470 A. M. Banfa 



viduals which collected at the upper end of the trough was at- 

 tained in from five minutes to four and a half hours after the ex- 

 periment began, but on the average it occurred m about 1.4 hours. 

 The persistence of the response was extremely variable; in some 

 cases the animals remained at the upper end of the trough for 

 only about a quarter of an hour, while in one experiment (No. 16) 

 they stayed continuously for two days, after which they gradually 

 left the upper end of the trough. Commonly, however, the rheo- 

 tactic response did not persist more than two or three hours, and 

 in cases in which the experiment was run over night, the response 

 usually became decidedly reduced before the next morning. 



Table VIII shows the results ot the characteristic experiments 

 of this series. 



2. Ccpcidotea 



Caecidotea, when first subjected to a current of water, moved 

 about usually with little reference to its direction, though it some- 

 times reacted almost at once, crawling towards the upper end of 

 the trough. Caecidotea crawls more slowly than Asellus and 

 keeps more closely to the substratum, so that it is better able to 

 adhere to a fairly smooth surface than Asellus. It was not often 

 swept off its feet by a current of 435 cm. per minute, and it moved 

 about in the current with greater ease than Asellus. 



With Asellus the direction of the current could be readily 

 determined at almost any time during the beginning of an experi- 

 ment by examining the direction in which the animals within the 

 trough were headed. This was not so with Caecidotea, for often, 

 so far as their positions were concerned, one would not suspect 

 that there was a current. Caecidotea, while remaining on the 

 copper gauze partitions of the trough at times, did not do so as 

 persistently as Asellus did. 



After a time in most of the cases in which reactions did not 

 appear promptly, Caecidotea gradually collected toward the upper 

 end of the trough. The maximum rheo tactic response, i.e., the 

 collecting of the maximum number in the upper end of the trough, 

 with one exception occurred within | to 5 hours after the experi- 

 ment began and averaged about 2.1 hours. This rheotactic 



