ii DARWIN'S HYPOTHESIS 149 



account for all the phenomena which come within 

 the range of its operation. If it is inconsistent 

 with any one phenomenon, it must be rejected ; if 

 it fails to explain any one phenomenon, it is so 

 far weak, so far to be suspected ; though it may 

 have a perfect right to claim provisional accept- 

 ance. 



Now, Mr. Darwin's hypothesis is not, so far as 

 I am aware, inconsistent with any known biological 

 fact; on the contrary, if admitted, the facts of 

 Development, of Comparative Anatomy, of Geo- 

 graphical Distribution, and of Palaeontology, become 

 connected together, and exhibit a meaning such as 

 they never possessed before ; and I, for one, am 

 fully convinced, that if not precisely true, that 

 hypothesis is as near an approximation to the 

 truth as, for example, the Copernican hypothesis 

 was to the true theory of the planetary motions. 



But, for all this, our acceptance of the Dar- 

 winian hypothesis must be provisional so long as 

 one link in the chain of evidence is wanting ; and 

 so long as all the animals and plants certainly 

 produced by selective breeding from a common 

 stock are fertile, and their progeny are fertile with 

 one another, that link will be wanting. For, so 

 long, selective breeding will not be proved to be 

 competent to do all that is required of it to pro- 

 duce natural species. 



I have put this conclusion as strongly as 

 possible before the reader, because the last posi- 



