1 74 'Journal of Comparative Neurology and Psychology. 



made to fit the groove represented at the middle of the ends of the 

 aquarium, Fig. 15, a. The colonies in each half were then 

 counted and the numbers recorded. The aquarium could be 

 moved to the right or left along the metric gauge and in this way 

 the intensity of the light entering opposite sides of the aquarium 

 could be regulated. The candle power of the glower and the 

 distances between it and each side of the aquarium being known, 

 the difference in light intensity on opposite sides of any object in 

 the middle of the aquarium could easily be calculated. 



TABLE V. 



Distance from glower to center of gauge loo cm. Light intensity 27 candle meters. 



