M THE ORIGIN OF SPECIES 



nearly the same restricted average range as have the 

 closely allied forms, marked for me by Mr. Watson as 

 doubtful species, but which are almost universally ranked 

 by British botanists as good and true species. 



/Summary 



Finally, varieties cannot be distinguished from species 

 — except, first, by the discovery of intermediate linking 

 forms; and, secondly, oy a certain indefinite amount of 

 diflierence between them; for two forms, if differing very 

 little, are generally ranked as varieties, notwithstanding 

 that they cannot be closely connected;! but the amount of 

 difference considered necessary to give to any two forms 

 the rank of species cannot be defined, i In genera having 

 more than the average number of species in any country, 

 the species of these genera have more than the average 

 number of varieties. In large genera the species are apt 

 to be closely, but unequally, allied together, forming little 

 clusters round other species. Species very closely allied 

 to other species apparently have restricted ranges. In 

 all these respects the species of large genera present 

 a strong analogy with varieties. And we can clearly 

 understand these analogies, if species once existed as 

 varieties, and thus originated; whereas, these analogies 

 are utterly inexplicable if species are independent cre- 

 ations. 



We have, also, seen that it is the most flourishing or 

 dominant species of the larger genera within each class 

 which on an average yield the greatest number of varie- 

 ties; and varieties, as we shall hereafter see, tend to 

 become converted into new and distinct species. Thus 

 the larger genera tend to become larger; and throughout 



