the females.), and afterwards to be inherited exclusively or more strongly by
the males. Finally, in accordance with the principle of inheritance as limited
by sex, the preservation and augmentation of secondary sexual characters in
natural species offers no especial difficulty, as this would follow through
that form of selection which I have called sexual selection.

INHERITANCE AT CORRESPONDING PERIODS OF LIFE.

This is an important subject. Since the publication of my 'Origin of Species'
I have seen no reason to doubt the truth of the explanation there given of one
of the most remarkable facts in biology, namely, the difference between the
embryo and the adult animal. The explanation is, that variations do not
necessarily or generally occur at a very early period of embryonic growth, and
that such variations are inherited at a corresponding age. As a consequence of
this the embryo, even after the parent-form has undergone great modification,
is left only slightly modified; and the embryos of widely-different animals
which are descended from a common progenitor remain in many important respects
like one another and probably like their common progenitor. We can thus
understand why embryology throws a flood of light on the natural system of
classification, as this ought to be as far as possible genealogical. When the
embryo leads an independent life, that is, becomes a larva, it has to be
adapted to the surrounding conditions in its structure and instincts,
independently of those of its parents; and the principle of inheritance at
corresponding periods of life renders this possible.

This principle is, indeed, in one way so obvious that it escapes attention. We
possess a number of races of animals and plants, which, when compared with one
another and with their parent-forms, present conspicuous differences, both in
their immature and mature states. Look at the seeds of the several kinds of
peas, beans, maize, which can be propagated truly, and see how they differ in