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Darwin Correspondence Project


From Edward Blyth   19 February 1867

Feby. 19th. 1867—

My Dear Sir,

I am very sorry to hear of your indisposition, which has disappointed me of the pleasure of meeting you.1 I have been much interested with the 4th. edition of your ‘Origin of Species’,2 & have just been penning a few remarks which occurred to me, which I intended to place in your hands. As it is, I send them to you; but fear that you will regard some of them as a little fanciful.

Yours very Sincerely, | E. Blyth


Memoranda for Mr. Darwin—

N.B. The paging refers to the 4th. edit. of “Origin of Species”.

About mocking (p. 506).3 Among mammalia there is one very striking instance in the case of certain Malayan Squirrels (Rhinosciurus of Gray), which wonderfully mimic the appearance of the Tupaiæ among the Insectivora, which inhabit the same region. Size, form (elongated muzzle), colour, character of fur, flattened brush, and even the pale humeral line which is characteristic of the Tupayes, but found in no other Squirrel that I know of.4 I do not, however, perceive the object in this case of mimicry—

Wallace’s instance in the bird class is an extremely remarkable one,5 but several others occur to me. The most familiar to most ornithologists will be that of certain cuckoos (Hierococcyx), the plumage of which is exceedingly Hawk-like both in its immature and adult phases. There are 5 or 6 races of them, all peculiar to the Indian region;6 but though they approximate certain Sparrow-hawks in appearance, the most striking resemblance is with sundry southern hemisphere species allied to Pernis, but which are more widely distributed, as Cymindis uncinatus and C. magnirostris in S. America, Baza cuculoides in S. Africa and B. Reinwardtii and other species in the Malay countries, Celebes, and Australia; to the former of which they can bear no especial reference.7 Even our common cuckoo has somewhat of a hawk-like aspect

A very remarkable instance of apparent mimicry occurs in certain other true cuckoos (Surniculus Dicruroides and S. lugubris), which bear an extraordinary resemblance to the Drongos or ‘King Crows’ (Dicrurus), both in immature and adult plumage;8 & probably they lay their eggs in the Drongos’ nests, but this has not been ascertained.

Certain Doves, as several of the Macropygiæ, are also remarkably cuculine in appearance, but with what object is not very manifest. Also, some of the Graucalus and Campephaga series are very Cuculus-like.9

The Haliaëtus blagrus, which feeds chiefly on sea snakes, is remarkably gull-like, as I have thought when seeing it skim over the waves—pure white with ashy mantle; but Gulls are rare in the Indian Ocean, where indeed there are no species of large size. The great H. pelagicus also strikingly reminds one of the large black-backed Gull.10 There is a striking similarity in the barking voice of the larger Gulls and most of the Sea eagles.

The marked resemblance in facial expression of the Orang-utan to the human Malay of its native region, as that of the Gorilla to the Negro, is most striking, & what does this mean? Unless a divergence of the anthropoid type prior to the specialization of the human peculiarities, which however would imply a parallel series of at least two primary lines of human descent which seems hardly probable; & moreover we must bear in mind the singular facial resemblance of the Lagothrix Humboldtii (a platyrrhine form) to the negro, wherein the resemblance can hardly be other than accidental.11 The accompanying diagram will illustrate what I suggest (rather than maintain); & about Hylobates or Gibbons, I am not sure that I place it right, for, upon the whole, the Gibbons approximate Chimpanzee more than they do the Orang-utan, notwithstanding geographical position. Aryan I believe to be improved Turánian or Mongol12


To appreciate the likeness of a Malay to an Orangutan, you should see an old Malay women chewing pâu, & note the mobility of the lips, in additional to the general expression. However to be explained, the likeness is much less decided in other races of the grand Turánian stock. We cannot call this a case of mimicry.

I find that the leaf-nosed bats of America are emphatically platyrhine while those of the Old World are catarrhine, & the pteropodine bats are strepsirhine, like the Lemuridæ.13 The genus Taphozous bears a corresponding resemblance to Galæopithicus.14 The facial expression (or physiognomy) of the larger species of Hipposideros recals to mind that of the Orang-utan; and the ordinary bats with simple stomach and cheek-pouches remind us of the Baboon & Macacus series.15 Can we soundly interpret these resemblances, which in the cases first mentioned correspond with geographical distribution? Is there not a significant analogy between the prominent cheek-callosities of the adult male Orang-utan and the facial membranes of the horse-shoe bats?16 I would hardly like to suggest all this in print but it may be thought over.

If different genera of Cheiroptera adumbrate corresponding genera of Quadrumana, so also it may be thought that some genera of Insectivora forecast some of Carnivora; as Tupaia-Herpestes; Potamagale-Lutra; just plausibly indicating different lines of ascent from the lower order to the higher.17 May not the Bruta (i.e. Edentata and Cetacea) descend more directly from Monotremata and other placental mammalia from Marsupialia?

About parasitic cuckoos (p. 259).18 The American Coccyzi are in the condition of the Screech-owls, in having eggs and young of different ages in the same nest.19 Very closely allied to them are the Old World crested cuckoos (Coccystes), which are parasitic, and lay their eggs in the nests of birds about their own size or larger, as C. glandarius in those of magpies and crows.20 Eudynamis orientalis constantly in those of Crows, and the eggs are very similarly marked to those of the Corvi; while those of Coccystes jacobinus are greenish-blue, and are deposited in the nests of the Malacocerci which also produce blue eggs, coloured like those of Accentor modularis. Note well that parasitic Eudynamis is not migratory; and that the eggs of the parasitic Coccystes, as of Coccyzus, are of fair proportionate size; as are also those of the parasitic Molothrus!21 I suspect that Gould is right about the newly hatched cuckoo starving its companions, & so causing their carcases to be removed by the proprietors of the nest. Still it seems wrong to reject the personal observations of Jenner, as you seem to admit in p 291.22

About the origin of dogs (p. 19), consult J. K. Lords work on the Nat. Hist. of British Columbia, for very interesting observations on the derivation of the aboriginal dog of that region from the Canis latrans (which he considers as identical with the Mexican coyote, though Gray separates them. Both are thorough forms of Jackal).23 In Ld Milton & Dr. Cheadles “Journey across North America” are some remarks on the similarity of the sleigh dogs to wolves; & see also Paget’s Travels in Hungary & Transylvania.24

If the different-sized races of European or humpless cattle derive from different wild races, as primigenius, frontosus, longifrons, & trachoceros, we should suspect the same of the still more contrasted races of domestic humped cattle, which also probably descend from more than one wild original. N.B. “Bráhmini cattle” is a misnomer. Any bull dedicated to Bráhma becomes a “Bráhmini bull”, and the latter are generally of the smaller races so far as I have seen. I think it probable that there have been different wild races of the Zebu form, as likewise of the humpless taurines?25

P. 281. A nuthatch does not hammer downwards at an object, like a titmouse, or a nutcracker (Nucifraga), but delivers the blow forward with a swing of the body, if I mistake not; so different an action that one is not likely to pass into the other. I can hardly imagine a titmouse striking in the manner of a nuthatch!26

P. 417. Recent observations have shewn that there is a much greater community of species than was supposed on the two sides of the Isthmus of Panamá; on which subject consult Günther.27 The absence of corals on the western side is believed to be due to the existence of a cold current, as of course you know.

p. 556. Those curious South American birds, the Palamedea and Chauna, are most closely allied to the spur-winged geese of Africa (Plectropterus), and in reality, are true Anatidæ, though not web-footed; in the semi-palmate geese of Australia (anseranas melanoleuca), there is a decided approach in the shape of the bill to the screamers; and I cannot think how any naturalist can look at a living Palamedea without perceiving at once that it is non-palmate goose!28 A. Newton29 agrees with me in this opinion. The Parra group is quite distinct, & its affinity is with the snipe and plover series, & not at all with the Rallidæ, Anatomy, plumage, eggs, chicks, &c &c.30

P. 13 Have you ever examined the additional toe so constant in the Dorking fowls, as also in the Chinese Shang-hai bird?31 How many phalanges has it? A sixth finger or toe is exceedingly apt to be transmitted by generation in human beings, but being taken off soon after birth, & the fact kept secret, we do not generally hear of it; though I have heard of some remarkable instances, wherein almost every child of a large family has inherited this redundancy.32

For the highly predatory and carnivorous habits of the Weka Rail of New Zealand (Ocydromus australis), vide ‘Ibis’, 1862, p. 103.33 Some of the New Zealand birds seem hardly to have yet acquired sufficient distrust of man (ibid. p. 105–6), as Petroica alighting on the hand, and Carpophaga allowing to have a snare be placed on its neck; the latter ascribed to “stupidity”, whereas I should rather say non-experience. The extraordinary familiarity of the Canada jay (Perisoreus canadensis) is worthy of notice. Vide Lord and others.—34 Note diving habits of common Cape Petrel (Daption capensis ibid p. 99).35

CD annotations

1.1 Memoranda … eagles. 7.6] ‘Mimicry in Mammals & Birds’ blue crayon; ‘E. Blyth | Feby 1867’
8.1 The marked … mimicry. 9.4] ‘Man | E. Blyth | Feb 21/67’
12.1 About parasitic … p 291. 12.14 ] ‘Cuckoos | Instinct. laying eggs in other nests (very good) | Feb. 22/67/’
15.1 P. 281 … 99). 19.8] ‘Abnormal Habits in Birds for Transitions.36 | E. Blyth | Feb. 22/1867’

CD note:37

I wd have sent you Origin, if I sd have thought you wd have cared for it. | Dom. A. | I did not know about Orang & Malay but I have [del illeg] to consider Vogts view, founded on Gratiolets remark on brain. | (Mimicry) (Bats) (Cuckoos most valuable remarks) Dogs I have used the [inf] | I regretted since I did not see in Lond, but during both last days was confined to house. | Sexual Selection.— too many questions to ask | Title of paper. I find [del] I more in your paper, even when you are not writing on subject.— Even in last L. W. summer plumage of gulls & plover nuptial | Spur-winged sexual


See letter to Edward Blyth, [19 February 1867].
The fourth edition of Origin was published in November 1866 (Publishers’ Circular).
CD made a number of additions to his section on mimicry or ‘Analogical resemblances’ in Origin 4th ed., pp. 502–6; see also Peckham ed. 1959, pp. 663–70.
John Edward Gray listed ‘Rhinosciurus Tupaioides’, the sharp-nosed squirrel, in J. E. Gray 1843, p. 195; it is now known as Rhinosciurus laticaudatus, the long-nosed squirrel (Nowak 1999, p. 1288). Nowak 1999, pp. 244–9, classifies the taxonomically controversial Tupaia and Tupaiidae (tree shrews) as the only genus and family in the order Scandentia. Though CD did not add Blyth’s information to later editions of Origin, when discussing the mimicry most common in insects (see n. 5, below), he changed his comment that no cases of mimicry were known in ‘larger animals’ to read ‘larger quadrupeds’ (Peckham ed. 1959, p. 669).
In Origin 4th ed., p. 506, CD wrote that the known cases of mimicry were all in insects except for Alfred Russel Wallace’s one case of mimicry in birds. Though CD included no details, Blyth evidently knew of Wallace’s case of an oriole (Mimeta bouruensis) mimicking a honeysucker (Tropidorhyncus bouruensis) on the Island of Bouru (or Buru); see A. R. Wallace 1863, pp. 26–8.
Blyth refers to the hawk-cuckoos. Birds of the world 4: 548–50 lists six species of hawk-cuckoos in the genus Cuculus; the genus is still called Hierococcyx by some sources. For Blyth on the classification of the family Cuculidae, see Blyth 1842–3.
Blyth refers to the honey-buzzards (Pernis). When Blyth mentions ‘Cymendis uncinatus and C. magnirostris’, he is referring probably to the hook-billed kite (Chondrohierax uncinatus), and possibly to the roadside hawk (Buteo magnirostris), both of South and Central America; see Peters et al. 1931–87, 1: 285–6, 361–2. Baza cuculoides, the African cuckoo-hawk, is now named Avecida cuculoides, and the Pacific baza now includes a subspecies named A. subcristata reinwardtii (Birds of the world).
Two species of Surniculus in the family Cuculidae are called drongo-cuckoos; S. dicruroides is now S. lugubris dicruroides (Birds of the world 4: 569). However, see also Davies 2000, p. 266. Dicrurus is a genus in the drongo family, Dicruridae.
Macropygia is a genus of cuckoo-doves in the family Columbidae (pigeons and doves); see Birds of the world 4: 143–6. The family Campephagidae, or cuckoo-shrikes, includes Coracina, Campephaga, and under some classifications, Graucalus.
Blyth refers first to what is now called Haliaeetus leucogaster, the white-bellied sea-eagle (see Birds of the World 1: 121–3). He also refers to H. pelagicus, Steller’s sea-eagle, and to Larus marinus, the great black-backed gull. Blyth had been curator of the Museum of the Asiatic Society of Bengal, Calcutta, India from 1841 to 1862 (DNB). For more on Blyth’s career, see Eisely 1979 and Brandon-Jones 1995.
There are now two recognised species of Lagothrix (woolly monkeys), both found in South America; L. lagotricha and L. flavicauda (Nowak 1999, pp. 538–40). The Platyrrhini are the New World monkeys, but Blyth is probably using ‘platyrrhine’ to mean flat-nosed. For CD’s recent discussions on the origin of human races, see Correspondence vols. 12 and 13. For discussion of nineteenth-century western perspectives on the human races, see, for example, Stocking 1982, S. J. Gould 1997, and Graves 2002, pp. 37–73.
Chimpanzees are found in Africa and gibbons in south-east Asia; orang-utans are now limited to Sumatra and Borneo. For discussions of other mid-nineteenth-century classifications of primates, including humans, see Stanton 1960 and S. J. Gould 1997. On modern classifications of primates, see Nowak 1999, pp. 490–3. The term Turanian is now applied to any of the peoples speaking Ural-Altaic languages, but in the mid-1860s the term was usually applied to people who spoke any of the Asian languages, and were generally nomadic rather than agricultural (see OED, and Stocking 1987, pp. 58–9). For a contemporary source on the development of languages and human races, see C. Lyell 1863, pp. 454–70. CD did not include a genealogical chart of human descent in Descent, but see Descent 1: 185–213, 2: 385–96 for his conclusions.
Blyth refers first to the American leaf-nosed bats (Phyllostomidae; Nowak 1999, pp. 350–3). For the Old World leaf-nosed bats, see n. 15, below. Blyth is also probably referring to the Family Pteropodidae, the Old World fruit bats. The terms platyrrhine, catarrhine, and strepsirrhine are usually used to refer to primates. Platyrrhine: flat-nosed, widely spaced nostrils facing outwards (New World monkeys); catarrhine: nostrils close together, oblique, and directed downwards (Old World apes and monkeys) (OED). Some classifications include the Strepsirrhinae. Strepsirrhine: having a moist rhinarium and a cleft upper lip bound to the gum (e.g., lorises and lemurs; Allaby ed. 1999). See also Fleagle 1999, pp. 82–4, 136–7.
Blyth refers to Taphozous, tomb bats in the family Emballonuridae (Nowak 1999, pp. 307–9), and to Galeopithecus, flying lemurs and colugos (now called Cynocephalus in the order Dermoptera); see ibid., pp. 250–2.
Hipposideros is the genus of Old World leaf-nosed bats (Nowak 1999, pp. 333–7). Blyth also refers to the macaques (Macaca).
Horseshoe bats (Rhinolophidae) have a ‘nose-leaf expansion of the skin surrounding the nostrils’; see Nowak 1999, pp. 329–32.
Blyth refers to the bat order (Chiroptera), and to what older classifications called the order of Quadrumana (monkeys, apes, baboons, and lemurs). He also refers to the insectivore Tupaia (tree shrew), the carnivore Herpestes (mongoose), and the insectivore Potamogale (giant African water shrew or giant otter shrew), and the carnivore Lutra (Old World river otter).
In Origin 4th ed., p. 259, and in earlier editions, CD speculated on how the parasitic European cuckoo acquired its habit of laying eggs in other birds’ nests.
Blyth refers to members of the genus Coccyzus; for example, C. americanus, the yellow-billed cuckoo, often lays eggs at intervals throughout the breeding season (Birds of the world 4: 595–6).
Coccystes is a synonym of Clamator. Clamator glandarius is the great spotted cuckoo of Europe and Africa. Some Clamator species are called crested or pied cuckoos (Birds of the world 4: 547–8). See Peters et al. 1931–87, 4: 12, and Davies 2000, pp. 98–108, 263.
The common koel or Asian koel, Eudynamys scolopacea, now includes a subspecies E. s. orientalis; it is known to lay eggs in the nests of Corvus (crow) species (Birds of the world 4: 570). The pied cuckoo or Jacobin cuckoo is now called Clamator jacobinus (see n. 20, above), or Oxylophus jacobinus; in India, its eggs are bluish (Birds of the world 4: 547). They evidently resemble eggs of a babbler genus, Turdoides; Malacocircus and Malacocercus are synonyms for some Turdoides species (Peters et al. 1931–87, 10: 331). Accentor modularis is the hedge-sparrow. In Origin 4th ed., pp. 258–9, CD further emphasised his point, made in Origin, p. 217, that laying eggs at intervals would be difficult for a migratory bird since extended hatching time would require a bird to nest longer. He also discussed whether parasitic birds tended to lay eggs in nests containing eggs similar in appearance (Origin 4th ed., p. 261; see also Correspondence vol. 8, letter to W. B. Carpenter, 6 January [1860] and n. 6). CD discussed the parasitic habits of Molothrus, the cowbird, in Journal of researches 2d ed., pp. 52–4.
In Origin 4th ed., pp. 261–2, CD added a discussion of John Gould’s belief that the nestlings of the parent bird starved to death rather than being ejected from the nest by the young cuckoo (J. Gould 1873, vol. 3, text with plates LXVII and LXVIII); J. Gould 1873 was first issued in twenty-five parts from 1862 to 1873; part 4, issued by 1865, included the plates and texts on cuckoos (see Ibis n.s. 1 (1865): 98–9). Edward Jenner had observed the nestling cuckoo ejecting the eggs or young of the foster-parent (Jenner 1788, p. 225). CD did not explicitly refer to Jenner in the fourth edition of Origin; however, he included the ‘young cuckoo ejecting its foster-brothers’ as an example of ‘small consequences of one general law, … namely, multiply, vary, let the strongest live and the weakest die’ on page 291. CD did mention Jenner’s ‘celebrated paper’ in the manuscript of his ‘big book’ on species (see Natural selection, p. 508 n. 2). For recent conclusions on cuckoo nesting behaviour, see Davies 2000.
Blyth refers to The naturalist in Vancouver Island and British Columbia, in which John Keast Lord observed that the ‘true Indian dog’ was a tame coyote, but only in inland areas where there were no opportunities for breeding with imported dogs (Lord 1866, 2: 218–25). CD cited Lord 1866 in Variation 1: 22–3; both Lord and CD noted that the coyote was Canis latrans. For John Edward Gray’s classification of the genus Canis, see J. E. Gray 1843, pp. 57–9.
Blyth refers to William Wentworth Fitzwilliam (Viscount Milton), Walter Butler Cheadle, and their book, The north-west passage by land (Fitzwilliam and Cheadle [1865]). In J. Paget 1839, 2: 18, John Paget mentioned that the Hungarian shepherd-dog looked much like a wolf; see Variation 1: 24.
CD made minor changes to Origin 4th ed., p. 19, that slightly strengthened his assertion that European cattle and the Indian humped cattle ‘descended from a different aboriginal stock’; he noted facts communicated to him by Blyth (see Peckham ed. 1959, p. 92). CD also cited Blyth on Indian cattle in Origin 4th ed., p. 301 (Peckham ed. 1959, p. 434). CD did not use the term ‘Bráhmini’ of cattle in Origin or Variation. In Variation 1: 79–83, he referred to ‘Zebus’ in India, with the specific name of Bos indicus; CD cited Blyth on the humped cattle twice in these pages.
In Origin 4th ed., p. 212, CD noted that he had seen titmice hammering yew seeds to break them ‘like a nuthatch’. On page 281, he suggested that natural selection might preserve each slight variation of the titmouse’s beak, until it had one ‘as well constructed for this purpose as that of the nuthatch’.
In Origin 4th ed., p. 417, CD wrote, ‘No two marine faunas are more distinct, … than those of the eastern and western shores of South and Central America’. Blyth probably refers to Albert Charles Lewis Günther’s recent paper on fishes of the states of Central America; an account was given in Proceedings of the Zoological Society of London (1866): 600–4. See also Günther 1864–6, and Correspondence vol. 14, letter from J. D. Hooker, 14 December 1866 and n. 10. In Origin 5th ed., p. 424, CD noted Günther’s conclusion that thirty per cent of the fishes were the same on each side of the isthmus of Panama, leading naturalists to believe that the isthmus was formerly open.
In Origin 4th ed., pp. 556–7, CD wrote, ‘How strange it is … that upland geese, which never or rarely swim, should have been created with webbed feet.... But on the view of each species constantly trying to increase in number, with natural selection always ready to adapt the slowly varying descendants of each to any unoccupied or ill-occupied place in nature, these facts cease to be strange, or perhaps might even have been anticipated.’ CD’s comment led Blyth to mention other apparently related geese with webbed, semi-webbed, or non-webbed feet. Blyth refers here to the screamers, now the family Anhimidae, of South America; these include two species of Chauna, and Anhima cornuta, the latter of which is also called Palamedea cornuta (Birds of the world 1: 534–5). The screamers do not have webbed feet. Plectropterus gambensis, in the family Anatidae, is also web-footed. Anseranas melanoleuca (a semi-palmate goose) was Gould’s name for what is now called A. semipalmata, the magpie goose (Birds of the world 1: 575). All birds mentioned have hooked bills.
Alfred Newton.
The ‘Parra group’ were birds known as jacanas, many of which belonged to the genus Parra. Jacanas had formerly been placed in the family Rallidae, but by the mid-1860s, some systematists placed them in a new family, Parridae (see Blyth 1866–7, p. 170). The family Parridae has since been renamed Jacanidae, which in modern classification is often included in the order Charadriiformes with snipes (family Scolopacidae) and plovers (family Charadriidae), while the family Rallidae is in the order Gruiformes (see Birds of the world 3: 108–12, 276–7, 289–91).
In Origin 4th ed., p. 13, CD began discussing ‘inheritable deviations of structure’. CD referred several times to the fifth toe of the fowls Blyth mentions, in addition to that of some sub-breeds, in Variation, noting that it indicated a long period of selection (ibid. 1: 260, 2: 202, 238).
Blyth had earlier equated the extra toe in fowls to the supernumerary digit in dogs and the sixth finger in human beings (see Correspondence vol. 5, letter from Edward Blyth, [1–8 October 1855] and n. 8). CD collected information on polydactylism in 1863 (see Correspondence vol. 11, especially letter to T. H. Huxley, 27 June [1863]). In concluding his discussion of extra digits in humans and other animals, CD suggested the case was ‘one of reversion to an enormously remote, lowly-organised, and multidigitate progenitor’ (Variation 2: 17).
Blyth refers to an article in Ibis (J. F. J. von Haast 1862); Julius von Haast described the weka (now Gallirallus australis in the family Rallidae) as omnivorous (p. 103).
Blyth refers to the ‘Totoara, the New Zealand Robin’ (the Toutouwai, Petroica australis), and to the pigeon, ‘Carpophaga novæ zelandiæ’ that Haast described as ‘so stupid’ as to sit on a branch until caught by a snare (J. F. J. von Haast 1862, pp. 105, 106). CD discussed the acquired fear of humans in Origin 4th ed., pp. 253–4; see also Journal of researches 2d ed., pp. 398–401. For Lord’s description of the Canada jay, see Lord 1866, 2:151–2.
Blyth refers to the Cape petrel’s diving behaviour as described in Layard 1862; the scientific name is now Daption capense. For CD’s comments on another diving petrel, see Origin 4th ed., p. 213.
A section entitled ‘On the origin and transitions of organic beings with peculiar habits and structure’ in Origin 4th ed., pp. 207–18, mentioned several of the birds and mammals Blyth discusses here; however, CD did not add the enclosed information on the habits or structures to later editions.
Most of the content of CD’s note is a reminder for his letter to Blyth of 23 February [1867]. CD refers to Carl Vogt and Louis Pierre Gratiolet.


Encloses memorandum on Origin [1866]

discussing mimicry in mammals and birds,

abnormal habits shown by birds,

behaviour of cuckoos,

and analogies existing between mammals of the same geographical region.

Speculates on possible lines of development linking groups of mammals.

[CD’s notes on the verso of the letter are for his reply.]

Letter details

Letter no.
Blyth, Edward
Darwin, C. R.
Sent from
Source of text
DAR 160: 209, 209/1 & 2, DAR 47: 190, 190a, DAR 80: B99–99a, DAR 205.11: 138, DAR 48: A75
Physical description
1p †, encl 5pp †

Please cite as

Darwin Correspondence Project, “Letter no. 5405,” accessed on 29 July 2016,