RHEOTAXIS IN ISOPODA 



263 



greater care was exercised to produce a uniform rate of current 

 in the successive trials than during the preceding experiments. 



Reaction to concussion 



In testing rheotaxis in a circular current there is no means 

 of measuring the stimulus acting at any given time ; consequently 

 one is not sure that the isopod is reacting to equivalent stimuli 

 in successive tests. This is more especially the case since the 

 circular current has a spiral rather than a direct course. It 



Fig. 1 Concussion apparatus. 



seemed possible that an adaptation of the concussion method 

 employed by Banta ('10, p. 453) might therefore furnish a more 

 exact method for determining the differing physiological states. 



Banta dropped a steel or lead ball to a pine board upon which 

 the isopod to be tested was placed in a wax bottomed Stender 

 dish. He does not speak of precautions to prevent the ball 

 from rebounding, and presumably none were taken. Of course 

 the vigor and number of the rebounds would vary partially as 

 the distance through which the ball was dropped; but when 

 this rebound is present the animals may and probably do react 

 to the succession of smaller shocks after being aroused by the 



