50 THE ORIGIN OF SPECIES n 



Up to this point, we have been dealing with 

 matters of fact, and the statements which we 

 have laid before the reader would, to the best of 

 our knowledge, be admitted to contain a fair 

 exposition of what is at present known respecting 

 the essential properties of species, by all who 

 have studied the question. And whatever may 

 be his theoretical views, no naturalist will prob- 

 ably be disposed to demur to the following 

 summary of that exposition : 



Living beings, whether ' animals or plants, are 

 divisible into multitudes of distinctly definable 

 kinds, which are morphological species. They are 

 also divisible into groups of individuals, which 

 breed freely together, tending to reproduce their 

 like, and are physiological species. Normally 

 resembling their parents, the offspring of members 

 of these species are still liable to vary ; and the 

 variation may be perpetuated by selection, as a 

 race, which race, in many cases, presents all the 

 characteristics of a morphological species. But 

 it is not as yet proved that a race ever exhibits, 

 when crossed with another race of the same 

 species, those phenomena of hybridisation which 

 are exhibited by many species when crossed with 

 other species. On the other hand, not only is it 

 not proved that all species give rise to hybrids 

 infertile inter se, but there is much reason to 

 believe that, in crossing, species exhibit every 

 gradation from perfect sterility to perfect fertility. 



