USE AND DISUSE, REVERSION, AND HYBRIDISM. 77 



ever, they are so * yet the whole subject of 

 hybridism is as yet so little understood that we 

 cannot affirm positively whether or not the 

 difference between species and races is one of 

 kind, or only one of degree ; and although 

 the latter view is still very far from being esta- 

 blished, it would be rash to affirm that the 

 former is the only admissible theory. 



