278 



W. C. ALLEE 



The results of another check on the constancy of the rheotactic 

 response to a circular current are given in figure 1, which shows 

 graphs of twenty-five successive responses of one male Asellus. 

 The animal used was a stream isopod 11 mm. long, that had been 



21 22 23 24 25 



Fig. 1 Twenty-five successive I'heotactic reactions of one stream Asellus 



kept in water with the oxygen at air saturation. In this case 

 the trials were made in a glass dish 10 cm. in diameter. The 

 current used was strong enough to sweep the isopod to the center 

 each time and the presence of the spiral current is plainly shown 

 by the path taken in reaching the circumference of the dish.. 



