290 W. C. ALLEE 



efficiency is decreased while the number of negative reactions 

 is often increased (p. 285). 



II. Relation between vigor of response to concussion and 

 rheotaxis : 



1. In the daily variations there is no apparent relationship 

 between the vigor of the response to shock and either the sign 

 or the efficiency of the rheotactic reaction (p. 268). 



2. The greater variations show no more relation than do the 

 smaller ones (charts 1-6, pp. 275-282). 



3. The average vigor of shock reaction which accompanies low 

 and high efficiency; low and high percentage of positive reac- 

 tions; and low and high percentage of indefinite reactions are 

 practically identical. The vigor of concussion response that 

 accompanies a high percentage of negative reactions is slightly 

 higher than the others (pp. 269-273). 



4. Under the influence of potassium cyanide and low oxygen 

 the vigor of the shock reaction often increases at first as the 

 percentage of positive responses and rate of efficiency decrease, 

 but later decreases and becomes zero before death occurs (p. 279). 



5. There is some evidence of an increased sensitiveness to shock 

 stimuli during the molting period (p. 289). 



III. More variations occur in the percentage of positive 

 responses than can be accounted for by variations of known 

 external or internal factors (p. 274). 



IV. Potassium cyanide and low oxygen act at different rates 

 in different isopods but in all there is finally a depression reac- 

 tion from which the isopods may recover if placed in normal 

 conditions (p. 279). 



V. The length of the molting cycle varies greatly in different 

 individuals and in successive cycles of the same individual and 

 causes certain variations in the rheotactic reaction (p. 285). 



DISCUSSION 



With these results in mind it becomes pertinent to inquire into 

 the relation between the reactions of individual stream and pond 

 isopods. Nothing can be said of the limits of individual varia- 

 tion among pond mores because no work as yet has been done 



