RECAPITULATION AND CONCLUSION 429 



etc.; 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 m the hand of a man, wing 

 of a bat, fin of the porpoise, and leg of the horse — the same num- 

 ber of vertebrae forming the neck of the giraffe and of the ele- 

 phant — and innumerable other such facts, at once explain them- 

 selves 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 pistils of a flower, 

 is likewise, 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 prin- 

 ciple 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 the embryo of an air-breath- 

 ing mammal or bird having branchial slits and arteries running 

 in loops, like those of a fish which has to breathe the air dis- 

 solved 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 mean- 

 ing of rudimentary organs. But disuse and selection will generally 

 act on each creature, when it has come to maturity and has to 

 play its full part in the struggle for existence, and will thus have 

 little power on an organ during early life; hence the organ will 

 not be reduced or rendered rudimentary at this early age. The 

 calf, for instance, has inherited teeth, which never cut through 

 the gums of the upper jaw, from an early progenitor having well- 

 developed teeth ; and we may beheve, that the teeth in the mature 

 animal were formerly reduced by disuse, owing to the tongue and 

 palate, or lips, having become excellently fitted through natural 

 selection to browse without their aid; whereas in the calf, the 

 teeth have been left unaffected, and on the principle of inheritance 

 at corresponding ages have been inherited from a remote period 

 to the present day. On the view of each organism with all its 

 separate parts having been specially created, how utterly inex- 

 plicable is it that organs bearing the plain stamp of inutility, such 

 as the teeth in the embryonic calf, or the shrivelled wings under 

 the soldered wing-covers of many beetles, should so frequently 



