latter incubating, I have
gone a little into the subject and cannot say that I am fully satisfied.
I remember mentioning to you the case of Rhynchaea, but its nesting seems
unknown. In some other cases the difference in brightness seemed to me
hardly sufficiently accounted for by the principle of protection. At the
Falkland Islands there is a carrion hawk in which the female (as I
ascertained by dissection) is the brightest coloured, and I doubt
whether protection will here apply; but I wrote several months ago to
the Falklands to make inquiries. The conclusion to which I have been
leaning is that in some of these abnormal cases the colour happened to
vary in the female alone, and was transmitted to females alone, and that
her variations have been selected through the admiration of the male.

It is a very interesting subject, but I shall not be able to go on with
it for the next five or six months, as I am fully employed in correcting
dull proof-sheets; when I return to the work I shall find it much better
done by you than I could have succeeded in doing.

With many thanks for your very interesting note, believe me, dear
Wallace, yours very sincerely,

CH. DARWIN.

It is curious how we hit on the same ideas. I have endeavoured to show
in my MS. discussion that nearly the same principles account for young
birds _not_ being gaily coloured in many cases--but this is too complex
a point for a note.

_Postscript. Down. April 29._

My dear Wallace,--On reading over your letter again, and on further
reflection, I do not think (as far as I remember my words) that I
expressed myself _nearly strongly_ enough as to the value and beauty of
your generalisation, viz. that all birds in which the female is
conspicuously or brightly coloured build in holes or under domes. I
thought that this was the explanation in many, perhaps most cases, but
do not think I should ever have extended my view to your generalisation.
Forgive me troubling you with this P.S.--Yours,

CH. DARWIN.

* * * * *

_Down, Bromley, Kent, S.E. May 5, 1867._

My dear Wallace,--The offer of your valuable notes is _most_ generous,
but it would vex me to take so much from you, as it is certain that you
could work up the subject very much better than I could. Therefore I
earnestly and without any reservation hope that you will proceed with
your paper, so that I return your notes.

You seem already to have well investigated the