Reactions of I so pods to Light 



253 



TABLE I 



AsELLUs COMMUNIS (25 individuals) 

 January 15, 1907 

 Illumination: horizontal, I CM.; lamp placed at Section-I end 

 Previous exposure: disuse daylight 



observation, the eighth column gives the mean average position 

 at each epoch and finally, at the bottom of the last column, the 

 change in the mean average position between the first and the last 

 observation. The mean average position was calculated by multi- 

 plying the number of each section of the tank by the number of 

 individuals in that section and dividing the sum of these products 

 by the whole number of individuals. 



The results of this experiment are graphically represented in Fig. 

 2, which shows a curve constructed by using the mean average 

 positions as ordinates and the fifteen minute periods of the experi- 

 ment as abscissas. 



For convenience not more than one ordinate was used for each 

 fifteen minute period of the experiment. If more than one record 

 had been made during the fifteen minutes, the average of the mean 



