RESPONSES OF YOUNG TOADS 199 



ber of young toads in the experimentation dish at the same 

 time. Occasionally in jumping toward or away from the source 

 of illumination two individuals come in contact with each other. 

 Frequently this contact appears to have no effect upon the 

 animals so far as their response to light is concerned. At other 

 times one or both of the toads pause for a few seconds before 

 again reacting with the motor response with reference to the 

 light. Generally, however, when contact occurs it seems to act 

 as a stimulus in inducing the motor response. This is noticeable 

 when a toad, in jumping, comes in contact with a stationary 

 individual, the latter's motor response being invoked. If a 

 toad does not respond to the light for a few seconds, but remains 

 quietly resting in one position, and if then it is stimulated by 

 means of another animal jumping against it, the motor response 

 may result and this may be followed by the animal responding 

 to the photic stimuli. These statements apply more largely 

 to the experiments with the weaker intensities. Parker (I.e., 

 pp. 28, 29) found when subjecting frogs, Rana pipiens Schreber, 

 to the lower light intensities from a Nernst glower that, 



" In some instances after a frog had remained ten minutes or more 

 without changing its original position, it was induced to jump by being 

 touched from behind, and, when this was done, the animal almost invari- 

 ably turned first and then jumped toward the source of light." 



Pearse (l.c 7 pp. 177, 178) in discussing "the influence of 

 mechanical stimulation on the photic reactions of the toad," 

 Bufo americanus and Bufo fowleri, when subjected to a light 

 intensity of 220 ca.m. states that, 



"In jumping about they stimulated each other in a mechanical way. 

 * * * It is evident * * * 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 fur- 

 nishes the impulse to locomotion, while the light is effective in determining 

 the direction of the movement after locomotion has been established." 



The writer has noticed in his experiments with the less intense 

 illuminations that when several young toads move into the angles 

 formed by the bottom and sides of the experimentation dish 

 that the contact of their bodies and of the solid surfaces of the 

 vessel seem to inhibit the motor response for some time. The 

 animals remain quietly resting with their bodies in rather close 

 contact. During the experiments with weak diffuse daylight, it 

 was found that when stones were placed about 25 mm. apart 



