I think, clearly see why
embryological characters are of such high classificatory importance.
Geographical distribution may sometimes be brought usefully into play in
classing large and widely-distributed genera, because all the species of
the same genus, inhabiting any distinct and isolated region, have in all
probability descended from the same parents.

We can understand, on these views, the very important distinction
between real affinities and analogical or adaptive resemblances.
Lamarck first called attention to this distinction, and he has been ably
followed by Macleay and others. The resemblance, in the shape of the
body and in the fin-like anterior limbs, between the dugong, which is a
pachydermatous animal, and the whale, and between both these mammals and
fishes, is analogical. Amongst insects there are innumerable instances:
thus Linnaeus, misled by external appearances, actually classed an
homopterous insect as a moth. We see something of the same kind even
in our domestic varieties, as in the thickened stems of the common and
swedish turnip. The resemblance of the greyhound and racehorse is hardly
more fanciful than the analogies which have been drawn by some authors
between very distinct animals. On my view of characters being of real
importance for classification, only in so far as they reveal descent, we
can clearly understand why analogical or adaptive character, although of
the utmost importance to the welfare of the being, are almost valueless
to the systematist. For animals, belonging to two most distinct lines
of descent, may readily become adapted to similar conditions, and thus
assume a close external resemblance; but such resemblances will not
reveal--will rather tend to conceal their blood-relationship to their
proper lines of descent. We can also understand the apparent paradox,
that the very same characters are analogical when one class or order is
compared with another, but give true affinities when the members of the
same class or order are compared one with another: thus the shape of
the body and fin-like limbs are only analogical when whales are compared
with fishes, being adaptations in both classes for swimming through the
water; but the shape of the body and fin-like limbs serve as characters
exhibiting true affinity between the several members of the whale
family; for these cetaceans agree in so many characters, great and
small, that we cannot doubt that they have inherited their gene