l selection. A review of Bates's theory of Mimicry was contributed
by Darwin to the "Natural History Review" (New Ser. Vol. III. 1863, page
219.) and an account of it is to be found in the "Origin" (Edition
1872, pages 375-378.) and in "The Descent of Man". (Edition 1874, pages
323-325.)

Darwin continually writes of the value of hypothesis as the inspiration
of inquiry. We find an example in his letter to Bates, Nov. 22, 1860:
"I have an old belief that a good observer really means a good theorist,
and I fully expect to find your observations most valuable." ("More
Letters", I. page 176.) Darwin's letter refers to many problems upon
which Bates had theorised and observed, but as regards Mimicry itself
the hypothesis was thought out after the return of the letter from the
Amazons, when he no longer had the opportunity of testing it by the
observation of living Nature. It is by no means improbable that, had
he been able to apply this test, Bates would have recognised that his
division of butterfly resemblances into two classes,--one due to
the theory of mimicry, the other to the influence of local
conditions,--could not be sustained.

Fritz Muller's contributions to the problem of Mimicry were all made
in S.E. Brazil, and numbers of them were communicated, with other
observations on natural history, to Darwin, and by him sent to Professor
R. Meldola who published many of the facts. Darwin's letters to Meldola
(Poulton, "Charles Darwin and the theory of Natural Selection", London,
1896, pages 199-218.) contain abundant proofs of his interest in
Muller's work upon Mimicry. One deeply interesting letter (Loc. cit.
pages 201, 202.) dated Jan. 23, 1872, proves that Fritz Muller before
he originated the theory of Common Warning Colours (Synaposematic
Resemblance or Mullerian Mimicry), which will ever be associated with
his name, had conceived the idea of the production of mimetic likeness
by sexual selection.

Darwin's letter to Meldola shows that he was by no means inclined to
dismiss the suggestion as worthless, although he considered it daring.
"You will also see in this letter a strange speculation, which I should
not dare to publish, about the appreciation of certain colours being
developed in those species which frequently behold other forms similarly
ornamented. I do not feel at all sure that this view is as incredible as
it may at first appear. Similar ideas have passed through my mind
when considering the dull colo