THE LAWS OF VARIABILITY. 49 



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. 



From facts collected by Heusinger, it ap- 

 pears 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 pig3 ate the paint-root (Lach- 

 nanthes), 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 rais- 

 ing, as they alone have a good chance of living." Hair- 

 less 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 be- 

 tween 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 agmenting, any pe- 

 culiarity, he will almost certainly modify unintentionally 

 other parts of the structure, owing to the mysterious laws 

 of correlation. 



