476 A. M. Banta 



remained in the upper end lor about three-quarters of an hour, 

 after which fimp the animals that entered the light seldom re- 

 mained long. Caecidotea was not often swept back. It wandered 

 about in the light upper end for a time and entered the dark end 

 again apparently by accident. Often, too, it turned back into 

 the dark as soon as it came to the light area. 



Under the last conditions of experimentation Asellus seems 

 more rheotactic at first than Caecidotea, but this reaction persists 

 for a shorter time than in Caecidotea. Probably a better way of 

 describing this state in Asellus is that at first its rheotaxis is 

 stronger, as compared with its negative phototaxis, than Caeci- 

 dotea's, but that its rheotaxis soon gives place to negative photo- 

 taxis; while Caecidotea does not so soon cease to enter the light 

 as Asellus, it never enters and collects in the light in large num- 

 bers. Its negative phototaxis is from the first stronger than its 

 rheotaxis. 



In regions of caves the cave streams, as I know them, ordinarily 

 originate underground and flow out of the caves, although there 

 are many exceptions to this rule. In Mayfield's Cave, near 

 Bloomington, Indiana, which is the source of some of my material, 

 there is no inflow into the cave from above ground except through 

 sink holes in times oi heavy rains or thaws. The stream is mereh' 

 an outlet for underground drainage. 



The experiments in which the upper end oi the trough was 

 darkened while the lower remained fight, thus resembled in min- 

 iature the conditions met with in this cave. Judging from the 

 results of these experiments Asellus and Caecidotae ought both to 

 enter such a cave, but Asellus being less persistently rheotactic 

 would be less inclined to follow up the stream and remain within 

 the cave. Caecidotae, while less strongly rheotactic at the begin- 

 ning, is persistently so, and hence would tend to creep persistently 

 into the cave. The added fact that Asellus, after having been 

 in darkness for some hours, is positively phototactic would induce 

 the animals to leave a cave after once having become indifferent 

 to the current, provided that the)' were carried by accident to 

 within a glimmer of light. 



The experiments in which the lower end of the trough was 



