XVIII INSTINCTS AND TROPISMS 



347 



with their heads pointing toward the hght. The same 

 result occurred when the heat rays were ehminated by 

 passing the hght through a vessel of water before it entered 

 the box, showing that it was not the heat alone that caused 

 the frogs to retreat into the shade. If light be admitted 

 from below, which may be done by making the floor of the 

 box of glass, the frogs leap into the lighted area as before. 

 If the whole lower side of the box be exposed, the animal 

 takes a normal resting position, but if a half or two thirds of 

 it be covered, the frog moves toward the light and the 

 body assumes a greater angle to the horizontal, the angle 

 increasing, the smaller the area through which the light 

 enters. When light is thrown upon the frog from above, 

 the anterior part of the body becomes raised. Miss Torelle 

 found that when a frog was placed in a tall glass cylinder 

 the bottom and sides of which were covered with black 

 cloth, " the body was raised so that the fore legs were as 

 nearly as possible at right angles to the horizontal bottom 

 of the jar. This made the inclination of the body 60° or 

 over. Frequently the frog assumed an almost erect posi- 

 tion, by means of placing the fore feet against the side of 

 the jar." 



As these and other experiments show, the frog has a 

 strong tendency to place its body so as to face the light ; 

 yet notwithstanding its marked orienting response, it mani- 

 fests a strong proclivity to seek the shade. Frogs placed 

 out of doors, near the shadows of trees or buildings, soon 

 hop into the shade and remain there even if they have to 

 travel at right angles to the rays of light. Miss Torelle tried 

 the experiment of placing dark objects in the vicinity of the 

 frog to find if the animal showed any tendency to approach 

 them. " The side of a large wooden box was covered with 

 black cloth, and the frog placed near the black perpendicular 



