INTRODUCTION. 21 



neons. I am fully convinced that species arc not immutable , 

 but that those belonging to what are called the same genera 

 are hncal descendants of some other and generally extinct spe- 

 cies, in the same manner as the acknowledged varieties of any 

 one sjiecies arc the descendants of that species. Further- 

 more, I am convinced that Natural Selection has been the 

 most important but not the exclusive means of modification. 



