Chap. XV.] RECAPITULATION. 291 



are far more serviceable than others for classification ; — 

 why adaptive characters, though of paramount import- 

 ance to the beings, are of hardly any importance in 

 classification ; why characters derived from rudimentary 

 parts, though of no service to the beings, are often of 

 high classificatory value ; and why embryological char- 

 acters are often the most valuable of all. The real 

 affinities of all organic beings, in contradistinction to 

 their adaptive resemblances, are due to inheritance or 

 community of descent. The Natural System is a gene- 

 alogical arrangement, with the acquired grades of dif- 

 ference, marked by the terms, varieties, species, genera, 

 families, &c. ; and we have to discover the lines of 

 descent by the most permanent characters ■ whatever 

 they may be and of however slight vital importance. 



The similar framework of bones in the hand of a man, 

 wing of a bat, fin of the poipoise, and leg of the horse, 

 — the same number of vertebras forming the neck of the 

 giraffe and of the elephant, — and innumerable other such 

 facts, at once explain themselves on the theory of descent 

 with slow and slight successive modifications. The simi- 

 larity of pattern in the wing and in the leg of a bat, 

 though used for such different purpose, — in the jaws 

 and legs of a crab, — in the petals, stamens, and pistils 

 of a flower, is likewise; to a large extent, intelligible on 

 the view of the gradual modification of parts or organs, 

 which were aboriginally alike in an early progenitor in 

 each of these classes. On the principle of successive 

 variations not always supervening at an early age, and 

 being inherited at a corresponding not early period of 

 life, we clearly see why the embryos of mammals, birds, 

 reptiles, and fishes should be so closely similar, and so 

 unlike the adult forms. We may cease marvelling at 



