nd line of embryological research having been stopped. It was very
good of you to use your eyes in writing to me. I have just received your
essay (461/1. "Ueber der Einfluss der Isolirung auf die Artbildung":
Leipzig, 1872.); but as I am now staying in London for the sake of rest,
and as German is at all times very difficult to me, I shall not be able
to read your essay for some little time. I am, however, very curious to
learn what you have to say on isolation and on periods of variation.
I thought much about isolation when I wrote in Chapter IV. on the
circumstances favourable to Natural Selection. No doubt there remains
an immense deal of work to do on "Artbildung." I have only opened a path
for others to enter, and in the course of time to make a broad and clear
high-road. I am especially glad that you are turning your attention to
sexual selection. I have in this country hardly found any naturalists
who agree with me on this subject, even to a moderate extent. They think
it absurd that a female bird should be able to appreciate the splendid
plumage of the male; but it would take much to persuade me that the
peacock does not spread his gorgeous tail in the presence of the female
in order to fascinate or excite her. The case, no doubt, is much more
difficult with insects. I fear that you will find it difficult to
experiment on diurnal lepidoptera in confinement, for I have never heard
of any of these breeding in this state. (461/2. We are indebted to Mr.
Bateson for the following note: "This belief does not seem to be well
founded, for since Darwin's time several species of Rhopalocera (e.g.
Pieris, Pararge, Caenonympha) have been successfully bred in confinement
without any special difficulty; and by the use of large cages members
even of strong-flying genera, such as Vanessa, have been induced to
breed.") I was extremely pleased at hearing from Fritz Muller that he
liked my chapter on lepidoptera in the "Descent of Man" more than any
other part, excepting the chapter on morals.

LETTER 462. TO H. MULLER. Down [May, 1872].

I have now read with the greatest interest your essay, which contains
a vast amount of matter quite new to me. (462/1. "Anwendung der
Darwin'schen Lehre auf Bienen," "Verhandl. d. naturhist. Vereins fur
preuss. Rheinld. u. Westf." 1872. References to Muller's paper occur in
the second edition of the "Descent of Man.") I really have no criticisms
or suggestions to offer. The perfection of the gr