RHEOTAXIS IN ISOPODA 



337 



Figure 10 gives the curve for the effects produced by stimulating 

 agents. Two distinct results were obtained with water saturated 

 with oxygen {B, D) . In one case (B) the isopods were already 

 giving an increased positive response due to the relatively high 

 oxygen content of the water. In both cases, however, the in- 

 creased positiveness was maintained until death resulted. The 

 isopods, however, become acclimated to both a higher tempera- 

 ture (A) and to a supply of caffein (C). When once acclimated to 



1 — \ — I — \ — I — \ — I — I — I — I — I — ' — I — I — r 



-1 — I — I — r 



I I I I 



t I I I I 1 I 1 I I — I — 1 — I — 1 — I — L 



Days 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 



Fig. 10 The effect of stimulating agents upon rheotaxis. A-, Increased tem- 

 perature, about ten degrees; B, D, saturated oxygen, 25 cc. per liter; C, caffein, 

 10-25 cc. saturated solution per liter. 



the latter, a further increase up to the point of toxicity caused 

 increases in the positive response. 



The experiments have also shown that the size of the isopods 

 and their rate of growth are correlated with the oxygen supply. 

 Also that when subjected to a gradient of different concentra- 

 tions of oxygen or carbon dioxide, Aselli will collect in the con- 

 centration nearest that to which they are accustomed. 



