RHEOTAXIS IN ISOPODA 



319 



TABLE 21 



The effect of high oxygen upon rheotaxis in adult pond Aselli 



* The amount of oxygen present was at least 5.12 cc. per liter. 



With the exception of the last two items, this table deals with 

 one stock kept in a large aquarium in running water. The tests 

 were made by selecting individuals at random and so give a fair 

 representation of the reaction of the group. The increase in 

 positive responses is not great but it is marked enough and con- 

 stant enough to show that increasing the amount of oxygen pres- 

 ent will affect the rheotactic reaction. One very significant fact' 

 is that there is no evidence of acclimatization in this or any sub- 

 sequent test. The last two items show the same response with 

 isopods kept in still water which gained its increased oxygen 

 supply from the photosynthesis of Amblistigium moss. 



If increasing the oxygen present in the water 5 cc. per liter 

 caused an increase in the positive response, then increasing the 

 concentration still more should cause a yet greater increase of 

 the positive reaction. In order to test this, oxygen was bubbled 

 through the aerating device previously described. The oxygen 

 gave the following analysis; oxygen, 99 per cent, carbon dioxide 

 trace, nitrogen 0.95 per cent. The results are listed in table 22. 



The increase in the oxygen caused a decided increase in the 

 positive reactions as well as in the general activity. Where 

 isopods in the control crawled slowly these ran rapidly, often 



