36 DARWINIANA. 



ready to adopt the probable conclusion ; and we see 

 beforehand how strikingly the actual geographical 

 association of related species favors the broader view. 

 Whether we should continue to regard the forms in 

 question as distinct species, depends upon what mean- 

 ing we shall finally attach to that term ; and that de- 

 pends upon how far the doctrine of derivation can be 

 carried back and how well it can be supported. 



In applying his principle of natural selection to 

 the work in hand, Mr. Darwin assumes, as we have 

 seen: 1. Some variability of animals and plants in 

 nature ; 2. The absence of any definite distinction be- 

 tween slight variations, and varieties of the highest 

 grade ; 3. The fact that naturalists do not practically 

 agree, and do not increasingly tend to agree, as to what 

 forms are species and what are strong varieties, thus 

 rendering it probable that there may be no essential 

 and original difference, or no possibility of ascertain- 

 ing it, at least in many cases; also, 4. That the most 

 flourishing and dominant species of the larger genera 

 on an average vary most (a proposition which can be 

 substantiated only by extensive comparisons, the de- 

 tails of which are not given) ; and, 5. That in large 

 genera the species are apt to be closely but unequally 

 allied together, forming little clusters round certain 

 species just such clusters as would be formed if we 

 suppose their members once to have been satellites or 

 varieties of a central or parent species, but to have 

 attained at length a wider divergence and a specific 

 character. The fact of such association is undeniable ; 

 and the use which Mr. Darwin makes of it seems fair 

 and natural. 



