AND ABORTED ORGANS. 443 



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

 Jess breeds of sheep — the re-appearance of minute dan- 

 gling 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 sel- 

 dom been forced by beasts of pray 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 agrees 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 tend to reproduce the organ in its reduced state at the 

 same mature age, but will seldom affect it in the embryo. 

 Thus we can understand the greater size of rudimentary 

 organs in the embryo relatively, to the adjoining parts, and 



