298 



LAWS OF VARIATION. 



Chap. XXIV. 



only in the individual but in the race, their power of flight ; for we do 

 not see a chicken, 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 scapula} and 

 furcula, the length of the wings as measured from tip to tip of the radius 

 arc all reduced relatively to the same parts in the wild pigeon. 



in 



The wing 



w - ^ u~M.w T V^ CIO 



little connection with the use of the wings or tail, as the lengthened hair 

 on a dog with the amount of exercise which the breed 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 distorted or monstrous ; the wing-bones have become lighter rela- 

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

 with those of the parent-form, the Gall us bankiva. With ducks, the crest 

 of the sternum is affected in the same manner as in the foregoing cases : 

 the furcula, 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 legs longer and heavier, relatively to each other, and rela- 

 tively 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 mem- 

 brane 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 scapulas 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 mea- 

 surements of its capacity formerly given, we may conclude, that this nar- 

 rowness 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 been 

 kept during many centuries closely confined, emerge from their cocoons with 

 their wings distorted, incapable of flight, often greatly reduced in size, or 

 even, according to Quatrefages, quite rudimentary. This condition of the 

 wings may be largely owing to the same kind of monstrosity which often 

 affects wild Lepidoptera when artificially reared from the cocoon ; or it may 



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 Ik 



* Das Abandem der Vogel,' 1833, s. 74. . 



