2SS LAWS OF VARIATION. Chap. XXIV. 



definite variability, that several generations mnst be subjected to 

 changed habits for any appreciable result. Our domestic fowls, 

 ducks, and geese have almost lost, not only in the individual but 

 in the race, their power of flight ; for we do not see a young fowl, 

 when frightened, take flight like a young pheasant. Hence I was 

 led carefully to compare the limb-bones of fowls, ducks, pigeons, 

 and rabbits, with the same bones in the wild parent-species. As 

 the measurements and weights were fully given in the earlier 

 chapters I need here only recapitulate the results. With domestic 

 pigeons, the length of the sternum, the prominence of its crest, 

 the length of the scapulae and furculum, the length of the wings as 

 measured from tip to tij> of the radii, are all reduced relatively to the 

 same parts in the wild pigeon. The wing and tail feathers, however, 

 are increased in length, but this may have as little connection with 

 the use of the wings or tail, as the lengthened hair on a dog with 

 the amount of exercise which it has habitually taken. The feet of 

 pigeons, except in the long-beaked races, are reduced in size. "With 

 fowls the crest of the sternum is less prominent, and is often dis- 

 torted or monstrous ; the wing-bones have become lighter relatively 

 to the leg-bones, and are apparently a little shorter in comparison 

 with those of the parent-form, the U alius bankiva. With ducks, 

 the crest of the sternum is affected in the same manner as in the 

 foregoing cases : the furculum, coracoids, and scapulae are all reduced 

 in weight relatively to the whole skeleton : the bones of the wings 

 are shorter and lighter, and the bones of the leg^ longer and heavier, 

 relatively to each other, and relatively to the whole skeleton, in 

 comparison with the same bones in the wild-duck. The decreased 

 weight and size of the bones, in the foregoing cases, is probably the 

 indirect result of the reaction of the weakened muscles on the bones. 

 I failed to compare the feathers of the wings of the tame and wild 

 duck; but Gloger 21 asserts that in the wild duck the tips of the 

 wing-feathers reach almost to the end of the tail, whilst in the 

 domestic duck they often hardly reach to its base. He remarks 

 also on the greater thickness of the legs, and says that the swimming 

 membrane between the toes is reduced ; but I was not able to 

 detect this latter difference. 



With the domesticated rabbit the body, together with the whole 

 skeleton, is generally larger and heavier than in the wild animal, 

 and the leg-bones are heavier in due proportion ; but whatever 

 standard of comparison be taken, neither the leg-bones nor the 

 scapulae have increased in length proportionally with the increased 

 dimensions of the rest of the skeleton. The skull has become in a 

 marked manner narrower, and, from the measurements of its 

 capacity formerly given, we may conclude, that this narrowness 

 results from the decreased size of the brain, consequent on the 

 mentally inactive life led by these closely-confined animals. 



We have seen in the eighth chapter that silk-moths, which have 



11 ' Das Ab'andern der Vogel,' 1833, s. 74. 



