50 THE ORIGIN OF SPECIES = | 
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 respectin 
the essential properties of species, by all wh 
have studied the question. And whatever ma 
be his theoretical views, no naturalist will prob- 
ably be disposed to demur to the — 
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 inier se, but there is much reason to 
believe that, in crossing, species exhibit every 
gradation from perfect sterility to perfect fertility. 
