OF LIFE IN GENERAL. 333 



he ascribes certain of the changes in other domesticated 

 animals to a similar cause. Thus he found the length 

 of the sternum in eleven different breeds of domestic 

 pigeon to be on an average 13.0 per cent, shorter than 

 in the wild rock pigeon.* The crest of sternum, 

 scapulae, and furculum were also reduced in size, but 

 the wings were slightly increased, owing to the greater 

 length of the wing feathers. Again, in eight out of 

 the eleven breeds of fowl examined, the weight of 

 humerus and ulna, relative to that of femur and tibia, 

 was, on an average, 24.2 per cent, less than in the wild 

 Gallus bankiva, and in all eleven breeds the depth of 

 the crest of the sternum (to which the pectoral muscles 

 are attached), relative to its length, was diminished, 

 the average diminution being 17.5 per cent.f In the 

 case of the duck, Darwin weighed the entire skeleton, 

 as well as individual parts, and he found that whilst in 

 the four breeds of domestic duck examined the weight 

 of the femur, tibia, and tarsus, relative to that of the 

 body, was, on an average, 28.5 per cent, greater than in 

 the wild mallard, that of the humerus, radius, and meta- 

 carpus was 9.0 per cent. less.$ That this decrease in 

 the weight of the wing bones is the direct result of dis- 

 use was proved by the fact that in a domestic call duck 

 which was in the habit of constantly flying about for 

 miles, the relative weight of the wing bones was actu- 

 ally 12.1 per cent, greater than in the wild mallard. 



* "Animals and Plants," i. p. 184. 

 \Ibid. i. p. 285. J/W&, i. p. 301. 



