270 W. C. ALLEE 



2. Pond Aselli 317 



a. With increased oxygen .317 



(1) Adults 317 



(2) Juvenile mores 321 



(3) Response to straight current 321 



b. Caffein..... 323 



c. Increase of temperature 326 



3. Effect of oxygen "on size 326 



4. Reactions to gradients of gases 328 



5. Summary of experimental results 332 



I V. Discussion 338 



Bibliography 342 



I. INTRODUCTION 



This paper is the result of an investigation into the role played 

 by the 'physiological state.'- of the organism in determining its 

 reactions. Jennings ('06, pp. 286-292) summed up the work 

 along this line, by Moebius ('73), Romanes ('85), Preyer ('86), 

 Uexklill ('97, '99, '00,) Yerkes ('02), Smith ('02), Pearl ('03), 

 Mast ('03), Bohn ('03, '03 a, '05), Gamble and Keeble ('03), 

 Yerkes and Huggins ('03), Jennings ('04 b, '04d), Spaulding ('04), 

 Holmes ('05) and Harper ('05). From this work he drew the 

 following conclusions: (1) Changes in activity depend on changes 

 in physiological states. (2) Reactions to external conditions 

 depend on physiological states. (3) The physiological state 

 may be changed by (a) progressive internal processes, (b) by the 

 action of external agents, (c) by the activity of the organism. (4) 

 External agents cause reactions by changing the physiological 

 state of the organism. (5) The behavior of the organism at 

 any moment depends on its physiological state at that moment. 

 (6) Physiological states change either according to the laws 

 affecting metabolism or according to those controlling stimula- 

 tion. 



These statements, however, were supported by little direct 

 experimental evidence and Jennings recognized this, for he says 

 ('06, p. 251): 



The diverse physiological states of lower organisms have been little 

 studied This is partly because it is rarely possible to observe them 

 directly; it is onl}' through their effects upon action that they become 

 evident. Thus the real data of observations are the actions; if we (?on- 



