RESPONSES OF YOUNG TOADS 211 



situation for some time, some of them climb up the perpendic- 

 ular glass wall at the end of the vessel. This places them out 

 of the most intense glare of the light. The young toads orient 

 promptly and definitely, by turning away from the source of 

 illumination and so place themselves that the longitudinal 

 axes of their bodies lie parallel with the incoming rays. This 

 position in relation to the rays of light is maintained while 

 traveling from one end of the dish to the other, and the pauses 

 between the jumps are brief, so that the animals move with a 

 fair degree of speed. The responses in water are similar to those 

 already described, the toads swimming away from the light. 



The young toads respond positively to the light from a 16 

 c.p. incandescent light, with an illumination approximately of 

 44 ca.m. They also respond in a similar manner to strong 

 diffuse daylight, to weak diffuse daylight, and to sunlight. Except 

 in the case of diffuse daylight, the animals jump toward the 

 source of illumination in a comparatively straight path. It 

 cannot be said that the median longitudinal axes of the bodies of 

 the toads are parallel with all the incoming rays, because many 

 of the rays enter the experimentation dish at various angles 

 and there must be cross lights within the field of experimenta- 

 tion. While the animals jump toward the light with consider- 

 able promptness, their motor responses are perhaps not so 

 quick as in the experiments with the projection lantern. At 

 times it seems as if the toads do not travel in quite so straight 

 a path as is the case when the intense artificial light is used as 

 a source of stimulation. The toads orient fairly definitely and 

 accurately, but not so promptly as when the projection lantern 

 is employed. At times, when responding to sunlight, the animals 

 come to rest in diffuse daylight, if it is nearby. Neither the 

 movement toward the light nor the orientation is so definite as 

 in the case of the stronger intensities. 



. It is not improbable that both light intensity and ray direc- 

 tion in the field are factors in these photic responses. During 

 orientation light intensity may play the more important role, 

 while the rays in the field may act as a guiding factor after 

 orientation is complete, though this does not necessarily do 

 away with the effect of intensity. In the positive responses 

 vision is an element not to be ignored, and it is probable that 



