10 VARIATION UNDER DOMESTICATION. 



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 disuse of the muscles 

 of the ear, from the animals being seldom much alarmed, 

 seems probable. 



Many laws regulate variation, some few of which can be 

 dimly seen, and will hereafter be briefly discussed. I will 

 here only allude to what may be called correlated variation. 

 Important changes in the embryo or larva will probably 

 entail changes in the mature animal. In monstrosities, the 

 correlations between quite distinct parts are very curious ; 

 and many instances are given in Isidore Geoffroy Saint 

 Hilaire's great work on this subject. Breeders believe that 

 long limbs are almost always accompanied by an elongated 

 head. Some instances of correlation are quite whimsical ; 

 thus cats which are entirely white and have blue eyes are 

 generally deaf; but it has been lately stated by Mr. Tait 

 that this is confined to the males. Color and constitutional 

 peculiarities go together, of which many remarkable cases 

 could be given among animals and plants. From facts col- 

 lected 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 hoof's 

 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. 



