XI PHENOMENA OF ORGANIC NATURE 465 



duced from a common stock two breeds which are 

 not more or less fertile with one another. 



I do not know that there is a single fact which 

 would justify any one in saying that any degree of 

 sterility has been observed between breeds abso- 

 lutely known to have been produced by selective 

 breeding from a common stock. On the other 

 hand, I do not know that there is a single fact 

 which can justify any one in asserting that such 

 sterility cannot be produced by proper experiment- 

 ation. For my own part, I see every reason to 

 believe that it may, and will be so produced. For, 

 as Mr. Darwin has very properly urged, when we 

 consider the phenomena of sterility, we find they 

 are most capricious ; we do not know what it is 

 that the sterility depends on. There are some 

 animals which will not breed in captivity ; whether 

 it arises from the simple fact of their being shut 

 up and deprived of their liberty, or not, we do not 

 know, but they certainly will not breed. What an 

 astounding thing this is, to find one of the roost 

 important of all functions annihilated by mere 

 imprisonment ! 



So, again, there are cases known of animals 

 which have been thought by naturalists to be un- 

 doubted species, which have yielded perfectly fer- 

 tile hybrids ; while there are other species which 

 present what everybody believes to be varieties 1 



1 And as I conceive with very good reason ; but if any objec- 

 tor urges that we cannot prove that they have been produced by 



