ly 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.[162]

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 mammae
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 vertebrae 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 | | | |