268 W. C. ALLEE 



The minor daily variations of the number of positive reactions 

 and the efficiency of the rheotactic response run more closely 

 parallel with each other than either does with the variations in 

 the reactions to shock. The shock variation and the variation 

 in positiveness oppose each other almost as often as they agree. 

 The reaction to shock and efficiency are a trifle more uniform 

 in their variation but not enough so to warrant any claim of 

 agreement. It is probably significant that in all cases the agree- 

 ment is more pronounced when the vigor of reactions decreases 

 than under other conditions. 



There is another way of determining the relation between 

 these different factors : one may compare the concussion responses 

 and efficiency accompanying a state of high positiveness with 

 those found with a low percentage of positive responses. The 

 results of such a comparison are shown in table 4. 



In this table the efficiency and shock reactions which were 

 given by animals showing a positive response of 80 per cent 

 or over are compared with those accompanying 40 per cent or 

 less of positive rheotactic reactions. The table shows that in 

 every case the high percentage of positiveness is accompanied 

 by a high degree of efficiency in the current. In the main 

 a low efficiency accompanied a low positive reaction; but 

 this was not always true, notably in isopods nos. VII, XII and 

 XIX. These isopods gave more negative responses to the cur- 

 rent than positive and showed as high efficiency when negative 

 as when they were positive. However, the average shows almost 

 as marked a difference in the efficiency as in the positiveness. 



Again, there is no relationship between the reaction to shock 

 .and the positiveness of the isopods. It is evident from the table 

 that while low vigor of reaction to shock may accompany a sim- 

 ilar status of the rheotactic factors such is not necessarily true. 

 The case of isopod no. I is significant. This animal gave much 

 more vigorous shock reactions when giving a low positi^^e and 

 low vigor response than under the reverse conditions (see also 

 p. 272). The average of all the responses is practically the same 

 regardless of whether given with high or low rheotactic positive- 

 ness. 



