Chap. III. THEIR VARIATION. 77 



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 length may be due either to descent from a 

 distinct species or to more ancient domestication. The number 

 of mammae vary, as does the period of gestation. The latest 

 authority says' 21 that " the period averages from 17 to 20 

 weeks," but 1 think there must be some error in this state- 

 ment : in M. Tessier's observations on 25 sows it varied from 

 109 to 123 days. The Eev. W. D. Fox has given me ten 

 carefully recorded cases with well-bred pigs, in which the 

 period varied from 101 to 116 days. According to Nathusius 

 the period is shortest in the races which come early to ma- 

 turity ; but the course of their development does not appear 

 to be actually shortened, for the young animal is born, 

 judging from the state of the skull, less fully developed, or 

 in a mure embryonic condition, 22 than in the case of common 

 swine. In the highly cultivated and early matured races 

 the teeth, also, are developed earlier. 



The difference in the number of the vertebrae and ribs in 

 different kinds of pigs, as observed by Mr. Eyton, 23 and as 

 given in the following table, has often been quoted. The 

 African sow probably belongs to the S. scrofa type ; and Mr. 



19 ' Die Racen des Schweines,' s. 47. have been lost. I have added together 

 ' Schweineschadel,' s. 104. Compare, the dorsal and lumbar vertebrae, owing 

 also, the figures of the old Irish and to Prof. Owen's remarks (' Journal 

 the improved Irish breeds in Richard- Linn. Soc. vol. ii. p. 28) on the differ- 

 son on ' The Pig,' 1847. ence between dorsal and lumbar 



20 Quoted by Isid. Geoffroy, ' Hist. vertebras depending only on the 

 Nat. Gen.,' torn. iii. p 441. development of the ribs. Nevertheless 



21 S. Sidney, 'The Pig,' p. 61. the difference in the number of the 



22 ' Schweineschadel,' s. 2,20. ribs in pigs deserves notice. M. 



23 ' Proc. Zoolog. Soc.,' 1837, p. 23. Sanson gives the number of lumbar 

 I have not given the caudal vertebras, vertebras in various pigs; 'Coniptes 

 as Mr. Eyton says some might possibly Rendus,' lxiii. p. 843. 



