adation in the
character of bees, especially in such important parts as the
mouth-organs, was altogether unknown to me. You bring out all such facts
very clearly by your comparison with the corresponding organs in the
allied hymenoptera. How very curious is the case of bees and wasps
having acquired, independently of inheritance from a common source, the
habit of building hexagonal cells and of producing sterile workers!
But I have been most interested by your discussion on secondary sexual
differences; I do not suppose so full an account of such differences in
any other group of animals has ever been published. It delights me
to find that we have independently arrived at almost exactly the
same conclusion with respect to the more important points deserving
investigation in relation to sexual selection. For instance, the
relative number of the two sexes, the earlier emergence of the males,
the laws of inheritance, etc. What an admirable illustration you give of
the transference of characters acquired by one sex--namely, that of the
male of Bombus possessing the pollen-collecting apparatus. Many of
your facts about the differences between male and female bees are
surprisingly parallel with those which occur with birds. The reading
your essay has given me great confidence in the efficacy of sexual
selection, and I wanted some encouragement, as extremely few naturalists
in England seem inclined to believe in it. I am, however, glad to find
that Prof. Weismann has some faith in this principle.

The males of Bombus follow one remarkable habit, which I think it would
interest you to investigate this coming summer, and no one could do
it better than you. (462/2. Mr. Darwin's observations on this curious
subject were sent to Hermann Muller, and after his death were translated
and published in Krause's "Gesammelte kleinere Schriften von Charles
Darwin," 1887, page 84. The male bees had certain regular lines of
flight at Down, as from the end of the kitchen garden to the corner of
the "sand-walk," and certain regular "buzzing places" where they stopped
on the wing for a moment or two. Mr. Darwin's children remember vividly
the pleasure of helping in the investigation of this habit.) I have
therefore enclosed a briefly and roughly drawn-up account of this habit.
Should you succeed in making any observations on this subject, and if
you would like to use in any way my MS. you are perfectly welcome. I
could, should you hereafter wish