86 DEVELOPMENT AND HEREDITY. 



cal ; they are both only the form of essentially the 

 same contents {gleickartigen luhalt)." Thus from 

 the occurrence of psychical changes we may infer 

 the occurrence of corresponding physical changes, 

 even though the latter by their subtlety may be 

 beyond detection by our present means of physical 

 observation. 



It is the peculiar property of living matter which 

 we recognise as an elemental nervousness, and which 

 so wonderfully transmits and transforms the forces 

 of the environment, that I hope to show is the basis 

 of that capacity for development which is inherent 

 in all organisms. In order, therefore, to understand 

 the nature of development, we must analyse the fun- 

 damental properties of nervous action. In doing 

 this, we need not hope to establish any obscure or 

 hitherto unnoticed nervous property as a cause of 

 phenomena so universal as development, but shall 

 turn our attention rather to properties that are 

 equally universal and apparent. 



If we turn to that development with which we are 

 most familiar, and which we can most easily analyse, 

 namely, our own later individual mental and bodily 

 development, we find that it is due to the effects 

 of repetition of actions and thoughts, and to asso- 

 ciation of the same. Says Mr. Sully : ^ " The com- 



1 " Mental Elaboration," Mind, No. Ix., October, 1890. 



