RECAPITULATION 801 



organic beings, in contradistinction to their adaptive re- 1 

 semblances, are due to inheritance or community of de- 

 scent. The Natural System is a oenealoo-ical arrange- i 

 ment, with the acquired grades of difference marked by \ 

 the terms varieties, species, genera, families, etc. ; and \ 

 we have to discover the lines of descent by the most j 

 permanent characters whatever they may be and of how- J 

 ever 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 vertebrae forming the neck of the 

 giraffe and of the elephant — and innumerable other such 

 facts, at once explain themselves on the theory of de- 

 scent with slow and slight successive modifications. The 

 similarity of pattern in the wing and in the leg of a 

 bat, though ased 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 earlyajgej^^and^ being in- 

 herited 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 the embryo of 

 an air-breathing mammal or bird having branchial slits 

 and arteries running in loops, like those of a fish which 

 has to breathe the air dissolved in water by the aid 

 of well-developed branchiae. 



Disuse, aided sometimes by natural selection, will often 

 have reduced organs when rendered useless under changed 



