292 



W. C. ALLEE 



TABLE 6 

 Rheotactic response of adult pond Aselli 



different sources of evidence tend to show that this amount of 

 carbon dioxide is not sufficient to account for the difference in 

 behavior. This problem will be considered later under the 

 experiments upon the effect of carbon dioxide. 



b. Juvenile pond isopods 



The young isopods were tested for their response to current 

 when they were about forty-five days old. At that time they 

 were 3 mm. in length. As was the case in the stream animals 

 they gave a low positive response, behaving in almost every 

 respect like stream isopods of the same size. But as will be seen 

 in table 7 the later response did not show the increase in positive- 

 ness that was found in the developing stream forms. The other 



