228 University of California Publications in Zoology [Vol. 11 



that the animal swam against the current ; that under the heading 

 ( — ) negative shows the period during which the animal swam 

 with the current; and (=h) indifferent, the length of time that 

 the specimen hugged the bottom of the dish, going neither one 

 way nor the other. It was necessary at the beginning of each 

 experiment to make the current strong enough to release the hold 

 of the specimen on the bottom of the dish. 



Observation of the preceding table indicates the strongly 

 positive character of the rheotaxis of Dina. The animal re- 

 sponds by swimming for the greater part of the time vigorously 

 against the current. This positive rheotaxis is probably of con- 

 siderable significance to the animal. The usual habit of Dina 

 is quiet ponds, or near the edge of fresh-water lakes under stones. 

 A positive rheotaxis would tend to keep the animals in such 

 localities where they bred. Young individuals, one-eighth the 

 size of the adults, showed responses as decided as the older ones. 



No experiments were conducted to determine the rheotactic 

 responses of Glossiphonia stagnalis, since in this form there is 

 no swimming reaction and the principal effect of the current 

 would be to make the animal hug the bottom of the dish. 



