264 SUMMAEY. [Chap. XIY. 



Summary, 



In this chapter I have attempted to show, that the 

 arrangement of all organic beings throughout all time 

 in groups under groups — that the nature of the relation- 

 ships by which all living and extinct organisms are 

 united by complex, radiating, and circuitous lines of 

 affinities into a few grand classes, — the rules followed 

 and the difficulties encountered by naturalists in their 

 classifications, — the value set upon characters, if constant 

 and prevalent, whether of high or of the most trifling 

 importance, or, as with rudimentary organs, of no 

 importance, — the wide opposition in value between 

 analogical or adaptive characters, and characters of true 

 affinity ; and other such rules ; — all naturally follow if 

 we admit the common parentage of allied forms, together 

 with their modification through variation and natural 

 selection, with the contingencies of extinction and di- 

 vergence of character. In considering this view of classifi- 

 cation, it should be borne in mind that the element of 

 descent has been universally used in ranking together 

 the sexes, ages, dimorphic forms, and acknowledged 

 varieties of the same species, however much they may 

 differ from each other in structure. If we extend the 

 use of this element of descent, — the one certainly 

 known cause of similarity in organic beings, — we shall 

 understand 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, most 



