CONTENTS 



Page 



Historical background 375 



Major theories on orientation 375 



Sensory basis of orientation 376 



Relation of sensory abilities to environmental patterns 376 



Experimental approach 378 



Materials and methods 378 



Experimental method 379 



Procedure 380 



Controls ^ 381 



Water modification 382 



Temperature 382 



Gaseous content 382 



Nongaseous chemicals ^ 383 



Measurements 383 



Water samples 383 



Titrations 384 



Hvdrogen-ion concentration 384 



Alkahnity and HCO7 384 



Carbon dioxide t 384 



Oxygen 385 



Temperature 385 



Velocity 385 



Aberrat ions in experimental control 385 



Exijpriments 386 



Orientative influence of temperature 386 



Relation of temperature response to temperature level 387 



Orientative influence of CO2 387 



Relative orientative influence of CO2 and temperature 388 



Orientative influence of pH 388 



Experiments using nitrogen and oxygen 389 



Nitrogen " 389 



Oxygen 389 



Other factors influencing orientation 390 



The 3:1 ratio of the response 391 



Discussion 392 



Summary 394 



Literature cited 395 



