Chap. VIII. 



EFFECTS OF USE AND DISUSE. 



301 



namely, in one of the Call ducks, is in truth no exception, for this 

 bird was constantly in the habit of flying about ; and I have seen 

 it day after day rise from my grounds, and fly for a long time in 

 circles of more than a mile in diameter. In this Call duck there is 

 not only no decrease, but an actual increase in the weight of the 

 wing-bones relatively to those of the wild-duck ; and this probably 

 is consequent on the remarkable lightness and thinness of all the 

 bones of the skeleton. 



Lastly, I weighed the furculum, coracoids, and scapula of a wild 

 duck and of a common domestic duck, and I found that their 

 weight, relatively to that of the whole skeleton, was as one hundred 

 in the former to eighty-nine in the latter ; this shows that these 

 bones in the domestic duck have been reduced eleven per cent, of 

 their due proportional weight. The prominence of the crest of the 

 sternum, relatively to its length, is also much reduced in all the 

 domestic breeds. These changes have evidently been caused by 

 the lessened use of the wings. 



It is well known that several birds, belonging to different 

 Orders, and inhabiting oceanic islands, have their wings 

 greatly reduced in size and are incapable of flight. I sug- 

 gested in my ' Origin of Species ' that, as these birds are not 



