10 VARIATION UNDER DOMESTICATION. 



nate importance in comparison with the nature of the 

 organism in determining each particular form of varia- 

 tion; perhaps of not more importance than the nature of 

 the spark, by which a mass of combustible matter is 

 ignited, has in determining the nature of the flames. 



EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS; 

 CORRELATED VARIATIO:?^; IIs^HERITANCE. 



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; 

 thas 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 prob- 

 ably 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 sug- 

 gested that the drooping is due to disuse of the muscles of 

 the ear, from t!.e animals being seldom much alarmed, 

 seems probable. 



Many laws regulate variation, some few of which can bo 

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

 here only allude to what may he called correlated variation. 

 Important changes in the embryo or larva will probablv 

 entail changes in the mature animal. In monstrosities, the 

 correlations between quite distinct parts are very curious; 

 and many instances are given in Isidore G-eoffroy 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; but it has been lately stated by Mr. Tait 

 that this is conflned to the males. Color and constitu- 

 tional pecularities go together, of which many remarkable 



