itive and
savage condition, induced by the act of crossing, as well as to the
unfavourable moral conditions under which they generally exist.

* * * * *

_Summary on the proximate causes leading to Reversion._--When purely-bred
animals or plants reassume long-lost characters,--when the common ass, for
instance, is born with striped legs, when a pure race of black or white
pigeons throws a slaty-blue bird, or when a cultivated heartsease with
large and rounded flowers produces a seedling with small and elongated
flowers,--we are quite unable to assign any proximate cause. When animals
run wild, the tendency to reversion, which, though it has been greatly
exaggerated, no doubt exists, is sometimes to a certain extent
intelligible. Thus, with feral pigs, exposure to the weather will probably
favour the growth of the bristles, as is known to be the case with the hair
of other domesticated animals, and through correlation the tusks will tend
to be redeveloped. But the reappearance of coloured longitudinal stripes on
young feral pigs cannot be attributed to the direct action of external
conditions. In this case, and in many others, we can only say that changed
habits of life apparently have favoured a tendency, inherent or latent in
the species, to return to the primitive state.

It will be shown in a future chapter that the position of flowers on the
summit of the axis, and the position of seeds within the capsule, sometimes
determine a tendency towards reversion; and this apparently depends on the
amount of sap or nutriment which the flower-buds and seeds receive. The
position, also, of buds, either on branches or on roots, sometimes
determines, as was formerly shown, the transmission of the {48} proper
character of the variety, or its reversion to a former state.

We have seen in the last section that when two races or species are crossed
there is the strongest tendency to the reappearance in the offspring of
long-lost characters, possessed by neither parent nor immediate progenitor.
When two white, or red, or black pigeons, of well-established breeds, are
united, the offspring are almost sure to inherit the same colours; but when
differently-coloured birds are crossed, the opposed forces of inheritance
apparently counteract each other, and the tendency which is inherent in
both parents to produce slaty-blue offspring becomes predominant. So it is
in several other cases. But when, for insta