The nature of the food supplied during many generations has apparently affected the length of the intestines; for, according to Cuvier,[163] 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 { 74} length may be due either to descent from a distinct species or to more ancient domestication. The number of mammæ vary, as does the period of gestation. The latest authority says[164] that "the period averages from 17 to 20 weeks," but I think there must be some error in this statement: in M. Tessier's observations on 25 sows it varied from 109 to 123 days. The Rev. 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 maturity; but in these latter the course of 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 more embryonic condition,[165] than in the case of common swine, which arrive at maturity at a later age. In the highly cultivated and early matured races, the teeth, also, are developed earlier.
The difference in the number of the vertebræ and ribs in different kinds of pigs, as observed by Mr. Eyton,[166] and as given in the following table, has often been quoted. The African sow probably belongs to the _S. scrofa_ type; and Mr. Eyton informs me that, since the publication of his paper, cross-bred animals from the African and English races were found by Lord Hill to be perfectly fertile.
----------------+--------+---------+---------+-------------+----------- | English| | | | French | Long- | | | | Domestic | legged | African | Chinese | Wild Boar, | Boar, from | Male. | Female. | Male. | from Cuvier.| Cuvier. ----------------+--------+---------+---------+-------------+----------- Dorsal | | | | | vertebræ | 15 | 13 | 15 | 14 | 14 | | | | | Lumbar | 6 | 6 | 4 | 5 | 5 +--------+---------+---------+-------------+----------- Dorsal and | | | | | lumbar together | 21 | 19 | 19 | 19 | 19 | | | | | Sacral | 5 | 5 | 4 | 4 | 4 +--------+---------+---------+-------------+----------- Total number | | | | | of vertebræ | 26 | 24 | 23 | 23 | 23 ----------------+--------+---------+---------+-------------+-----------