Reactions of I so pods to Light 



TABLE VII Continued. 



271 



jected to stimulation by directive light the photokinetic effects 

 v^ere very marked. The apparent phototactic effects occurred 

 only when these photokinetic effects had become less evident. 



Further, the photokinetic effect with Caecidotea is stronger in 

 comparison with the apparent phototactic effect than it is in the 

 case of Asellus, where the phototactic effect is fairly well marked. 



Caecidotea was subjected to various intensities of horizontal 

 illumination from 5 CM. (8 c.p. incandescent at 1.3 m. from 

 middle of tank) to 2855 CM. (772 c.p. 6-glower Nernst lamp at 

 0.52 m. from middle of tank). No clearly directive responses were 

 obtained to intensities lower than 80 CM. (19 c.p. at 0.49 m. 

 from middle of tank). 



Caecidotea usually shows a negative response to intensities of 

 80 CM. or greater. Table VII shows the results of an experiment 

 with twenty-six Caecidotea, which had previously been exposed to 

 dayhght, when they were subjected to horizontal illumination of 

 an intensity of 2855 CM. The records were begun five minutes 

 after the animals were transferred to the tank. 



This is a fairly typical experiment. The animals having been 

 in the tank only five minutes when the records were begun, the 

 thigmotactic and other influences due to transference to the tank 

 were shown to good advantage. More than an hour elapsed after 

 the beginning of the experiment before any marked indication of 

 a directive response to light appeared, and that response was prob- 



