348 THE BIOLOGY OF THE FROG chap. 



surface. It hopped close to this, remained a couple of 

 minutes, then moved close to the wall of the gray-colored 

 building, where it remained at rest in the angle formed by 

 the wall and the ground. When placed near the uncov- 

 ered box (pine) on the side in full sunlight, there was no 

 movement toward it. When the box was raised on one 

 edge and propped, so that the other edge was about four 

 inches from the ground, the frog moved toward the shadow 

 thus formed, crept well under the box, placed its body be- 

 tween the floor and the ground, where it remained with its 

 head directed outward. A black cloth was fastened close 

 to the ground in the center of a sun-illuminated area, and a 

 frog placed near it moved on to it, crept along the edge 

 as if seeking cover, then hopped off. A second frog also 

 hopped on to the cloth, but almost immediately moved off. 

 Apparently a dark surface, brightly illuminated, does not 

 produce the effect of a shadow or of diffuse light." It may 

 be, however, that frogs are attracted to such surfaces just 

 as they are to shadows, but finding different conditions of 

 stimulation when they get there they do not remain. 



It is clear that the frog manifests two quite different 

 responses in its behavior toward light. The orienting 

 response, in which the animal puts itself in line with the 

 direction of the rays, affords a good illustration of photo- 

 taxis. The proclivity to seek and rest in the shade is more 

 nearly akin to what is commonly called photopathy. Under 

 ordinary conditions the frog may be considered as positively 

 phototactic, but negatively photopathic. . Many animals col- 

 lect in the shade, not because they are negatively photo- 

 tactic, but because when they happen to reach the shade in 

 the course of their moving about, they come to rest there. 

 The collection of frogs in shady spots may be partly ex- 

 plained in this way, but there appears to be also a percep- 



