202 



CHARLES HARLAN ABBOTT 



12.79 CM. for the central point, made six weeks after the read- 

 ing of 12.955 CM. recorded in figure 3. 



It can be seen from figure 3 that an animal starting from the 

 central point will go into a region of diminished intensity unless 

 it travels into the quadrant of the circle toward the source of 



Direcition of 

 Light 



97.28 



9.7,45 



4.92__ 

 12.955__- 



5.945 



4.205 



_2.93. 



Fig. 3 Diagram of experimental field, showing intensities of light in CM. 

 at principal points of the field, measured with Macbeth illuminometer. Heavy 

 black line shows the division of the circle into two parts, negative and positive. 



light. This fact makes possible a division of the circle into the 

 tw^o parts shown in figure 3. If the animal leaves the circle in 

 the quadrant nearest the light, it goes into a region of increased 

 illumination, and hence shows a positive response. If it goes in 

 any other direction, the response is negative. 



