[27] Variation of Animals and Plants under Domestication, i. 184, 185.
[28] Ibid., i. 144, 145.
[29] Ibid., i. 185.
[30] Variation of Animals and Plants under Domestication, i. 175.
[31] Variation of Animals and Plants under Domestication, i. 184. I suspect that Darwin was in poor health when he wrote this page. He nods at least four times in it. Twice he speaks of "twelve" breeds where he obviously should have said eleven.
[32] If a prominent breast is admired and selected by fanciers, the sternum might shorten in assuming a more forward and vertical position. If the shortening of the sternum is entirely due to disuse, it seems strange that Darwin has not noticed any similar shortening in the sternum of the duck. But selection has not tended to make the duck elegant, or "pigeon-breasted"; it has enlarged the abdominal sack instead, besides allowing the addition of an extra rib in various cases.
[33] Variation of Animals and Plants under Domestication, 144, 175.
[34] Variation of Animals and Plants under Domestication, i. 179.
[35] In the six largest breeds the shortening of the sternum is nearly twice as great as in the three smaller breeds which remain nearest the rock-pigeon in size. We can hardly suppose that use-inheritance especially affects the eight breeds that have varied most in size. If we exclude these, there is only a total shortening of 7 per cent. to be accounted for.
[36] Variation of Animals and Plants under Domestication, i. 183, 186.