518 ORIGIN OF SPECIES 



tern 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 modi- 

 fication 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-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 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 in- 

 stance, 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 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 inexplicable is it that 

 organs bearing the plain stamp of inutility, such as the teeth 

 in the embryonic calf or the shrivelled wings under the sol- 

 dered 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. 



