To B. D. Walsh   31 October 1868

My dear Sir

I am very much obliged for the extracts about the “drumming” which will be of real use to me.¹

I do not at all know what to think of your extraordinary cases of the cicadas.² Prof. Asa Gray & Dr Hooker were staying here & I told them of the facts.³ 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.⁴ 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.⁵ 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 D^r Hartman⁶ 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