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Letter 5785

Trimen, Roland to Darwin, C. R.

13 Jan 1868

    Summary Add

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    Variations in the ocelli of Lepidoptera.

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    Encloses six pages from his catalogue of S. African butterflies [Rhopalocera Africae australis, 2 pts (1862, 1866)].

Transcription

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

13th. January, 1868.

My dear Mr. Darwin,

I have the pleasure of enclosing a sketch of the best case of variation in ocelli that I have been able to discover among the Lepidoptera.

The drawings have been carefully made, by measurement, from specimens in my own collection, and you may rely upon their being tolerably exact.

Cyllo Leda is a butterfly so extremely subject to variation in the form, colouring, and marking of the wings, that I thought it not unlikely that the long series in the British Museum might contain examples exhibiting a still wider difference in the ocelli than could be found among my own specimens; but, since the Museum has been re-opened, I have looked through the series without finding any more striking instances than those which I have figured.

I forward an old proof of that portion of Part 2 of my Catalogue of S. African Butterflies which refers to C. Leda, in order to give you some idea of the colouring, as well as of the wide geographical range of the species.

The tendency of this butterfly to vary is not only very strong, but seems to work at random, as it were. The differences in outline of the forewing distinguish neither the sexes, nor specimens from different localities; and the same may be said of the varying colours and markings. I have ♂ examples from the very same spot (a wood edging the Botanic Gardens at Port Natal) ranging from the straight hindmargin & faint, dingy colouring of Fig. A, to as falcate a form, and as rich decided hues, as those shown by the ♀ figured (AI).

Specimens which have the ocelli very large & strongly-marked on the upperside are often found with the underside ocelli minute and faintly defined (e.g. Fig. A.I, which has the ocelli of the inferior surface not much larger than those of Fig. CI); and vice versa (e.g. Fig. C, which is almost like Fig. A on the upperside, and has only one ocellus in the hindwing.)

It is rare to find the 3rd. (lowest) ocellus in the forewing of the ♀, shown in Fig. AI, the two confluent ocelli being the rule, though a few specimens exhibit rudimentary traces of a third.

The proof I send will, I think, sufficiently inform you as to the wonderful variation in the colouring of the underside; but, even on the upperside, the variation is considerable, the fulvous ranging from the very indistinct bar inwardly bordering the ocelli in Fig. A, to the clear rich colouring surrounding the ocelli in Fig. AI., which also more or less suffuses all the upper surface.

The family (Satyridæ) to which the butterfly belongs, is one in which nearly all the genera consist of ocellated species; and I think I shall be supported by lepidopterists in the statement that there is no character of mere marking or coloration so unstable as the ocelli, both in number and size. The species of Mycalesis are particularly noticeable for variation in this respect.

I have not as yet found any good case of progressive variation in the ocelli in any genus, though I am under the impression that such exist.

The most distinguished family for ocelli among the Moths is the Saturniidæ, of which our English ``Emperor Moth'' is a familiar example. One large South African species, Gynanisa Isis, has the hindwing ocellus occupying nearly the whole of the central portion of the wing, & consisting of 9 distinct rings, viz: black (large centre, with semi-transparent crescent), 1 ochre-yellow, 2 black, 3 ochre-yellow, 4 pink, 5 white, 6 pink, 7 brown, & 8 whitish. The ocellus of forewing in this species is small, & consists of but 3 rings (incomplete) viz: black, pink & white. In most of the S. African Saturniidæ the ocellus of forewing is much smaller than that of hindwing, & often represented only by an irregularly-shaped transparent mark; but in Saturnia Apollonia the reverse is the case, the ocellus of the anterior wing being considerably larger than that of the posterior. But I have not found much variation within the limits of a species among the Saturniidæ.

Believe me, with sincere regard, | Very faithfully yours | Roland Trimen



[Enclosure: 1]

DIAG HERE

    Footnotes Add

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    f1 5785.f1
    See letter to Roland Trimen, 2 January [1868] and n. 2.
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    f2 5785.f2
    The references are to Cyllo leda (now Melanitis leda), and to R. Trimen 1862--6, pp. 186--9. The proof-sheets are in DAR 84.1: 43--5; several passages are scored in pencil, and in blue and red crayon, probably by CD.
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    f3 5785.f3
    Trimen refers to the Durban botanic garden in Natal, South Africa. On the history of the garden, see McCracken 1997, pp. 42--3. Port Natal was renamed Durban in 1835 (Columbia gazetteer of the world).
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    f4 5785.f4
    Figure A, showing the fore-wing of a male specimen, has been cut from the enclosure; the drawing, together with figures A1, B, and B1, are reproduced in Descent 2: 133.
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    f5 5785.f5
    Figures C and C1 were not reproduced in Descent.
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    f6 5785.f6
    CD quoted this sentence, with slight modifications, in Descent 2: 132: `Mr. Trimen writes to me, ``no characters of mere marking or coloration are so unstable in the Lepidoptera as the ocelli, both in number and size''.'
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    f7 5785.f7
    Mycalesis is the genus of bushbrown butterflies.
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    f8 5785.f8
    Trimen refers to Saturnia pavonia.
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    f9 5785.f9
    Gynanisa isis is now G. maja. Trimen's description of the moth is given in Descent 2: 132.
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    f10 5785.f10
    Saturnia apollonia has not been identified; however, the description matches that of the African silkmoth Heniocha apollonia (Ian Kitching, Natural History Museum, personal communication).
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    f11 5785.f11
    The meadow brown butterfly is now Maniola jurtina (family Nymphalidae). In Descent 2: 132--3, CD reported that Alfred Russel Wallace had shown him a series of meadow brown specimens with gradations in ocelli. In a note dated 21 June 1867 (DAR 84.1: 46), CD wrote: `Wallace in remarking on Peacock's tail says that in the meadow brown butterflies there are infinite variations from a minute black spot to an eye elegantly shaded. This is a far better illustration than mine of pigeon wing-bars.'
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    f12 5785.f12
    CD also discussed the variability of ocelli on the plumage of birds in Descent 2: 133--4.
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    f13 5785.f13
    Oreina ligea is now Erebia ligea, the Arran brown butterfly. This information was given in the letter from Roland Trimen, 26 March 1868.
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    f14 5785.f14
    CD probably refers to notes on sexual differences in butterflies that he later received in the letter from George Fraser, 12 April 1871 (Calendar no. 7677). Fraser's notes were subsequently published in Nature, April 1871, p. 489; CD cited this article in Descent 2d ed., 2: 312.
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    f15 5785.f15
    RT. delt.: R. T. delineavit, i.e. R. T. drew it (Latin).
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