Changed habits produce an inherited effect, as in the period of the flowering of plants when transported from one climate to another. With animals the increased use or disuse of parts has had a more marked influence; thus I find in the domestic duck that the bones of the wing weigh less and the bones of the leg more, in proportion to the whole skeleton, than do the same bones in the wild-duck; and this change may be safely attributed to the domestic duck flying much less, and walking more, than its wild parents. The great and inherited development of the udders in cows and goats in countries where they are habitually milked, in comparison with these organs in other countries, is probably another instance of the effects of use. Not one of our domestic animals can be named which has not in some country drooping ears; and the view which has been suggested that the drooping is due to the disease of the muscles of the ear, from the animals being seldom much alarmed, seems probable. * * * * * [Page 9.] From facts collected by Heusinger, it appears that white sheep and pigs are injured by certain plants, while dark-colored individuals escape, Professor Wyman has recently communicated to me a good illustration of this fact: on asking some farmers in Virginia how it was that all their pigs were black, they informed him that the pigs ate the paint-root (_Lachnanthes_), which colored their bones pink, and which caused the hoofs of all but the black varieties to drop off; and one of the “crackers” (i. e., Virginia squatters) added, “We select the black members of a litter for raising, as they alone have a good chance of living.” Hairless dogs have imperfect teeth; long-haired and coarse-haired animals are apt to have, as is asserted, long or many horns; pigeons with feathered feet have skin between their outer toes; pigeons with short beaks have small feet, and those with long beaks large feet. Hence, if man goes on selecting, and thus augmenting, any peculiarity, he will almost certainly modify unintentionally other parts of the structure, owing to the mysterious laws of correlation. EFFECTS OF THE USE AND DISUSE OF PARTS. [Origin of Species, page 108.]