290 • J. M. Banta 



the number in the illuminated end rapidly decreased. However, 

 the photokinetic effect usually did not cease at once when the 

 animals entered the dark region, hence many of them on reaching 

 the end of the tank, turned back and often wandered in to the illumi- 

 nated region again. Since in this experiment the animals had been 

 in the tank but an hour, the thigmotactic or other influence due 

 to the transference of the animals to the tank was still effective. 

 These influences caused the animals to move about so vigorously 

 that they kept entering the illuminated region rather freely for 

 over an hour. However, since the activity w^as less in the dark 

 end, that factor alone served to keep the number in the dark region 

 in excess of that in the illuminated region. When the thigmotac- 

 tic and photokinetic influence became less strong the number in 

 the illuminated region became quite small and remained so. The 

 observations of Table IX will serve to illustrate the nature of 

 the experiments of this series, which are summarized in Table X. 

 In all these the Asellus were confined in the tank, one half of 

 which was exposed to vertical illumination of 6983 CM., while 

 the remaining half was very faintly illuminated. 



This series of experiments shows Asellus to be extremely respon- 

 sive to vertical illumination of 6983 CM. intensity. In the end 

 virtually all of the animals, remained in the dark region entirely 

 out of range of the strong light. 



Byway of general summary of this series of experiments 

 with Asellus the following conclusions are draw^n: 



1 The photokinetic effect in the illuminated end of the tank 

 is very marked. 



2 Photokinesis causes some of the animals to start up sud- 

 denly soon after they are exposed to the light, and a generally 

 increased activity soon results. 



3 When headed toward the illuminated space the sudden illum- 

 ination of the animal upon crossing the plane between the dark 

 and the illuminated region sometimes causes the animal to stop 

 abruptly. 



4 When the animal is made to stop by this sudden illumina- 

 tion, it often reacts in a characteristic way. 



