406 



W. C. ALLEE 



long survival-period while the very weak ones die soon after being 

 placed in the cyanide. In this regard the cyanide method would 

 fail to measure the metabolic rate. This may be due to there 

 being just enough oxidation carried on to keep the isopod alive, so 

 that when the cyanide decreases this ever so little death speedily 

 results. 



In another paper (Allee '13) it was pointed out that the effi- 

 ciency of reaction in the water current varied more or less closely 

 with the percentage of positive responses. That this is also an 

 expression of the metabolic condition of the isopod is shown by 

 the data presented in table 3. 



TABLE 3 



Showing the relation between the survival-time in potassium cyanide and the 

 efficiency of the response to the current of water. Temperature 17 to 21° C. 



The results exhibited in table 3 are too few to be more than 

 indicative; however, since they agree with all the other observa- 

 tions I think they approximate the truth of the situation. This is 

 that while high efficiency in the current usually accompanies a 

 larger percentage of positive responses and a higher rate of metab- 

 olism than low efficiency, yet considered alone the differences 

 are neither so marked nor so sure as when the sign of the rheo- 

 tactic reaction is made the index of the metabolic condition. 



One pertinent comparison remains in the relation between 

 survival-time and rheotaxis. What are the rheotaetic reactions 



