Chap. XIV.] AND ABOETED OKGANS. 261 



ear in earless breeds of sheep, — tlie reappearance of 

 minute dancclincj 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 pro- 

 duced ; 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 reducinsr 

 the organ, until it was rendered harmless and rudi- 

 mentary. 



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 func- 



