294 



W. C. ALLEE 



TABLE 8 

 Pond Aselli in straight current 



* Time before reversal and the length of experiment are given in hours and 

 minutes; the pan response is in terms of the per cent of positive reactions. The 

 current was kept at 1040 cc. per minute. 



t With brood pouches unable to stay on bottom. 



X Almost no positive response at all. 



direct way. But if there were a shock effect the result would be a 

 lengthened response, so that perhaps the two might offset each 

 other to some extent. Then, too, the experiments were in running 

 water with a large amount of oxygen, because at this time there 

 was no means of controlling the amount of oxygen present in 

 water flowing at the rate used here. 



The animals used in the first, second, and last trials were kept 

 in running tap water for the length of time they had been in the 

 laboratory. In the first two cases the animals were not exposed 

 long enough to cause any effect upon their reaction, so the oxygen 

 content of their original habitat is given. In the last trial the 

 high oxygen evidently had not made any change in the response 

 of the isopods, but this may have been due to the fact that these 

 were females with large brood pouches that made it impossible 

 for them to keep their footing in the strong current. 



3. SUMMARY OF RHEOTACTIC RESPONSE GIVEN UNDER NATURAL 

 ENVIRONMENTAL CONDITIONS 



In discussing the normal rheotactic responses of A. communis 

 it has been shown that the same species is found in both ponds 

 and streams, but that it is limited in the latter to those having 



