Chap. V. ON THE EFFECTS OF DISUSE 185 



and small-sized breeds, and in all the scapula is proportionally 

 shorter (taking the same standard as before) than in the wild rock- 

 pigeon. The reduction in length on an average is very nearly one- 

 fiftli of an inch, or about one-ninth of the length of the scapula in 

 the rock-pigeon. 



The arms of the furcula in all the specimens which I compared, 

 diverged less, proportionally with the size of body, than in the rock- 

 pigeon; and the whole furculum was proportionally shorter. Thus 

 in a Eunt, whicli measured from tip to tip of wings 38i inches, the 

 furculum was only a very little longer (with the arms hardly more 

 divergent) than in a rock-pigeon which measured from tip to tip 

 26j inches. In a Barb, which in all its measurements was a little 

 larger than the sam.e rock-pigeon, the furculum was a quarter of an 

 inch shorter. In a Pouter, the furculum had not been lengthened 

 proportionally with the increased length of the body. In a Short- 

 faced Tumbler, wkich measured from tip to tip of wings 24 inches, 

 therefore only 2' inches less than the rock-pigeon, the furculum was 

 barely two-thirds of the length of that of the rock-pigeon. 



We thus clearly see that the sternum, scapulfe, and furculum 

 are all reduced in proportional length ; but when we turn to 

 the wings we find what at first appears a wholly different 

 and unexpected result. I may here remark that I have not 

 picked out specimens, hut have used every measurement made 

 by me. Taking the length from the base of beak to the end 

 of the tail as the standard of comparison, I find that, out of 

 thirty-five birds of various breeds, twenty-five have wings of 

 greater, and ten have them of less proportional length, than 

 in the rock-pigeon. But from the frequently correlated 

 length of the tail and wing-feathers, it is better to take as 

 the standard of comparison the length from the base of the 

 beak to the oil-gland ; and by this standard, out of twenty- 

 six of the same birds which had been thus measured, twenty- 

 one had wings too long, and only five had them too short. 

 In the twenty-one birds the wings exceeded in length those of 

 the rock-pigeon, on an average, by 1 3 inch ; whilst in the five 

 birds they were less in length by only -8 of an inch. As I was 

 much surprised that the wings of closely confined birds should 

 thus so frequently have been increased in length, it occurred 

 to me that it might be solely due to the greater length of the 

 wing-feathers ; for this certainly is the case with the Jacobin, 

 which has wings of unusual length. As in almost every case 

 I had measured the folded wings, I subtracted the length of 



