266 



A. M. Banta 



5 mm. 10 mm. 15 mm. 



5.5 



ment, hence little photokinetic effect was to be inferred. The 

 reaction was clearly positive and continued positive until the 

 close of the experiment, although in another experiment the same 

 individuals following their exposure to diffuse daylight were nega- 

 tive to the same intensity of light. 



Two additional experiments are here given to show by contrast 

 the difference in the nature of the responses when the animals had 



previously been exposed to light 

 and when they had been in dark- 

 ness. December 12, 1905, 18 

 Asellus after exposure to diffuse 

 daylight were placed in the tank 

 and at once subjected to light 

 of 80 CM. intensity. Table V 

 and the continuous line in Fig. 

 4 show the results of this experi- 

 ment. 



The experiment was contin- 

 ued for only thirteen minutes; 

 the response was negative and 

 very marked. Many of the in- 

 dividuals started up rather 

 quickly, and all which responded 

 at once moved away from the 

 light. A little later two started 

 toward the light. By that time, 

 however, some had reached the 

 negative end and were turning 

 back. The record made at this 

 time — two minutes after the 

 start — shows the maximum re- 

 sponse, as judged by the change 

 in mean average position. It 

 will be seen that the photokinetic 

 Fi(. 4. Asellus communis (i8 individuals), gffect iu this experiment was 



Graphic representation of results of experi- 111 1 



_ , , • T ui V J ^7T Tj t very marked, but that, never- 



ments shown in Tables V and VI. Broken J ' ' 



lines based on Table VI. thelcss, the positive phototaxis 



