264: SUMMARY. [Chap. XIv" 



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 con- 

 stant and prevalent, whether of high or of the most tri- 

 fling importance, or, as with rudimentary organs, of no 

 importance, — the wide opposition in value between an- 

 alogical or adaptive characters, and characters of true 

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

 we admit the common parentage of allied forms, to- 

 gether with their modification through variation and 

 natural selection, with the contingencies of extinction 

 and divergence of character. In considering this view 

 of classification, it should be borne in mind that the ele- 

 ment of descent has been universally used in ranking to- 

 gether the sexes, ages, dimorphic forms, and acknowl- 

 edged 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 



