Chap. XV.] RECAPITULATION. 



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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 elassifieatory value; and why embryological char- 

 acters are often the most valuable of all. The real 

 afiinities 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, &e.; and we have to discover the lines of de- 

 scent 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 porpoise, and leg of the 

 horse, — the same number of vertebra 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 similarity 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 pis- 

 tils of a flower, is likewise, to a large extent, intelligible 

 on the view of the gradual modification of parts or or- 

 gans, which were aboriginally alike in an early progeni- 

 tor in each of these classes. On the principle of succes- 

 sive 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 

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