254 ^- ^- Banta 



8:15 9:15 10:15 11:15 12:15 1:15 2:15 3:15 4:15 



3.5 



4.5 



^ 



Fig. 2. Asellus communis (25 individuals); Jan. it;, 1907; previous exposure, difiFuse 

 daylight; illumination horizontal, i. C. M. 



average positions at the different epochs at which records were 

 made was used, e.g., getting the mean average position for the 

 period ending at 8:30 the average of the mean average positions 

 for 8:14, 8:18, 8:20. and 8:30 was used. The base (heavy) hne 

 represents the middle of the tank. Points above the hne indicate 

 mean average position nearer the positive end of the tank and 

 points below the base hne indicate mean average position nearer 

 the negative end of tank. In this experiment Asellus showed no 

 response to the light stimulation. The mean average positions 

 varied from a maximum of 4:56 at the start to a minimum of 4:16 

 at 3:38 o'clock, but at the close of the experiment, nearly 8 hours 

 after the start, it was 4.40. Hence the change in mean average 

 position from the beginning to the close of the experiment was only 

 + 0.16. In view of the fact that when a definite light response is 

 obtained with Asellus it is quite pronounced, this slight change in 

 position is of no significance. 



Numerous experiments were made upon Asellus with horizontal 

 illumination at intensities ranging between o.ooi CM. and i.o 

 CM.; the mean average position was as often changed in a nega- 

 tive as in a positive direction. This change was never sufficient 



