nd, and then at certain moles, which are habitually blind and have
their eyes covered with skin; or when we look at the blind animals
inhabiting the dark caves of America and Europe. In both varieties and
species correlation of growth seems to have played a most important
part, so that when one part has been modified other parts are
necessarily modified. In both varieties and species reversions to
long-lost characters occur. How inexplicable on the theory of creation
is the occasional appearance of stripes on the shoulder and legs of the
several species of the horse-genus and in their hybrids! How simply is
this fact explained if we believe that these species have descended from
a striped progenitor, in the same manner as the several domestic breeds
of pigeon have descended from the blue and barred rock-pigeon!

On the ordinary view of each species having been independently created,
why should the specific characters, or those by which the species of
the same genus differ from each other, be more variable than the generic
characters in which they all agree? Why, for instance, should the colour
of a flower be more likely to vary in any one species of a genus, if
the other species, supposed to have been created independently, have
differently coloured flowers, than if all the species of the genus have
the same coloured flowers? If species are only well-marked varieties,
of which the characters have become in a high degree permanent, we can
understand this fact; for they have already varied since they branched
off from a common progenitor in certain characters, by which they have
come to be specifically distinct from each other; and therefore these
same characters would be more likely still to be variable than the
generic characters which have been inherited without change for an
enormous period. It is inexplicable on the theory of creation why a part
developed in a very unusual manner in any one species of a genus,
and therefore, as we may naturally infer, of great importance to the
species, should be eminently liable to variation; but, on my view, this
part has undergone, since the several species branched off from a common
progenitor, an unusual amount of variability and modification, and
therefore we might expect this part generally to be still variable. But
a part may be developed in the most unusual manner, like the wing of a
bat, and yet not be more variable than any other structure, if the part
be common to many sub