, 

 pp. 341, 344-345) and (1908, p. 496), and Mast (I.e., pp. 219, 223), 

 then such behavior may present a partial explanation as to the 

 reason why the toads used in Mast's experiments did not go 

 toward the stronger light, for the " attention " of the animals may 

 have been so fully occupied with the light in front of them that 

 they did not turn into the intersecting beam, and jump toward 

 the source of the stronger light. Further, it must be recalled, as 

 Mast (I.e., p. 223) himself has suggested, that the direction of 

 the rays in the field may be a guidance to the toads, especially 

 if they go toward an object because they see it. Then, the 

 after effects of the directive weaker light may have been suffi- 

 cient to keep the toads moving along the path already taken, 

 even when they reached the strong intersecting beam of light. 

 In so far as this work of Mast's applies to the writer's experi- 

 ments with young toads, certain facts should be kept clearly 

 in mind regarding the latter's experiments, that the animals 

 employed were extremely immature, that light approximating 

 10,000 ca.m. intensity was used, and that the toads reacted nega- 

 tively to the photic stimuli. From what is known of the habits 

 of toads, it was to be expected that the animals would respond 

 negatively to the strong stimuli from the projection lantern. 

 Toads are very largely nocturnal animals, and are more com- 

 monly seen about twilight when they leave their places of 

 "concealment," which they have occupied during the daytime. 

 The young toads respond positively to all the lesser light 

 intensities of white light. In these experiments it seems as if 

 the difference in the intensity of the stimuli on the two sides 

 of the body was an important factor in orientation. This sub- 

 ject has been discussed in connection with the responses to the 

 light from the projection lantern, and therefore will not be 

 dwelt upon here-. In jumping toward the light it is hardly prob- 

 able that the rays per se in the field are a very important ele- 

 ment in guiding the toads, for it has been stated that there 

 must be many cross lights in the field of experimentation. Of 

 course there is a certain part of Holmes's theory (1905, pp. 108- 



