RHEOTACTIC REACTION OF STREAM ISOPODS. 



59 



TABLE I. 



Showing the effect of orientation upon the strength of current in which isopods 

 can maintain their position. These tests were made under entirely identical 

 conditions throughout. In testing each animal, one to three trials were made with 

 the isopod facing in one direction then the orientation was reversed and an equal 

 number of trials were made. This was done to equalize possible fatigue effects. 

 For further details of the method used see p. 57. 



Oriented Positively. 



General average of 64 trials, 2,534 ( 7 2 ) 



Oriented Negatively. 



General average of 64 trials, 1385 ( 82). 



in quite strong currents when headed at right angles to them. In 

 doing this an isopod used the feet of one side as anchors and 

 swung below them. This method of maintenance gave erratic 

 results with the apparatus used. It also brought the isopod 



1 Copulating pair. 



