anner in which the
cast-off atoms or so-called gemmules probably act (225/4. "Assuming
the general truth of the theory that molecules endowed with certain
attributes are cast off by the component cells of such infinitesimal
minuteness as to be capable of circulating with the fluids, and in the
end to be present in the unimpregnated embryo-cell and spermatozoid...it
seems to me far more probable that they should be capable under
favourable circumstances of exercising an influence analogous to that
which is exercised by the contents of the pollen-tube or spermatozoid on
the embryo-sac or ovum, than that these particles should be themselves
developed into cells" (Berkeley, page 87).): I have never supposed that
they were developed into free cells, but that they penetrated other
nascent cells and modified their subsequent development. This process
I have actually compared with ordinary fertilisation. The cells thus
modified, I suppose cast off in their turn modified gemmules, which
again combine with other nascent cells, and so on. But I must not
trouble you any further.

LETTER 226. TO AUGUST WEISMANN. Down, October 22nd, 1868.

I am very much obliged for your kind letter, and I have waited for a
week before answering it in hopes of receiving the "kleine Schrift"
(226/1. The "kleine Schrift" is "Ueber die Berechtigung der Darwin'schen
Theorie," Leipzig, 1868. The "Anhang" is "Ueber den Einfluss der
Wanderung und raumlichen Isolirung auf die Artbilding.") to which you
allude; but I fear it is lost, which I am much surprised at, as I have
seldom failed to receive anything sent by the post.

As I do not know the title, and cannot order a copy, I should be very
much obliged if you can spare another.

I am delighted that you, with whose name I am familiar, should approve
of my work. I entirely agree with what you say about each species
varying according to its own peculiar laws; but at the same time it
must, I think, be admitted that the variations of most species have in
the lapse of ages been extremely diversified, for I do not see how it
can be otherwise explained that so many forms have acquired analogous
structures for the same general object, independently of descent. I am
very glad to hear that you have been arguing against Nageli's law of
perfectibility, which seems to me superfluous. Others hold similar
views, but none of them define what this "perfection" is which cannot
be gradually attained through Natural Sel