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.
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