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 any change in the
habits of life apparently favour 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 character proper to 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 instance, the ass is crossed with E.
indicus or with the horse--animals which have not striped legs--and the
hybrids have conspicuous stripes on their legs and even on their faces, all
that can be said is, that an inherent tendency to reversion is evolved through
some disturbance in the organisation caused by the act of crossing.

Another form of reversion is far commoner, indeed is almost universal with the