he tail, as usually happens when an
animal is born tailless, we can only explain by the strength of the
hereditary principle and by the period in embryo when affected{503}: but
on the theory of disuse gradually obliterating a part, we can see,
according to the principles explained in the last chapter (viz. of
hereditariness at corresponding periods of life{504}, together with the
use and disuse of the part in question not being brought into play in
early or embryonic life), that organs or parts would tend not to be
utterly obliterated, but to be reduced to that state in which they
existed in early embryonic life. Owen often speaks of a part in a
full-grown animal being in an "embryonic condition." Moreover we can
thus see why abortive organs are most developed at an early period of
life. Again, by gradual selection, we can see how an organ rendered
abortive in its primary use might be converted to other purposes; a
duck's wing might come to serve for a fin, as does that of the penguin;
an abortive bone might come to serve, by the slow increment and change
of place in the muscular fibres, as a fulcrum for a new series of
muscles; the pistil{505} of the marigold might become abortive as a
reproductive part, but be continued in its function of sweeping the
pollen out of the anthers; for if in this latter respect the abortion
had not been checked by selection, the species must have become extinct
from the pollen remaining enclosed in the capsules of the anthers.

{503} These words seem to have been inserted as an afterthought.

{504} _Origin_, Ed. i. p. 444, vi. p. 611.

{505} This and similar cases occur in the _Origin_, Ed. i. p. 452,
vi. p. 621.

Finally then I must repeat that these wonderful facts of organs formed
with traces of exquisite care, but now either absolutely useless or
adapted to ends wholly different from their ordinary end, being present
and forming part of the structure of almost every inhabitant of this
world, both in long-past and present times--being best developed and
often only discoverable at a very early embryonic period, and being full
of signification in arranging the long series of organic beings in a
natural system--these wonderful facts not only receive a simple
explanation on the theory of long-continued selection of many species
from a few common parent-stocks, but necessarily follow from this
theory. If this theory be rejected, these facts remain quite
inexplicable;