To Roland Trimen   2 January [1868]1

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

Jan. 2d

My dear Mr Trimen

What you say about the ocelli is exactly what I want, viz the greatest range of variation within the limits of the same species,—greater than in the Meadow Brown if that be possible.2 The range of difference within the same genus is of secondary interest; nevertheless if you find any good case of variation, I shd. much like to hear how far the species of the same genus differ in the ocelli. As I know from your Orchid Drawings how skilful an artist you are, perhaps it would not give you much more trouble to sketch any variable ocelli than to describe them.—3 I am very much obliged to you for so kindly assisting me, & for your two pieces of information in your note about the sexes of the Batchian Butterfly & about the Longicorn Beetle.—4

With many thanks, pray believe me | Yours very sincerely | Ch. Darwin

1
The year is established by the relationship between this letter and the letter from Roland Trimen, 31 December 1867 (Correspondence vol. 15).
2
CD had evidently requested information about ocelli on butterflies’ wings during Trimen’s visit to Down on 28 and 29 December 1867 (Correspondence vol. 15, letter to Roland Trimen, 24 December [1867]). In his letter of 31 December 1867 (ibid.), Trimen had sought to clarify the information CD requested. The meadow brown (Maniola jurtina) is a butterfly found widely in Europe and Asia Minor. CD discussed ocelli, including those of the meadow brown, in relation to sexual selection in Descent 2: 132–4.
3
CD had received drawings of orchids from Trimen in 1862 and 1863 (see Correspondence vol. 11, letter to Roland Trimen, 31 January [1863], and letter from Roland Trimen, 16 March 1863). Watercolour sketches by Trimen sent to CD in 1863 are reproduced in Correspondence vol. 11, facing p. 246. In Descent 2: 132–3, CD cited information from Trimen about the high degree of variability of ocelli in South African moths and butterflies. He included an illustration, based on a drawing by Trimen, of different specimens of the butterfly Cyllo leda (now Melanitis leda), showing gradations in the formation of ocelli. There is a photographic slide of a drawing of C. leda, after Trimen’s original, in DAR 233.2: 76.
4
In his letter of 31 December 1867 (Correspondence vol. 15), Trimen referred CD to observations of Ornithoptera croesus (Wallace's golden birdwing) made by Alfred Russel Wallace on the island of Batchian (now Bacan) in the Malay Archipelago. Wallace had found that females of the species were more numerous than males, and that males were much more brightly coloured (see also A. R. Wallace 1864). Trimen also reported information obtained from Frederick Herschel Waterhouse on coloration in the sexes of Peritrichia cinerea, a lamellicorn beetle.

Please cite as “DCP-LETT-5772,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5772