Brain PuysioLtocy or 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,’ 
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 
1W. 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] 
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