268 A. M. Banta 



The response was somewhat less prompt in the second experi- 

 ment, but it was as definitely positive as the response in the first 

 experiment was negative. 



Numerous experiments were also made with other intensities 

 (3 CM., II CM., and 25 CM.). The results support the con- 

 clusion that Asellus after being kept in the dark is positive to all 

 intensities of light between 2.5 CM. and 80 CM. Some of these 

 experiments were continued for periods varying from 3 to 5 hours 

 and the positive response persisted throughout the whole time. 

 The maximum response, however, usually occurred between 30 

 and 90 minutes after the experiments began. When Asellus was 

 subjected to a light intensity of as much as 2855 CM. the animals 

 very soon sought the negative end of the tank, although for a 

 short time the response was often positive. These experiments 

 indicate that after retention in darkness Asellus is positive even 

 to light of fairly high intensities, but that with intensities as high 

 as 2855 CM. it very soon becomes negative. 



From the foregoing experiments with Asellus when subjected 

 to horizontal illumination of various intensities, after being in 

 darkness, these conclusions have been reached: 



1 Asellus does not respond to intensities of i CM. or less. 



2 It does respond to intensities from 2.5 CM. to 2855 CM. 



3 This response is largely a direct phototactic effect, since the 

 animals before exposure to specific intensities of light had been 

 retained in darkness in the tank and of course had become thor- 

 oughly settled there; but the photokinetic element is also recog- 

 nizable. 



4 The immediate response to intensities from 2.5 CM. to 

 80 CM. is positive and continues to be so for at least 3 to 5 hours. 



5 With an intensity of 2855 CM. the response is often posi- 

 tive at first, but soon becomes negative. 



By way of a general summary of the effect of horizontal illu- 

 mination upon Asellus, it may be said, thatafter exposure to diffuse 

 daylight it is negative to all intensities greater than about 2 CM. 

 It does not respond to lower intensities. Light has both a pho- 

 tokinetic and phototactic effect upon Asellus. The photokinetic 

 effect is often sufficient to mask for a time the phototactic 



