I 



TWO OBJECTIONS CONSIDERED 



in our ninth chapter were seen to overthrow the 

 dogma of fixity of species may now be added 

 the argument that at least one group of clearly 

 defined agencies is at work, with which, in the 

 long run, the fixity of species must become in- 

 compatible. The explanation of the details of 

 specific differentiation may well form the subject 

 of cautious investigation for many generations of 

 observers and thinkers. But enough has already 

 been explained to draw forth the undeniable 

 Fact of Derivation from the region of mystery 

 in which it was formerly half hidden, and thus 

 to place the Theory of Derivation upon a thor- 

 oughly scientific basis. In expounding the way 

 in which this has been done, we have obtained 

 several useful conceptions, which will not fail to 

 do us good service in future chapters. 



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