26 VAKIATION Chap. I. 



in cows and goats in countries where they arc habitually milked, 

 in comparison with the state of these organs in other coimtries, 

 is probably another instance of the cfl'ects 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 disuse of the muscles of the 

 ear, from the animals being seldom alarmed by danger, seems 

 probable. 



^lany 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. Im- 

 portant changes in the embryo or larva will probably entail 

 changes in the mature animal. In monstrosities, the correla- 

 tions between quite distinct parts are very curiovis ; and many 

 instances are given in Isidore Geofl'roy St.-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. Color and coii- 

 stitutional peculiarities go together, of which many remarkable 

 cases could be given among animals and plants. From facts 

 collected by Heusinger, it appears that white sheep and pigs 

 are injured by certain plants, while dark-colored mdii-iduals es- 

 cape : Prof. Wyman has recently communicated to me a good 

 illustration of this fact ; on asking some farmers in Florida 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., Florida 

 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 ani- 

 mals 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 imintentionally other parts of the structure, owing to 

 tlie mysterigus laws of correlation. 



The results of the various, unknown, or but dimly under- 

 stood laws of variation are infinitely complex and diversified. 

 It is well worth Avhile can-fiilly to study the several treatises 

 on some of our ol<l cultivated jilants, as on tlie ]iyaci:ith, potato. 



