; and the disdain is partially
inherited, for some young wild pigs bred in captivity showed an aversion
for this grain, whilst others of the same brood relished it.[751] One of my
relations bred some young pigs from {304} a Chinese sow by a wild Alpine
boar; they lived free in the park, and were so tame that they came to the
house to be fed; but they would not touch swill, which was devoured by the
other pigs. An animal when once accustomed to an unnatural diet, which can
generally be effected only during youth, dislikes its proper food, as
Spallanzani found to be the case with a pigeon which had been long fed on
meat. Individuals of the same species take to new food with different
degrees of readiness; one horse, it is stated, soon learned to eat meat,
whilst another would have perished from hunger rather than have partaken of
it.[752]

The caterpillars of the _Bombyx hesperus_ feed in a state of nature on the
leaves of the _Cafe diable_, but, after having been reared on the
Ailanthus, they would not touch the _Cafe diable_, and actually died of
hunger.[753]

It has been found possible to accustom marine fish to live in fresh water;
but as such changes in fish, and other marine animals, have been chiefly
observed in a state of nature, they do not properly belong to our present
subject. The period of gestation and of maturity, as shown in the earlier
chapters,--the season and the frequency of the act of breeding,--have all
been greatly modified under domestication. With the Egyptian goose the rate
of change in the season has been recorded.[754] The wild drake pairs with
one female, the domestic drake is polygamous. Certain breeds of fowls have
lost the habit of incubation. The paces of the horse, and the manner of
flight in certain breeds of the pigeon, have been modified, and are
inherited. The voice differs much in certain fowls and pigeons. Some breeds
are clamorous and others silent, as in the Call and common duck, or in the
Spitz and pointer dog. Every one knows how dogs differ from each other in
their manner of hunting, and in their ardour after different kinds of game
or vermin.

With plants the period of vegetation is easily changed and is inherited, as
in the case of summer and winter wheat, barley, {305} and vetches; but to
this subject we shall immediately return under acclimatisation. Annual
plants sometimes become perennial under a new climate, as I hear from Dr.
Hooker is the case with the stock and mign