Chap. I.] VARIATION UNDER DOMESTICATION. 13 



in countries where they are habitually milked, in com- 

 parison with these organs in other countries, is proba- 

 bly another instance of the effects of use. J^ot 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 St. Hilaire's great work on this 

 subject. Breeders believe that long limbs are almost 

 always accompanied by an elongated head. Some in- 

 stances of correlation are quite whimsical: thus cats 

 which are entirely white and have blue eyes are gen- 

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

 that this is confined to the males. Colour and con- 

 stitutional peculiarities go together, of which many re- 

 markable cases could be given amongst animals and 

 plants. From facts collected by Heusinger, it appears 

 that white sheep and pigs are injured by certain plants, 

 whilst dark-coloured individuals escape: Professor Wy- 

 man has recently communicated to me a good illustra- 

 tion 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 coloured their bones pink, and which caused the 

 hoofs of all but the black varieties to drop off; and one 



