his elaborate
display of it should be due merely to the vigour, activity, and vitality
of the male is to me as utterly incredible as my views are to you.
Mantegazza published a few years ago in Italy a somewhat similar view. I
cannot help doubting about recognition through colour; our horses, dogs,
fowls, and pigeons seem to know their own species, however differently
the individuals may be coloured. I wonder whether you attribute the
odoriferous and sound-producing organs, when confined to the males, to
their greater vigour, etc.? I could say a good deal in opposition to
you, but my arguments would have no weight in your eyes, and I do not
intend to write for the public anything on this or any other difficult
subject. By the way, I doubt whether the term voluntary in relation to
sexual selection ought to be employed: when a man is fascinated by a
pretty girl it can hardly be called voluntary, and I suppose that female
animals are charmed or excited in nearly the same manner by the gaudy
males.

Three essays have been published lately in Germany which would interest
you: one by Weismann, who shows that the coloured stripes on the
caterpillars of Sphinx are beautifully protective: and birds were
frightened away from their feeding-place by a caterpillar with large
eye-like spots on the broad anterior segments of the body. Fritz Mueller
has well discussed the first steps of mimicry with butterflies, and
comes to nearly or quite the same conclusion as you, but supports it by
additional arguments.

Fritz Mueller also has lately shown that the males alone of certain
butterflies have odoriferous glands on their wings (distinct from those
which secrete matter disgusting to birds), and where these glands are
placed the scales assume a different shape, making little tufts.

Farewell: I hope that you find Dorking a pleasant place? I was staying
lately at Abinger Hall, and wished to come over to see you, but driving
tires me so much that my courage failed.--Yours very sincerely,

CHAS. DARWIN.

* * * * *

_Madeira Villa, Madeira Road, Ventnor, Isle of Wight. September 3,
1877._

My dear Darwin,--Many thanks for your letter. Of course I did not expect
my paper to have any effect on your opinions. You have looked at all the
facts so long from your special point of view that it would require
conclusive arguments to influence you, and these, from the complex
nature of the question, are probably