64 ARE THE EFFECTS OF USE INHERITED? 



slightly diminish the spread of the wings, and so 

 would affect the measurements taken. As the 

 wing-bones, moreover, are to some extent cor- 

 related with the beak and the feet, the artificial 

 selection of shortened beaks might tend to shorten 

 the wing as well as the feet. Under these 

 circumstances how can we be sure of the actual 

 efficacy of use-inheritance ? Surely selection is as 

 fully competent to effect slight changes in the 

 direction of use-inheritance as it undoubtedly is 

 to effect great changes in direct opposition to that 

 alleged factor of evolution. 



SHORTENED BREAST-BONE IN PIGEONS. 



The shortening of the sternum in pigeons is at- 

 tributed to disuse of the flight muscles attached to 

 it. The bone is only shortened by a third of an 

 inch, but this represents a very remarkable reduction 

 in proportional length, which Darwin estimates at 



