DEPENDENCE ON ASSOCIATION. 95 



ing us to the conclusion that the differences which 

 we find in the nervous action of animals, are differ- 

 ences of degree only and not of kind. The difference 

 lies in the complexity of organisation, and not in 

 the essential properties on which nervous activity is 

 based. We may infer, therefore, that these funda- 

 mental properties and laws of nervous activity are 

 the same for all animals which have a nervous 

 system. As the evolution of nervous systems from 

 undifferentiated protoplasm and undifferentiated tis- 

 sues, is a corollary of evolution — and we see it 

 occur in the development of each individual — there- 

 fore we may expect to find these properties existing 

 in some degree wherever we find living matter. We 

 have already had proof in a previous chapter of 

 the existence in plants of that fundamental nervous 

 property which displays so remarkably the effects of 

 repetition ; and we saw also how the effects of the 

 repetition remained for some time after the periodic 

 stimulus had been withdrawn. It may be objected 

 that I have assumed too much in stating that the 

 power of association and the effects of repetition are 

 so universal among organisms, but every co-ordination 

 of movements shows a power of associations ; and 

 every animal whose actions are intelligible to us, 

 seems to be able to learn, — and plants show rudi- 

 ments of the same capacity ; i.e. an activity neces- 



