Chap. XIX. HYBRIDISM. 175 



the inhabitants of the same country distinct, be thought of 

 such paramount importance, in comparison with other inci- 

 dental and functional differences ? No sufficient answer to 

 this question can be given. Hence the fact that widely 

 distinct domestic varieties are, with rare exceptions, perfectly 

 fertile when crossed, and produce fertile offspring, whilst 

 closely allied species are, with rare exceptions, more or less 

 sterile, is not nearly so formidable an objection as it appears 

 at first to the theory of the common descent of allied species. 



