280 



W. C- ALLEE 



II. RHEOTACTIC RESPONSE UNDER NATURAL CONDITIONS 



1. STREAM ASELLI 



a. Noriyial adults 



Table 1 and figure 1 show responses of stream isopods at their 

 highest rate of positiveness. Usually under the conditions used 

 the per cent of positive response was somewhat lower. A list 

 of the results of these tests is given in table 2. It will be seen that 

 the results of different trials vary somewhat, the greatest varia- 



TABLE 2 



Nonnal rheotactic response of adult stream Aselli 



