RHEOTAXIS IN ISOPODA 



283 



2. Two days later 65 per cent positive; 25 per cent negative; 

 10 per cent indefinite. 



3. Three days later 33 per cent positive; 23 per cent negative; 

 44 per cent indefinite. 



That is, in the early stages of the effects of these depressants 

 the isopod tends to show increased negative responses and later 

 when the depression is more complete the greater number of 

 responses are indefinite. 



Chart 7 Shoeing the positive rheotactic response and efficiency of isopod 

 nos. II and VI for twenty-four consecutive hours. The dots along the base 

 line represent hours. For details of charting, see chart 1, p. 275. 



Chart 8 A comparison of the positive reactions obtained from group tests 

 with the average daily positiveness of three or more individual isopods. The 

 group reactions are shown by the dotted line; the averaged individual responses 

 are shown as chart 1, p. 275. For discussion, see p. 292. 



RHEOTAXIS DURING THE MOLTING PERIOD 



Wege ('11) gives the following account of the molting process 

 in Asellus aquaticus: 



Sometime before molting, usually twelve to twenty-four hours, the 

 hypodermis begins to draw back from the body covering, whereby it 



