RHEOTAXIS IN ISOPODA 



293 



facts shown by the table support the experiments already dis- 

 cussed. The two responses marked 'M.d.' in the table show the 

 reactions of juvenile Mancasellus danielsii. These trials were 

 made in spring and summer and the two instances of lower tem- 

 perature, are due to the animals being kept in an ice box. How- 

 ever, they were left in each case long enough to become thoroughly 

 acclimated and so showed no effect of the continued low tempera- 

 ture. ' 



c. Response to straight current 



Only five trials have been made with pond isopods from water 

 with a low oxygen content but as was the case in the stream ani- 

 mals these support the pan reactions, in that they show a short 

 period of positive response to the straight current correlated 

 with the low response in the pan reactions. A summary of the 

 reactions is given in table 8. 



The conditions of the trials were exactly like those already 

 described for this method. Owing to imperfect apparatus it 

 was not possible to keep the temperature exactly the same in 

 these trials and the variation in the second and fourth tests is 

 enough to cause some difference in the response. In both cases 

 this would tend to shorten the positive reaction if it acted in a 



* Mancasellus danielsii. 



