ARGUMENTS FOR EVOLUTION 151

iadividnal development condensations or telescopings
of the presumed ancestral stages, and there may be
an Interpolation of developmental stages which are
adaptive to peculiar conditions of juvenile life and
have no historical import, but the deviations are such
as may be readily interpreted on the evolution-
hypothesis (Principles of Biology, I. pp. 450-467).

in. Arguments from Morphology. In back-boned
animals from frog to man there is a great variety of
fore-limb, adapted for running, swimming, flying,
grasping, and so forth, but throughout there is a
unity of structure and development. There are the
same fundamental bones and muscles, nerves and
blood vessels, and the early stages are closely similar.
So it is throughout organic nature ; there is unity of
type, maintained under extreme dissimilarities of form
and mode of life. This is " explicable as resulting
from descent with modification; but it is otherwise
inexplicable." "The likenesses disguised by unlike-
nesses, which the comparative anatomist discovers
between various organs in the same organism, are
worse than meaningless If it be supposed that
organisms were severally framed as we now see them 5
but they fit in quite harmoniously with the belief
that each kind of organism is a product of accumulated
modifications upon modifications. And the presence,
in all kinds of animals and plants, of functionally-
useless parts corresponding to parts that are function-
ally-useful in allied animals and plants, while it Is
totally incongruous with the belief in a construction
of each organism by miraculous interposition, is just
what we are led to expect by the belief that organisms
have arisen by progression." of scientific and trans-s intrinsic incoherence; worthless as