MOVKMKNTS, ETC., OF FRKSH-WATER PLANAHIANS. 705 



behaviour was composed of invai-iable reflexes is found in the 

 behaviour following repeated strong stimuli applied to the 

 anterior end (vide pp. 580, 581). In this case the organism 

 shows an evident modifiability in reaction, for after giving 

 for some time the ordinary negative reaction, and not thereby 

 getting away fi'om the stimulus, it finally turns directly 

 towards the source of the stimulus. Again, in the rig'htinar 

 reactions of pieces of the body we see entirely new forms of 

 reaction appearing (pp. 680 — 683). 



In order to give a concrete idea of the psychological 

 position of Planaria it may be well to present in parallel 

 columns the principal factors which make for simplicity in 

 the behaviour on the one hand, and for complexity on the 

 other hand. 



Factors wliicli tend to make 

 tlie Behaviour Simple. 



A. Essential reflex character at tlie 



basis of all the reactions. 



B. General lack of modifiability of 



reactions. 



C. Comparatively small number of 



qualitatively different reflexes 

 composing the general reac- 

 tions. 



Factors which tend to make 

 the Behaviour Complex. 



A'. Comparatively larjre number of 

 qualitatively difl'erent general 

 reactions. 



B'. Marked qualitatively difl'erent re- 

 actions to differing intensities of 

 stimulus. 



C. Definite relations of reactions to 

 location of stimulus. 



D'. Rather close dependence of reac- 

 tions on the physiological condi- 

 tion of the individual. This brings 

 about variation in the reactions. 



The behaviour of Planaria is evidently much more com- 

 plex than that of the Infusoria, as described by Jennings 

 (loc. cit.). In the case of the Infusoria, all the factors A', 15', 

 C, D', which make the behaviour of Planaria so complicated, 

 are nearly or quite absent ; and in respect to C these organ- 

 isms are at a much lower stage than Planaria. The 

 Infusoria have practically but one purely reflex reaction to 

 nearly all stimuli, and this reaction is not localised with 



