RHEOTAXIS IN ISOPODA 



289 



TABLE 5 

 Stream Aselli in straight current 



* Pan response taken after trough reversal; all others were taken before. The 

 first column gives the oxygen content of the water in cc. per liter. The second 

 gives the time in hours and minutes before there was a decided reversal in the 

 response to the current. The third column shows the percentage of positive 

 responses of the same animals to the circular pan current. The fourth column 

 shows the duration of the experiment in hours and minutes. The strength of the 

 current is given in cubic centimeters of flow per minute, the trough being placed 

 as nearly level as possible. In the three cases where no exact amount of oxygen 

 is shown, the amount present was well above air saturation at the given tempera- 

 ture. 



no appreciable change of position during this period when no 

 readings were taken. 



A study of table 5 will show that there is a relatively long lapse 

 of time before reversal. This length of time is correlated with the 

 high per cent of positive responses. This correlation is by no 

 means close, nor does it follow the fluctuations of the pan response 

 but the significance of the relation between the two is well shown 

 by comparing the results obtained here with those of isopods 

 kept in water having a low oxygen content. 



