y ground. Will you think over this, and some time, either by
letter or when we meet, tell me what you think? Also, I want to know
whether your _female_ mimetic butterfly is more beautiful and brighter
than the male?

When next in London I must get you to show me your Kingfishers.

My health is a dreadful evil; I failed in half my engagements during
this last visit to London.--Believe me, yours very sincerely,

C. DARWIN.

* * * * *

The answer to this letter is missing, but in Vol. II. of "My Life," p.
3, Wallace writes:

"On reading this letter I almost at once saw what seemed to be a
very easy and probable explanation of the facts. I had then just
been preparing for publication (in the _Westminster Review_) my
rather elaborate paper on 'Mimicry and Protective Colouring,' and
the numerous cases in which specially showy and slow-flying
butterflies were known to have a peculiar odour and taste which
protected them from the attacks of insect-eating birds and other
animals led me at once to suppose that the gaudily coloured
caterpillars must have a similar protection. I had just
ascertained from Mr. Jenner Weir that one of our common white
moths (_Spilosoma menthastri_) would not be eaten by most of the
small birds in his aviary, nor by young turkeys. Now, as a _white_
moth is as conspicuous in the dusk as a coloured caterpillar in
the daylight, this case seemed to me so much on a par with the
other that I felt almost sure my explanation would turn out
correct. I at once wrote to Mr. Darwin to this effect."

* * * * *

_Down, Bromley, Kent, S.E. February 26, 1867._

My dear Wallace,--Bates was quite right, you are the man to apply to in
a difficulty. I never heard anything more ingenious than your
suggestion, and I hope you may be able to prove it true. That is a
splendid fact about the white moths; it warms one's very blood to see a
theory thus almost proved to be true.[57] With respect to the beauty of
male butterflies, I must as yet think that it is due to sexual
selection; there is some evidence that dragonflies are attracted by
bright colours; but what leads me to the above belief is so many male
Orthoptera and Cicadas having musical instruments. This being the case,
the analogy of birds makes me believe in sexual selection with respect
to colour in insects. I wish I had strength and