472 RUDIMENTARY, ATROPHIED, 



mentary organs in our domestic productious, as the stump 

 of a tail in tailless breeds, the vestige of an ear in 

 earless breeds of sheep — the reappearance of minute dang- 

 ling 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 rudi- 

 ments 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 func- 

 tions. 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 selec- 

 tion. All this ascrees well with what we see under nature. 

 Moreover, at whatever period of life either disuse or selection 

 reduces an organ, and this will generally be when the being 

 has come to maturity and has to exert its full powers of 

 action, the principle of inheritance at corresponding ages 

 will t^nd to reproduce tki organ in its reduoed stat^ »t tJie 



