Permanence and Evolution. 7 



of producing crosses of all grades of fertility, 

 from zero to perfect productiveness. It is owing 

 in great measure to the element of descent in 

 the conception of species that an importance is 

 attached to it different in kind from that be- 

 longing to the conceptions of family, order, etc. ; 

 species represents, it is said, a matter of fact, 

 the others are only arranged as a question of 

 convenience. Going on this principle, and no 

 rule being known for determining what differ- 

 ences are permanent and what not, when 

 dealing with wild animals, every, or almost 

 every, distinguishable race has been put down 

 as specifically distinct (A sinus onager and Hemip- 

 pus for example), and when dealing with 

 domestic animals, races are placed as of one 

 species, which, if wild, would have had no 

 chance of being so placed (the European and 

 Indian cow for example). 



It is to the credit of the evolutionists to 

 have done much to end this state of things ; 



