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Letter 6437

Darwin, C. R. to Walsh, B. D.

31 Oct 1868

    Summary Add

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    Thanks BDW for extracts about "drumming" [of male Cicada to attract females].

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    Asa Gray and Hooker doubt that 13–year and 17–year Cicada forms should be considered distinct species. CD is inclined to agree with them.

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    Suggests observations be made of ratio of females to males in the rarer form.

Transcription

Down. | Bromley. | Kent. S.E.

Oct 31. 1868

My dear Sir

I am very much obliged for the extracts about the ``drumming'' which will be of real use to me.

I do not at all know what to think of your extraordinary cases of the cicadas. Prof. Asa Gray & Dr Hooker were staying here & I told them of the facts. They thought that the 13-year & the 17-year forms ought not to be ranked as distinct species unless other differences besides the period of development could be discovered. They thought the mere rarity of variability in such a point was not sufficient, & 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 to see if they were well developed, i.e. whether there was an abundance of spermatozoa, & 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 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 & perplexing subject of investigation & I wish you success in your work—

My dear Sir | yours very sincerely | Charles Darwin

    Footnotes Add

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    f1 6437.f1
    For one of the extracts sent by Walsh, see the memorandum from B. D. Walsh, [before 31 October 1868].
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    f2 6437.f2
    See letter from B. D. Walsh, 29 August 1868. CD also commented on the cicadas in his letter to Walsh of 21 September 1868.
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    f3 6437.f3
    A group of guests, including Asa Gray and Joseph Dalton Hooker, stayed at Down House from October 24 (see letter to John Tyndall, 20 October 1868 and n. 1).
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    f4 6437.f4
    Walsh had described another difference between the two cicada forms in the shape of the genital hooklet (see letter from B. D. Walsh, 29 August 1868).
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    f5 6437.f5
    No letter from Walsh containing such a reference to dimorphism has been found.
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    f6 6437.f6
    CD refers to William Dell Hartman (see memorandum from B. D. Walsh, [before 31 October 1868]).
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