252 DEVELOPMENT AND HEREDITY. 



of development and heredity, it may be well to 

 point out its relation to other scientific theories. In 

 the first place, it is an effort to extend the appHca- 

 tion of the law of the conservation of energy to the 

 phenomena of living matter, and to resolve the pre- 

 mises given us by the science of physics to their 

 logical conclusion in the realm of Biology. On the 

 other hand, it is the extension to all living matter 

 of certain fundamental properties of life which psy- 

 chology has either proved or tacitly assumed to 

 exist in the higher animals, the possible existence 

 of which in the lower animals has aroused so little 

 interest that it has perhaps never been discussed. 

 I mean here those properties expressed by the law 

 of repetition and association. I think none who 

 will review the facts of animal existence will deny 

 the universality of those properties. 



By pursuing the method of applying these wide 

 generalisations to the phenomena of life, the lat- 

 ter appear in a new light before us, and a har- 

 mony heretofore hidden becomes apparent. Growth, 

 development, and heredity are all due to one com- 

 mon principle. The complex relation of organism 

 to environment may be better understood ; the 

 broad facts of embryology and morphology are 

 explained, and fall harmoniously into their place in 

 the system. Much, of course, is lacking in detail. 



