VARIATION UNDER DOMESTICATION 11 



The great and inherited development of the udders in 

 eows 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 

 cats with blue eyes are invariably deaf; colour and 

 constitutional peculiarities go together, of which many 

 remarkable cases could be given amongst animals and 

 plants. From the facts collected by Heusinger, it ap- 

 pears that white sheep and pigs are differently affected 

 from coloured individuals by certain vegetable poisons. 

 Hairless dogs have imperfect teeth ; long-haired and 

 coarse-haired animals 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 unconsciously 

 modify other parts of the structure, owing to the 

 mysterious laws of the correlation of growth. 



The result of the various, quite unknown, or dimly 

 seen laws of variation is infinitely complex and 

 diversified. It is well worth while carefully to study 

 the several treatises published on some of our old 



