RHEOTAXIS IN ISOPODA 



297 



TABLE 9 



The effect of the deaerating apparatus upon the salt content of the ivater. A = 

 Boiled in apparatus. B = Hot tap water. C = Cold tap ivater. Results are 

 given in parts per 100,000 



In the experiments the hot water (B) from the University heating system was 

 treated in the apparatus and the table shows that this treatment made it more like 

 the ordinary tap water, as far as the contained salts are concerned. 



used as a cover and was sealed down with vaseline, care being 

 taken to avoid enclosing any air bubbles. In experiments that 

 were run some time a few leaves were placed in the jar for food. 

 The water was changed often enough to provide an even supply 

 of oxygen. 



{1) Normal adults. Table 10 shows the results of a number of 

 trials in which, with the exception of no. 9, the oxygen content of 

 the water was low at the time of the trial and had been low for at 

 least ten days. The purpose of the table is simply to show the 

 typical response of stream isopods that have been kept in low oxy- 

 gen. It will be noted at once that the reaction is decidedly differ- 

 ent from that of the normal stream Aselli, in that the positive 

 percentage is lowered and the amount of indifference to the 

 current is correspondingly increased. It is significant that the 

 lowest positive responses are made by the animals in the lowest 

 oxygen, and that above 3 cc. the response becomes more variable 

 although in the main it increases as the oxygen supply increases. 

 The reactions that are grouped under no. 9 in table 10, were given 

 by isopods that had been in running water up until twelve days 

 before this trial was made. At that time they were giving a 70 

 per cent positive response in an oxygen content of 5.92 cc. per 

 liter. The water was turned off and three different trials made, 

 with the results recorded. From the variation, this seems to be 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 13, NO. 2 



