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Darwin Correspondence Project

From Roland Trimen   31 December 1867

71, Guildford Street, | Russell Square | London, W.C.

31st. December, 1867.

My dear Mr. Darwin,

In a wilderness of ocelli,1 I have stupidly forgotten the exact nature of the information which you indicated as requisite. Am I right in thinking that you wanted one or two instances of gradation in the developement of ocellated spots in the same species? or, if that cannot be found, of gradations from a simple spot to a many-ringed ocellus in closely-allied species?2

With reference to the relative abundance of the sexes, which is apparently very generally in favour of the ♂ in butterflies, I find that Wallace (Trans. Linn. Soc. XXV “On the Papilionidæ of the Malayan Region”) notes that the ♀s of Ornithoptera Crœsus (peculiar to the island of Batchian) were “more plentiful” than the ♂s.3 This is a case in which there is a very wide difference between the sexes, the ♂ being splendidly coloured with shifting green and orange on a black ground, while the ♀ is (like those of all the nearly-allied species) dull-brown with whitish markings.

Mr. Waterhouse Junr.4 has kindly given me the name of the Cape Beetle which I mentioned to you. It is Peritrichia cinerea, a small, long-legged Lamellicorn belonging to the characteristic S. African Pachycnemidæ. The ♂ is slaty-grey clothed with whitish hairs, and the ♀ rufous-brown with pale-yellowish hairs. Though the ♀ has been described as a distinct species (P. proboscidea), I found that the sexes were placed together as one species in the British Museum collection, but without the knowledge that they were sexes of the same insect.5

I have so often taken the two in copulâ that you may rely on the correctness of this observation.

I will not forget to send you any points of importance which appear to bear upon your present special subject of research, if I am fortunate enough to chance upon them.

With my respects to Mrs. Darwin, I remain | Very faithfully yours, | Roland Trimen.

C. Darwin Esqre.

CD annotations

1.1 In a … closely-allied species? 1.5] crossed blue crayon
2.1 With … markings. 2.7] ‘Lepidoptera’ added blue crayon
2.6 shifting … ground,] underl red crayon
3.1 Mr. Waterhouse … observation. 4.2] ‘Coleoptera’ added blue crayon; crossed ink
5.1 I will … them. 5.3] crossed blue crayon


Trimen refers to the wing markings of butterflies; he was working on a paper about mimicry in butterflies (see Poulton 1920, p. xxiv).
No letter from CD requesting this information has been found, but CD may have asked for it when Trimen visited Down (see letter to Roland Trimen, 24 December [1867]). In Descent 2: 133, CD cited Trimen for information on the gradation of the ocelli of the South African butterfly Cyllo leda (now Melanitis leda).
Trimen refers to Alfred Russel Wallace’s paper ‘On the phenomena of variation and geographical distribution as illustrated by the Papilionidæ of the Malayan region’ (A. R. Wallace 1864a). CD cited A. R. Wallace 1864a on the numerical predominance of females in Ornithoptera croesus in Descent 1: 310. Batchian (now Bacan) is an island in Indonesia (Columbia gazetteer of the world).
Frederick Herschel Waterhouse.
With acknowledgment to Trimen and Waterhouse, CD cited Peritrichia as a rare example of a beetle species in which one sex differed from the other in colour (Descent 1: 367–8 and n.). The family Pachycnemidae is no longer recognised; Peritrichia is now classified within the subfamily Hopliini of Scarabideae (F. Krell, Natural History Museum, personal communication).


Columbia gazetteer of the world: The Columbia gazetteer of the world. Edited by Saul B. Cohen. 3 vols. New York: Columbia University Press. 1998.

Descent: The descent of man, and selection in relation to sex. By Charles Darwin. 2 vols. London: John Murray. 1871.

Poulton, Edward Bagnall. 1920. Roland Trimen, 1840–1916. Proceedings of the Royal Society of London, Series B 91: xviii–xxvii.


On ocelli.

Sexual differences and proportion of sexes in butterflies.


[See Descent 1: 310; 2: 132.]

Letter details

Letter no.
Roland Trimen
Charles Robert Darwin
Sent from
London, Guildford St, 71
Source of text
DAR 82: A30–1
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 5744,” accessed on 12 April 2021,

Also published in The Correspondence of Charles Darwin, vol. 15