VARIATION UNDER DOMESTICATION 29 



producing moss-roses — we clearly see that the nature of the 

 condition is of subordinate importance in comparison with 

 the nature of the organism in determining each particular 

 form of variation — 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 VARIATION; INHERITANCE 



Changed habits produce an inherited efifect, as in the pe- 

 riod of the flowering of plants when transported from one 

 climate to another. With animals the increased use or dis- 

 use of parts has had a more marked influence; thus 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 skele- 

 ton, 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 com- 

 parison with these organs in other countries, is probably 

 another instance of the effects of use. Not one of our do- 

 mestic 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 en- 

 tail changes in the mature animal. In monstrosities, the 

 correlations between quite distinct parts are very curious; 

 and many instances are given in Isidore Geoff 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 ; but it has been lately stated by Mr. Tait that 

 this is confined to the males. Colour and constitutional pecu- 



