308 



W. C. ALLEE 



In the case of these experiments, the isopods were put into this 

 aerating device in the water in which they had been reared and 

 this water was not changed. From table 13 it will be seen that 

 the isopods in the aerated water, not only responded to currents 

 with a much stronger degree of positiveness, but that their rate 

 of growth was more rapid. In this case the supply of oxygen 

 is the only factor known to have varied. 



(4) Response to straight current. The effect of keeping stream 

 isopods in low oxygen is more marked if tested in a straight cur- 

 rent, than when only the pan responses are compared. The lack 

 of adequate apparatus in the early part of the work is more clearly 

 shown in these experiments than when the pond reactions were 

 being discussed. All of the trials except the second and fifth 

 shown in table 14, were made before the later apparatus was 

 built. In these cases it was impossible to control the oxygen 

 supply or the temperature during the trough tests. It was there- 

 fore necessary to test the isopods from low oxygen and room tem- 

 perature, in cold tap water having a high oxygen content. Under 

 these conditions it is remarkable that the results in the rest of 

 the table compare as well as they do with the results obtained 

 under properly controlled conditions. , 



TABLE 14 

 Stream Aselli from low oxygen in straight current 



cc. per liter 



(1) 3.96 



(2) 

 (3) 

 (4) 

 (5) 

 (6) 

 (7) 

 (8) 

 (9) 

 (10) 



3.57 

 3.80 

 4.00 

 0.57 



3.96 



2.28 

 2.28 



LENGTH OF 

 EXPERIMENT 



3:47 



26:57 



4:02 



2:14 



3:00 



4:19 



2:28 



2:43 



18:35 



18:35 



CURRENT 

 STRENGTH 



1680 



1050 

 1000 

 1020 

 1050 

 1000 

 1680 

 1000 

 1050 

 1050 



TEMPERATURE 



Trough Aquarium 



17 

 11 

 16 

 15 

 13 

 18 

 5 

 5 

 10 

 10 



18 

 11 

 IS 

 17 

 15 

 13 

 18 

 19 

 17 

 17 



* As before, the time given is in hours and minutes. The pan response is 

 stated in terms of the per cent of positiveness. The strength of the current is 

 given in cubic centimeters of flow per minute. In the sixth and eighth trials the 

 amount of oxygen was well below the point of air saturation. 



