I am afraid I have caused you a great deal of trouble in writing to me at
such length. I am glad to say that I agree almost entirely with your
summary, except that I should put sexual selection as an equal, or perhaps
as even a more important agent in giving colour than Natural Selection for
protection. As I get on in my work I hope to get clearer and more decided
ideas. Working up from the bottom of the scale, I have as yet only got to
fishes. What I rather object to in your articles is that I do not think
any one would infer from them that you place sexual selection even as high
as No. 4 in your summary. It was very natural that you should give only a
line to sexual selection in the summary to the "Westminster Review," but
the result at first to my mind was that you attributed hardly anything to
its power. In your penultimate note you say "in the great mass of cases in
which there is great differentiation of colour between the sexes, I believe
it is due almost wholly to the need of protection to the female." Now,
looking to the whole animal kingdom, I can at present by no means admit
this view; but pray do not suppose that because I differ to a certain
extent, I do not thoroughly admire your several papers and your admirable
generalisation on birds' nests. With respect to this latter point,
however, although, following you, I suspect that I shall ultimately look at
the whole case from a rather different point of view.

You ask what I think about the gay-coloured females of Pieris. (443/1.
See "Westminster Review," July, 1867, page 37; also Letter 440.) I believe
I quite follow you in believing that the colours are wholly due to mimicry;
and I further believe that the male is not brilliant from not having
received through inheritance colour from the female, and from not himself
having varied; in short, that he has not been influenced by selection.

I can make no answer with respect to the elephants. With respect to the