possible examples of reversion; and they are
intelligible on the belief that characters common to the grandparent and
grandchild of the same sex are present, though latent, in the intermediate
parent of the opposite sex.

The subject of latent characters is so important, as we shall see in a
future chapter, that I will give another illustration. {53} Many animals
have the right and left sides of their body unequally developed: this is
well known to be the case with flat-fish, in which the one side differs in
thickness and colour, and in the shape of the fins, from the other; and
during the growth of the young fish one eye actually travels, as shown by
Steenstrup, from the lower to the upper surface.[122] In most flat-fishes
the left is the blind side, but in some it is the right; though in both
cases "wrong fishes," which are developed in a reversed manner to what is
usual, occasionally occur, and in _Platessa flesus_ the right or left side
is indifferently developed, the one as often as the other. With gasteropods
or shell-fish, the right and left sides are extremely unequal; the far
greater number of species are dextral, with rare and occasional reversals
of development, and some few are normally sinistral; but certain species of
Bulimus, and, many Achatinellae,[123] are as often sinistral as dextral. I
will give an analogous case in the great Articulate kingdom: the two sides
of Verruca[124] are so wonderfully unlike, that without careful dissection
it is extremely difficult to recognise the corresponding parts on the
opposite sides of the body; yet it is apparently a mere matter of chance
whether it be the right or the left side that undergoes so singular an
amount of change. One plant is known to me[125] in which the flower,
according as it stands on the one or other side of the spike, is unequally
developed. In all the foregoing cases the two sides of the animal are
perfectly symmetrical at an early period of growth. Now, whenever a species
is as liable to be unequally developed on the one as on the other side, we
may infer that the capacity for such development is present, though latent,
in the undeveloped side. And as a reversal of development occasionally
occurs in animals of many kinds, this latent capacity is probably very
common.

The best yet simplest instances of characters lying dormant are, perhaps,
those previously given, in which chickens and {54} young pigeons, raised
from a cross between differently