mere rarity of variability in such a point was not sufficient, and I think
I concur with them. The fact of both the forms presenting the same case of
dimorphism is very curious. I have long wished that some one would dissect
the forms of the male stag-beetle with smaller mandibles, and see if they
were well developed, i.e., whether there was an abundance of spermatozoa;
and the same observations ought, I think, to be made on the rarer form of
your Cicada. Could you not get some observer, such as Dr. Hartman (453/2.
Mr. Walsh sent Mr. Darwin an extract from Dr. Hartman's "Journal of the
doings of a Cicada septendecim," in which the females are described as
flocking round the drumming males. "Descent of Man" (1901), page 433.), to
note whether the females flocked in equal numbers to the "drumming" of the
rarer form as to the common form? You have a very curious and perplexing
subject of investigation, and I wish you success in your work.


LETTER 454. TO A.R. WALLACE.
Down, June 15th [1869?].

You must not suppose from my delay that I have not been much interested by
your long letter. I write now merely to thank you, and just to say that
probably you are right on all the points you touch on, except, as I think,
about sexual selection, which I will not give up. My belief in it,
however, is contingent on my general belief in sexual selection. It is an
awful stretcher to believe that a peacock's tail was thus formed; but,
believing it, I believe in the same principle somewhat modified applied to
man.


LETTER 455. TO G.H.K. THWAITES.
Down, February 13th [N.D.]