RHEOTAXIS, RESISTANCE TO POTASSIUM CYANIDE 



407 



which accompany relatively long and relatively short resistance 

 to potassium cyanide? A synopsis of these results is presented 

 in table 4. 



Upon making this comparison one is struck, first by the relative 

 closeness of the rheotactic responses given under the two condi- 

 tions and second by the fact that the longer survival-times have 

 always the lower percentage of positive responses. One of the 

 factors causing the relatively low percentage of positive rheo- 



TABLE 4 



Showing the relation between long and short survival-time and rheotaxis. 



ture 17 to 21° C. 



Tem-pera- 



tactic reactions with the shorter survival-periods is that isopods 

 sometimes give a high degree of negativeness with a relatively 

 short survival-time (cf. Allee '13), although on the average such 

 isopods live longer in the cyanide than do highly positive ones 

 (see also p. 405). 



The indirect method 



Only isopods from Stock II were tested by this method. These 

 were placed in 0.00001 molecular postassium cyanide solution in 

 two-liter flasks immediately after having been tested for rheo- 

 taxis. Three easily distinguished individuals were placed in each 

 flask. In order to secure more even temperature the flasks were 

 placed in running water. The temperature averaged 18° C, but 



