276 L^Y SERMONS, ADDRESSES, AND REVIEWS, [xii. 



fact, so far as the inquiry into the origin of species 

 goes, is, that there are such things in Nature as groups 

 of animals and of plants, whose members are incapable 

 of fertile union with those of other groups ; and that 

 there are such things as hybrids, which are absolutely 

 sterile when crossed with other hybrids. For if such 

 phenomena as these were exhibited by only two of those 

 assemblages of living objects, to which the name of 

 species (whether it be used in its physiological or in 

 its morphological sense) is given, it would have to be 

 accounted for by any theory of the origin of species, and 

 every theory which could not account for it would be, so 

 far, imperfect. 



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 theo- 

 retical views, no naturalist will probably 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, tend- 

 ing 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 hybridization 

 which are exhibited by many species when crossed with 

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



