Chap. III. THEIR VARIATION. 73 



affect the skull ; but it seems rather doubtful how far this will 

 account for the greatly reduced length of the skull and for 

 its concave front. It is well known (Nathusius himself ad- 

 vancing many cases, s. 104) that there is a strong tendency in 

 many domestic animals — in bull- and pug- dogs, in the niata 

 cattle, in sheep, in Polish fowls, short-faced tumbler pigeons, and 

 in one variety of the carp — for the bones of the face to become 

 greatly shortened. In the case of the dog, as H. Miiller has 

 shown, this seems caused by an abnormal state of the primordial 

 cartilage. We may, however, readily admit that abundant and 

 rich food supplied during many generations would gi\e an in- 

 herited tendency to increased size of body, and that, from disuse, 

 the limbs would become finer and shorter. 18 We shall in a 

 future chapter also see that the skull and limbs are apparently 

 in some manner correlated, so that any change in the one tends 

 to affect the other. 



Nathusius has remarked, and the observation is an interesting 

 one, that the peculiar form of the skull and body in the most 

 highly cultivated races is not characteristic of any one race, but 

 is common to all when improved up to the same standard. 

 Thus the large-bodied, long-eared, English breeds with a convex 

 back, and the small-bodied, short-eared, Chinese breeds with a 

 concave back, when bred to the same state of perfection, nearly 

 resemble each other in the form of the head and body. This 

 result, it appears, is partly due to similar causes of change acting 

 on the several races, and partly to man breeding the pig for one 

 sole purpose, namely, for the greatest amount of flesh and fat ; 

 so that selection has always tended towards one and the same 

 end. With most domestic animals the result of selection has 

 been divergence of character, here it has been convergence. 19 



The nature of the food supplied during many generations has 

 apparently affected the length of the intestines ; for, according 

 to Cuvier, 20 their length to that of the body in the wild boar 

 is as 9 to 1,— in the common domestic boar as 13'5 to 1,— and 

 in the Siam breed as 16 to 1. In this latter breed the greater 



w Nathusius ■ Die Racen des improved Irish breeds in Richardson 



Schwemes, s. 71. on ' The Pig ' 1847 



» < Die Racen des Schweines,' s. 47. 20 Q uote d'by Isld. Geoffroy, 'Hist. 



' Schwemeschadel, s. 104. Compare, Nat. Gen.,' torn. iii. p. 441. 

 also, the figures of the old Irish and the 



