DUCKS' LEGS AND WINGS. 59 



length. 1 The reduction in weight on which Darwin 

 relies seems to be entirely due to the shortening, 

 and this shortening appears to be irrelevant to 

 disuse, since the wings of the Call duck are simi- 

 larly shortened in their proportions by 12 per cent., 

 although this bird habitually flies to such an 

 extent that Darwin partly attributes the greatly 

 increased weight of its wing-bones to increased use 

 under domestication. 



We find that all the changes are in the 

 direction of shorter and thicker bones a tendency 

 which must be largely dependent upon the suspen- 

 sion of the rigorous elimination which keeps the 



1 This excessive thickening under disuse appears to be due partly 

 to a positive lateral enlargement or increase of proportional weight 

 of about 7^ per cent., and partly to a shortening of about 15 per 

 cent. Carefully calculated, the reduction of the weight of the wing- 

 bones in this breed is only 8*3 per cent, relatively to the whole 

 skeleton, or only 5 per cent, relatively to the skeleton minus legs 

 and wings. The latter method is the more correct, since the exces- 

 sive weight of the leg-bones increases the weight of the skeleton 

 more than the diminished weight of the wing-bones reduces it. 



