RHEOTAXIS IN ISOPODA 



307 



tube. In this way it is possible to keep water well aerated with- 

 out setting up strong currents. In fact by adjusting the rate of 

 flow of the bubbles and by keeping the tube from extending too 

 far into the water it was found that scarcely any current was 

 noticeable on the bottom of the container. 



Fig. 4 Modified Colton aerating apparatus 



This device has several advantages as a control in this kind of 

 experiments, for it enables one to keep the isopods in a well-aer- 

 ated, current-free medium. This avoids the possible mechanical 

 stimulation of the current and at the same time keeps the isopods 

 in the presence of their own waste products and thus in the same 

 conditions as prevail in the experiment, except as regards the oxy- 

 gen supply, and the possible increased oxidation of the waste. 



