ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 287 



by the course of other internal processes ; these are, perhaps, the most 

 important factors determining physiological states. 



Of a somewhat diiferent character are the changes in physiological 

 state exemphfied in the behavior of Stentor and the flatworm. In Sten- 

 tor, as we have seen in Chapter X, we can distinguish at least five differ- 

 ent physiological states in which the same individual reacts differently 

 to the same conditions. Under stimulation by numerous grains of car- 

 mine in the water, the Stentor in condition No. i does not react at all. 

 In condition No. 2 it reacts by turning into a new position. In condition 

 No. 3 its reaction is a reversal of the ciliary current. In No. 4 it responds 

 by contracting at brief intervals. In No. 5 the contractions are stronger 

 and the organism remains longer in the contracted condition, finally 

 breaking its attachment to its tube and swimming away. Throughout 

 this entire series of reactions the external conditions remain the same, 

 so that we can attribute the different reactions only to different condi- 

 tions of the organism. 



In the flatworm we have seen in Chapter XII that six different physio- 

 logical conditions may be distinguished, in each of which the flatworm 

 is a different animal, so far as its reactions to stimuli are concerned. 

 We need not repeat the details regarding these conditions here. Illus- 

 trations of the fact that the reaction of the organism depends on its 

 physiological state might be drawn from the behavior of many other 

 animals. 



(5) The Physiological State may he changed by Progressive Internal 

 Processes, particularly those of metabolism. The well-fed sea anemone 

 or Hydra is a very different animal, so far as its behavior is concerned, 

 from the specimen that has fasted. Under uniform conditions, the sea 

 anemone that is well fed remains quiet; while the individual that has 

 exhausted the material for metabolism toils painfully away on a tour of 

 exploration. The well-fed individual reacts negatively or not at all 

 to that to which the hungry individual reacts positively. The Para- 

 mecium bursaria that has exhausted its supply of oxygen behaves in one 

 way with regard to fight, the individual in which respiration is progress- 

 ing normally in another way. Innumerable examples illustrating this 

 principle can be found in the behavior of lower and higher organisms. 

 It is hardly too much to say that the progress of the metabofic and other 

 physiological processes is the chief factor in determining the behavior' 

 of lower organisms. 



(6) The Physiological State may be changed by the Action of External 

 Agents. — This follows directly from the behavior of Stentor and the 

 flatworm, to which we have referred in the preceding paragraph. The 

 Stentor in condition No. i, as we have seen, does not respond to the 



