456 SUMMAEY. Chap. XIII. 



from presenting a strange difficulty, as they assuredly 

 do on the ordinary doctrine of creation, might even 

 have been anticipated, and can be accounted for by the 

 laws of inheritance. 



Summary. — In this chapter I have attempted to show, 

 that the subordination of group to group in all organisms 

 throughout all time ; that the nature of the relationship, 

 by which all living and extinct beings are united by 

 complex, radiating, and circuitous lines of affinities into 

 one grand system ; the rules followed and the difficulties 

 encountered by naturalists in their classifications ; the 

 value set upon characters, if constant and prevalent, 

 whether of high vital importance, or of the most trifling 

 importance, or, as in rudimentary organs, of no import- 

 ance ; the wide opposition in value between analogical 

 or adaptive characters, and characters of true affinity ; 

 and other such rules ; — all naturally follow on the view 

 of the common parentage of those forms which are con- 

 sidered by naturalists as allied, together with their modi- 

 fication through natural selection, with its contingencies 

 of extinction and divergence of character. In consider- 

 ing this view of classification, it should be borne in 

 mind that the element of descent has been universally 

 used in ranking together the sexes, ages, and acknow- 

 ledged varieties of the same species, however different 

 they may be in structure. If we extend the use of 

 this element of descent, — the only certainly known 

 cause of similarity in organic beings, — we shall under- 

 stand what is meant by the natural system : it is 

 genealogical in its attempted arrangement, with the 

 grades of acquired difference marked by the terms 

 varieties, species, genera, families, orders, and classes. 



On this same view of descent with modification, all 

 the great facts in Morphology become intelligible, — 



