PIGEON'S BREAST-BONE. 65 



from one-seventh to one-eighth, or over 13 per 

 cent. This marked reduction, too, quite unlike 

 the slight reduction of the wing-bones to which 

 the other ends of the muscles are attached, was 

 universal in* the eleven specimens measured by 

 Darwin ; and the bone, though acknowledged 

 to have been modified by artificial selection 

 in some breeds, is not so open to observation as 

 wings or legs. Even, however, if this relative 

 shortening of the sternum remained otherwise 

 inexplicable, it might still be as irrelevant to use 

 and disuse as is the fact that " many breeds " 

 of fancy pigeons have lost a rib, having only 

 seven where the ancestral rock-pigeon has eight. 1 

 But the excessive reduction in the sternum is 

 far from being inexplicable. In the first place 

 Darwin has somewhat over-estimated it. Instead 

 of comparing the deficiency of length with the 

 increased length which should have been acquired 



1 Variation of Animals and Plants under Domestication, i. 175. 



F 



