CONCLUBION. 495 



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 strug- 

 gle 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 procenitor 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 oa 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 inexplica- 

 ble is it that organs bearing the plain stamp of inutility, 

 such as the teeth in the embryonic calf or the shriveled 

 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 embryological and homologous 

 structures, but we are too blind to understand her 

 meaning. , 



I have now recapitulated the facts and considerations 

 which have thoroughly convinced me that species have been 

 modified, during a long course of descent. This has been 

 effected chiefly througli the natural selection of numerous 

 successive, slight, favorable variations ; aided in an impor- 

 tant manner by the inherited effects of the use and disuse 

 of parts; and in an unimportant manner, that is, in relation 

 to adaptive structures, whether past or present, by the 

 direct action of external conditions, and by variations 

 which seera to us in our ignorance to arise spontaneously. 

 It appears that I formerly underrated the frequency and 

 value of these latter forms of variation, as leading to per- 

 manent modifications of structure independently of natural 

 selection. But as my conclusions have lately been much 



