£20 RECAPITULATION. [Chap. XV. 



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 modifica- 

 tions. 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 

 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 the em- 

 bryo 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 

 branch iaj. 



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 ace 

 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 believe, 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 cor- 

 responding 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 inexplic- 

 able 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 

 occur. Nature may be said to have taken pains to reveal her 

 scheme of modification, by means of rudimentary organs, of em- 



