290 Colour and the Struggle for Life 
is well known that when the sexes differ the females are almost 
invariably more perfectly mimetic than the males and in a high 
proportion of cases are mimetic while the males are non-mimetic. 
The difficulty was met several years later by Fritz Miiller’s well- 
known theory, published in 18791, and immediately translated by 
Meldola and brought before the Entomological Society®. Darwin's 
letter to Meldola dated June 6, 1879, shows “that the first intro- 
duction of this new and most suggestive hypothesis into this country 
was due to the direct influence of Darwin himself, who brought it 
before the notice of the one man who was likely to appreciate it 
at its true value and to find the means for its presentation to English 
naturalists*.” Of the hypothesis itself Darwin wrote “F. Miiller’s 
view of the mutual protection was quite new to me*.” The hypo- 
thesis of Miillerian mimicry was at first strongly opposed. Bates 
himself could never make up his mind to accept it. As the Fellows 
were walking out of the meeting at which Professor Meldola explained 
the hypothesis, an eminent entomologist, now deceased, was heard to 
say to Bates: “It’s a case of save me from my friends!” The new 
ideas encountered and still encounter to a great extent the difficulty 
that the theory of Bates had so completely penetrated the literature 
of natural history. The present writer has observed that naturalists 
who have not thoroughly absorbed the older hypothesis are usually 
far more impressed by the newer one than are those whose allegiance 
has already been rendered. The acceptance of Natural Selection itself 
was at first hindered by similar causes, as Darwin clearly recognised: 
“If you argue about the non-acceptance of Natural Selection, it seems 
to me a very striking fact that the Newtonian theory of gravitation, 
which seems to every one now so certain and plain, was rejected by a 
man so extraordinarily able as Leibnitz. The truth will not penetrate 
a preoccupied mind°.” 
There are many naturalists, especially students of insects, who 
appear to entertain an inveterate hostility to any theory of mimicry. 
Some of them are eager investigators in the fascinating ‘field of 
geographical distribution, so essential for the study of Mimicry itself. 
The changes of pattern undergone by a species of Hrebia as we follow 
it over different parts of the mountain ranges of Europe is indeed 
a most interesting inquiry, but not more so than the differences 
between e.g. the Acraca johnstoni of S.E. Rhodesia and of Kiliman- 
jaro. A naturalist who is interested by the Hrebza should be equally 
interested by the Acraea; and so he would be if the student of 
1 Kosmos, May 1879, p. 100. 2 Proc. Ent. Soc. Lond. 1879, p. xx. 
* Charles Darwin and the Theory of Natural Selection, p. 214. 4 Ibid. p. 213. 
5 To Sir J. Hooker, July 28, 1868, More Letters, 1. p. 305. See also the letter to 
A. R. Wallace, April 30, 1868, in More Letters, 1. p. 77, lines 6—8 from top. 
