538 RAYMOND PEARL. 



coutents of the intestine can be seen to be in rapid motion. 

 Soen after the beginning of the contractions, Avhich are in 

 character different from any other of the movements of the 

 body which I have observed, and which cannot be adequately 

 described, the intestinal debris is shot out of the pharynx. 

 The force of the expulsion is so great that the f^ces spread 

 out in the water some considerable distance from the opening 

 of the pharjaix. I have observed the process only a few 

 times ; apparently it occurs only at infrequent intervals. 



V. Summary of Factors in Behaviour. 



From the above sketch the behaviour of the flat-worm can 

 be seen to be of considerable complexity. The movements 

 show many variations in character, rate, and direction. The 

 animal shows apparent preferences for certain situations 

 while avoiding others. It reacts to a variety of stimuli in 

 ways which, on the whole, further its preservation and well- 

 being perhaps as well as if guided by careful thought. It 

 chooses its food, taking certain things and passing by others. 

 It forms gatherings of a sort which apparently indicate that 

 the flat-worm prefers to be in the company of his fellows ; 

 in other words, it seems to have something of "social 

 instinct." On the whole, as the further analysis will show, 

 it fits itself to its environment by its activities in a way 

 which would not be discreditable to a being possessed of 

 considerable powers of reasoning. 



Our problem now is to analyse, as far as possible, this 

 complex behaviour into its component factors. Each activity 

 will be taken up in detail and subjected to thorough scrutiu}', 

 to determine its essential nature, and whether it may not be 

 resolved into simple components. With this analysis com- 

 pleted, it will be possible to assign the organism a definite 

 position in the objective psychological scale. With the 

 internal psychological factors — those of which there is no 

 objective criterion — we shall not attempt to deal. The 

 purpose of the paper is to furnish the data which may be 



