STERILITY OF HYBRIDS. 415 



that the sterility of hybrids was never slowly acquired, 

 but that it is "a special endowment;" that varieties 

 are hot " incipient species," nor ever can become dis- 

 tinct species ; and that each species is physiologically 

 fixed. 



Now, let us see, what the facts should be, to meet 

 the requirements of his hypothesis (what, indeed, by 

 the above argument of his, he intimates that they 

 should be); and then observe what the facts really 

 are, by his own showing. It will then be seen, that 

 the sterility of hybrids is not the only physiological 

 argument, in favor of the fixity of the species; but 

 that the fertility and sterility of individuals of the 

 same species, add arguments of even superior weight, 

 in demonstration of the same fact, of the immutability 

 of the species. 



Here is what it was absolutely requisite, that Dar- 

 win should have shown, to obviate the objection of 

 the sterility of species, and of their hybrids : — 



Seeing, that hybrids, — the result of a cross between 

 different species, — are invariably sterile, it is clear that 

 if the conception, that the varieties of a species were 

 " incipient species," or species in the process of forma- 

 tion, were a true one, we should expect, that the more 

 marked, distinct, and widely divergent such varieties 

 became, they would grow sterile, in proportion, when 

 crossed with each other; as sterility is the character- 

 istic of distinct species : 



If the differences, between varieties, do really be- 

 come augmented into the greater differences between 

 species, all fertility, among the mongrels of such varie- 



