464 RECAPITULATION. 



of paramount importance 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 

 characters are often the most valuable of all. The real 

 affinities of all organic beings, in contra-distinction to their 

 adaptive resemblances, are due to inheritance or community 

 of descent. The Natural System is a genealogical arrange- 

 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 permanent char- 

 acters, 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 vertebrae 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 like- 

 wise, to a large extent, intelligible on the view of the grad- 

 ual 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 mam- 

 mals, 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 

 habits or conditions of life ; and we can understand on this 

 view the meaning of rudimentary organs. But disuse and 

 selection will generally act on each creature, when it has 

 come to maturity an<? has to play its full part in the strug- 

 gle for existence, an\ will thus have little power on an 

 organ during early 1 ¥e ; hence the organ will not be re- 

 duced or rendered rudimentary at this early age. The calf, 

 for instance, has inherited teeth, which never cut through 



