AN EXPERIMENTAL ANALYSIS OF THE RELATION 



BETWEEN PHYSIOLOGICAL STATES AND 



RHEOTAXIS IN ISOPODA 



W. C. ALLEE 



From the Zoological Laboratory, University of Chicago 



TEN FIGURES 



CONTENTS 



I. Introduction 270 



1 . Material 272 



2. General reactions 273 



3. Methods 275 



II. Rheotactic response under natural conditions 280 



1. Stream Aselli 280 



a. Normal adults 280 



b. Breeding season 281 



c. Juvenile mores 285 



d. Response to straight current 287 



2. Pond Aselli 289 



a. Adults 289 



b. Juvenile pond isopods 292 



c. Response to straight current 293 



3. Summary of rheotactic response given under natural environmental 



conditions 294 



III. Rheotactic response under experimental conditions 296 



1. Stream Aselli 296 



a. With decreased oxygen 296 



(1) Normal adults 297 



(2) Breeding season 301 



(3) Juvenile stream Aselli 304 



(4) Response to straight current 308 



b. Carbon dioxide 309 



c. Chloretone 313 



d. Potassium cyanide 314 



e. Low temperature 316 



f . Starvation 317 



269 



