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Darwin Correspondence Project

To Fritz Müller   8 September [1869]1

Down. | Beckenham | Kent. S.E.

Sept. 8

My dear Sir

I write now to ask you to observe the Papilio or Peridromia feronia, which I believe inhabits St. Catharina— see my Journal of Travels p. 33— I want to know whether both sexes equally make the ticking noise.— I shd. think the structure at base of wings wd. be worth your investigation.—2

I received your letter of June 15th & am glad to hear the confirmation of the dimorphic case of Faramea.—3

The plants of Eschotzia from your seed (N.B. Asa Gray has been here, & says your plant & mine are both strictly E. Californica)4 have, when artificially & spontaneously self-fertilised, produced pods! but they are very small (& few in number) compared with the crossed pods.5 They are not yet ripe, so I know nothing about seed.— I shall be very curious to hear how my plants behave with you.—6

I sent your account of Begonia to Hooker, who was much struck by it.7

I have cases with Reseda odorata as capricious in respect to fertilisation as yours of Cypella(?).—8

Claparède has published what appears a splendid memoir on the Acarids; & he applies an argument like yours about the breathing organ of Crustaceans in my favour.—9

I will send in a few days a copy of a small paper on Orchids.10

In Haste pray believe me | Yours ever sincerely | Ch Darwin


The year is established by the relationship between this letter and the letter from Fritz Müller, 15 June 1869.
CD had remarked on the clicking noise of Papilio feronia (now Hamadryas feronia, the blue cracker; Peridromia feronia is a synonym) in Journal of researches, p. 38. He had inserted a note in the second edition on a drum-like structure at the base of the forewings of the insect (Journal of researches 2d ed., p. 133). For more on sound production in this species, see Yack et al. 2000. Müller had received a copy of the second edition of Journal of researches from CD in 1866 (see Correspondence vol. 14, letter from Fritz Müller, 13 February 1866).
See letter to Fritz Müller, 14 March 1869 and n. 9, and letter from Fritz Müller, 15 June 1869.
According to Emma Darwin’s diary (DAR 242), Asa Gray had visited CD on 28 August 1869. Eschscholzia californica is the California poppy. CD had worried that the seeds he obtained from a commercial grower were of a different species of Eschscholzia (see letter to Fritz Müller, 14 March 1869 and n. 11).
See letter to Fritz Müller, 18 July [1869] and n. 6.
CD had sent seeds of Eschscholzia californica after his letter to Fritz Müller of 14 March 1869.
See letter from J. D. Hooker, 13 August 1869 and n. 13.
On Reseda odorata, see the letter to Fritz Müller, 18 July [1869] and n. 5. On Cypella, see the letter from Fritz Müller, 15 June 1869 and n. 8.
CD’s annotated copy of Edouard Claparède’s ‘Studien an Acariden’ (Claparède 1868) is in the Darwin Pamphlet Collection–CUL. In discussing the parasitic lifestyle of different groups of acarids, Claparède referred to Müller’s account of the breathing apparatus in different families of crabs (see Claparède 1868, pp. 535–7; see also F. Müller 1864a, pp. 24–6, and Dallas trans. 1869, pp. 35–7). Claparède argued that differences in the grasping organs of the parasitic acarids he studied demonstrated that the adaptation for a parasitic lifestyle had developed independently and thus there was no single ancestor for all parasitic forms. In modern taxonomy, Acari is now a subclass of the class Arachnida.
‘Fertilization of orchids’.


Wants observations on a Papilio to see whether ticking noise is confined to one sex.

Experiments on self-sterility.

Will send copy of his orchid paper ["Fertilisation of orchids", Collected papers 2: 138–56].

Eschscholzia when self-fertilised, produced pods.

Letter details

Letter no.
Charles Robert Darwin
Johann Friedrich Theodor (Fritz) Müller
Sent from
Source of text
British Library (Loan 10:30) (by kind permission of English Heritage)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 6881,” accessed on 30 April 2017,

Also published in The Correspondence of Charles Darwin, vol. 17