BRAIN PHYSIOLOGY OF WORMS 367 



only a quantitative difference exists so far as spontaneity is 

 concerned ; when we designate as spontaneous those changes 

 in an animal which are the result of internal, or more cor- 

 rectly, which occur without demonstrable external stimuli. 

 As a matter of fact, many changes brought about through 

 external stimuli will seem spontaneous to us because the 

 external stimulus escapes our observation. We have to dis- 

 tinguish between conscious spontaneous changes (the true 

 will-action in which the idea of the coming change precedes 

 the latter) and simple spontaneous changes in which internal 

 causes determine the latter without processes of conscious- 

 ness being present. In the case of worms, of course, we can 

 speak only of the latter forms of spontaneity. In Thysano- 

 zoon this spontaneity seems to be exclusively a function of 

 the brain. In Planaria torva, on the other hand, this is not 

 so distinctly the case. When compared with the number of 

 reactions to external stimuli the number of the spontaneous 

 movements of worms is small. Only where associative 

 memory is present do the spontaneous changes step into the 

 foreground numerically. 



5. Whether the sensations of pleasure and pain are pos- 

 sible without consciousness cannot be decided absolutely. 

 If it is permissible to consider the reactions of a frog when 

 its skin is touched with acid, or the bending of a worm 

 when one steps on it, as an expression of a sensation of pain, 1 

 our experiments show that all pieces of a worm are capable 

 of the sensation of pain. It is worthy of notice, how- 

 ever, that the reactions pointing to sensations of pain are 

 weaker in Planarians than in Annelids, or may be lacking 

 altogether. 



6. One might be led to believe that the reflex motions 

 in higher animals depend to a higher degree upon the 



i W. W. NORMAN has since shown that this is not permissible. The problem is 

 more fully discussed in my book on the Comparative Physiology of the Brain. [1903] 



