ariations. He expresses his constant dread--one of the
troubles of his life--that his children would inherit his bad health.
It seems pretty clear, from what F. Darwin says in the new edition, that
Darwin's constant nervous stomach irritation was caused by his five
years sea-sickness. It was thoroughly established before, and in the
early years of, his marriage, and, on his own theory his children ought
all to have inherited it. Have they? You know perhaps better than I do,
whether any of the family show any symptoms of that particular form of
illness--and if not it is a fine case!--Yours very faithfully,

ALFRED R. WALLACE.

* * * * *

Wallace was formally admitted to the Royal Society in June, 1893. The
postscript of the following letter refers to his cordial reception by
the Fellows.

TO PROF. MELDOLA

_Parkstone, Dorset. June 10, 1893._

My dear Meldola,--As we had no time to "discourse" on Thursday, I will
say a few words on the individual adaptability question. We have to deal
with facts, and facts certainly show that, in many groups, there is a
great amount of adaptable change produced in the individual by external
conditions, and that that change is not inherited. I do not see that
this places Natural Selection in any subordinate position, because this
individual adaptability is evidently advantageous to many species, and
may itself have been produced or increased by Natural Selection. When a
species is subject to great changes of conditions, either locally or at
uncertain times, it may be a decided advantage to it to become
individually adapted to that change while retaining the power to revert
instantly to its original form when the normal conditions return. But
whenever the changed conditions are permanent, or are such that
individual adaptation cannot meet the requirements, then Natural
Selection rapidly brings about a permanent adaptation which is
inherited. In plants these two forms of adaptation are well marked and
easily tested, and we shall soon have a large body of evidence upon it.
In the higher animals I imagine that individual adaptation is small in
amount, as indicated by the fact that even slight varieties often breed
true.

In Lepidoptera we have the two forms of colour-adaptability clearly
shown. Many species are, in all their stages, permanently adapted to
their environment. Others have a certain power of individual adaptation,
as of the pupae to thei