RHEOTAXIS OF ISOPODS 211 



'13.) In order to analyze this behavior it is necessary to follow 

 the variations in the daily metabolism which obviously cannot 

 be done by the cyanide method because that depends on the 

 death point of the animals. Daily determination of the carbon 

 dioxide output of the isopods in connection with a daily test 

 of the rheotactic reaction proved feasible. The carbon dioxide 

 determinations were made by Tashiro in the manner already 

 given (page 203). The rheotactic reactions were tested by Allee 

 and neither knew the results of the other until the end of the 

 tests. The results obtained are listed in tables 3 and 4. 



From the results exhibited in table 4 it is seen that with both 

 isopods No. 102 and No. 12 six of the seven changes of carbon 

 dioxide production and the rheotactic response run in a parallel 

 direction. This means that with these two isopods 86% of the 

 variations in carbon dioxide output and rheotactic reaction were 

 similar. The amount of variation is not always proportionate 

 but it should be remembered that the isopods were able to move 

 to a limited degree in the respiration chamber and that this 

 caused an increase in the carbon dioxide production that was 

 not controlled. Also there is a possible error of about 5% in 

 the method of ascertaining the sign of the rheotactic reaction. 

 (Allee, '12.) In view of these considerations the experimental 

 results are about all that could be expected and are certainly 

 more exact than any previous observation on the correlation 

 of the behavior of animals upon their metabolic rate or phys- 

 iological state. 



Incidentally the table shows an agreement in the direction 

 of variation of carbon dioxide production and the oxygen ten- 

 sion in the water in which the isopods were kept in 66% of the 

 cases. The variations in the rheotactic response and oxygen 

 tension agree in 73% of the cases. This seems to be good 

 evidence that all three of these factors are more or less closely 

 related. 



The evidence here presented also makes it apparent that 

 each individual isopod has in all probability a different rate of 

 metabolic activity from that of any other isopod, (cf. Allee, '14) 

 and farther that it is not a fixed standard of metabolism that 

 accompanies a high degree of positiveness in the rheotactic 

 response but rather a relative rate. Thus on the average iso- 

 pod No. 102 (length 8 mm.) gave off over twice the amount 



