Chap. I. TJNDEK DOMESTICATION. 11 



similar changes of structure. Nevertheless some slight 

 amount of change may, I think, be attributed to the 

 direct action of the conditions of life — as, in some cases, 

 increased size from amount of food, colour from par- 

 ticular kinds of food and from light, and perhaps the 

 thickness of fur from climate. 



Habit also has a decided influence, as in the period 

 of flowering with plants when transported from one 

 climate to another. In animals it has a more marked 

 effect ; for instance, 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 I presume that this 

 change may be safely attributed to the domestic duck 

 flying much less, and walking more, than its wild parent. 

 The great and inherited development of the udders in 

 cows and goats in countries where they are habitually 

 milked, in comparison with the state of these organs 

 in other countries, is another instance of the effect of 

 use. Not a single domestic animal can be named 

 which has not in some country drooping ears ; and the 

 view suggested by some authors, that the drooping is due 

 to the disuse of the muscles of the ear, from the animals 

 not being much alarmed by danger, seems probable. 



There are many laws regulating variation, some few 

 of which can be dimly seen, and will be hereafter briefly 

 mentioned. I will here only allude to what may be 

 called correlation of growth. Any change in the embryo 

 or larva will almost certainly entail changes in the 

 mature animal. In monstrosities, the correlations be- 

 tween 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 instances of correlation are quite whimsical : thus 



