if the influence of changed conditions "accumulates," it must be
through the inheritance of such modifications. Nor will I press the
question--What is the nature of the effect registered in the
reproductive elements, and which is subsequently manifested by
variations?--Is it an effect entirely irrelevant to the new requirements
of the variety?--Or is it an effect which makes the variety less fit for
the new requirements?--Or is it an effect which makes it more fit for
the new requirements? But not pressing these questions, it suffices to
point out the necessary implication that changed functions of organs
_do_, in some way or other, register themselves in changed proclivities
of the reproductive elements. In face of these facts it cannot be denied
that the modified action of a part produces an inheritable effect--be
the nature of that effect what it may.

The second of the remarks above adverted to as made by Mr. Darwin, is
contained in his sections dealing with correlated variations. In the
_Origin of Species_, p. 114, he says--

"The whole organization is so tied together during its growth and
development, that when slight variations in any one part occur, and
are accumulated through natural selection, other parts become
modified."

And a parallel statement contained in _Animals and Plants under
Domestication_, vol. ii, p. 320, runs thus--

"Correlated variation is an important subject for us; for when one
part is modified through continued selection, either by man or
under nature, other parts of the organization will be unavoidably
modified. From this correlation it apparently follows that, with
our domesticated animals and plants, varieties rarely or never
differ from each other by some single character alone."

By what process does a changed part modify other parts? By modifying
their functions in some way or degree, seems the necessary answer. It is
indeed, imaginable, that where the part changed is some dermal appendage
which, becoming larger, has abstracted more of the needful material from
the general stock, the effect may consist simply in diminishing the
amount of this material available for other dermal appendages, leading
to diminution of some or all of them, and may fail to affect in
appreciable ways the rest of the organism: save perhaps the
blood-vessels near the enlarged appendage. But where the part is an
active one--a limb, or viscus, or any organ