PHYSIOLOGICAL STATES AS DETERMINING 

 FACTORS IN THE BEHAVIOR OF LOWER 

 ORGANISMS. 



NATURE AND EVIDENCES OF PHYSIOLOGICAL STATES. 



In studying the behavior of the lower organisms the units of obser- 

 vation, the factors to which especial attention has been paid have been 

 usually the tropisms and reflexes. These factors may be considered 

 as determined mainly (i) by the action of external agents on the 

 organism ; (2) by the structure of the organism. 



An examination of the results of the study of reactions in the lower 

 animals up to the present time shows, I believe, that we must recog- 

 nize another set of factors in their behavior, of equal importance with 

 either of those already named. This set of factors may be characterized 

 by the general term physiological states, 



By physiological states we mean the varying internal physiological 

 conditions of the organism, as distinguished from permanent anatomical 

 conditions. Such different internal physiological conditions are not 

 directly perceptible to the observer, but can be inferred from their 

 results in the behavior of the animal. These results are of so marked 

 a character that the inference to different physiological conditions is 

 beyond question. 



In the study of tropisms and reflexes a considerable number of 

 instances have been brought to light of changes in the reaction methods, 

 such as can be attributed only to changed physiological conditions. 

 Some of these cases will later be considered in detail in this paper. 

 Comparatively few investigations on the behavior of lower organisms 

 have been published in which attention has been consciously directed 

 to these physiological states, and in most of these the matter has been 

 taken up rather incidentally. We may mention as instances of papers 

 dealing more or less with this aspect of the matter that of Hodge and 

 Aikins (1895) on Vorticella, those of Von Uexkiill (1899, 1900, 1900, a, 

 1903) on the sea urchin and on Sipunculus, my own on the behavior 

 of fixed Infusoria (Jennings, 1902), and that of Pearl (1903) on the 

 flatworm. In the study of higher organisms attention has of necessity 

 been largely directed to the phenomena determined by varying physio- 

 logical states, as these play a striking part in the behavior. 



In the present paper an attempt will be made to collect and analyze 

 a number of the known cases showing the influence of physiological 

 states on the behavior of the lower animals, pointing out some of their 

 bearings on the theories of behavior. 



