376 RUDIMENTARY, ATROPHIED, [CHAP. XIV. 



rudimentary teeth, which are subsequently absorbed, are beneficial 

 to the rapidly growing embryonic calf by removing matter so 

 precious as phosphate of lime? When a man's fingers have been 

 amputated, imperfect nails have been known to appear on the 

 stumps, and I could as soon believe that these vestiges of nails 

 are developed in order to excrete horny matter, as that the 

 rudimentary nails on the fin of the manatee have been developed 

 for this same purpose. 



On the view of descent with modification, the origin of rudi- 

 mentary organs is comparatively simple ; and we can understand 

 to a large extent the laws governing their imperfect development. 

 We have plenty of cases of rudimentary organs in our domestic 

 productions, as the stump of a tail in tailless breeds, the 

 vestige of an ear in earless breeds of sheep, the reappearance of 

 minute dangling horns in hornless breeds of cattle, more especially, 

 according to Youatt, in young animals, and the state of the 

 whole flower in the cauliflower. We often see rudiments of 

 various parts in monsters ; but I doubt whether any of these cases 

 throw light on the origin of rudimentary organs in a state of 

 nature, further than by showing that rudiments can be produced ; 

 for the balance of evidence clearly indicates that species under 

 nature do not undergo great and abrupt changes. But we learn 

 from the study of our domestic productions that the disuse of 

 parts leads to their reduced size ; and that the result is inherited. 



It appears probable that disuse has been the main agent in 

 rendering organs rudimentary. It would at first lead by slow 

 steps to the more and more complete reduction of a part, until at 

 last it became rudimentary, as in the case of the eyes of animals 

 inhabiting dark caverns, and of the wings of birds inhabiting 

 oceanic islands, which have seldom been forced by beasts of prey 

 to take flight, and have ultimately lost the power of flying. 

 Again, an organ, useful under certain conditions, might become 

 injurious under others, as with the wings of beetles living on 

 small and exposed islands ; and in this case natural selection will 

 have aided in reducing the organ, until it was rendered harmless 

 and rudimentary. 



Any change in structure and function, which can be effected by 

 small stages, is within the power of natural selection ; so that 

 an organ rendered, through changed habits of life, useless or 

 injurious for one purpose, might be modified and used for another 

 purpose. An organ might, also, be retained for one alone of its 

 former functions. Organs, originally formed by the aid of natural 

 selection, when rendered useless may well be variable, for their 

 variations can no longer be checked by natural selection. All 

 this agrees well with what we see under nature. Moreover, at 

 whatever period of life either disuse or selection reduces an 



