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Darwin Correspondence Project

To C. F. Claus   28 January 1869

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

Jan 28 1869

Dear & esteemed Sir

Your letter has given me great pleasure, for permit me to say that I have long honoured your name as that of one of the best naturalists in Europe. I am very much obliged for your two Memoirs, which I am sure will interest me, but I am a poor German scholar & I have another book which I must finish reading first.1

I earnestly hope that you will publish your lecture, as the judgment of so experienced a naturalist must be of value to every one; & for myself I much wish to read your criticisms & facts. Of course I think very highly of Häckel’s abilities & his works; I should indeed be very insensible to praise if I did not do so; but I dare say he is too enthusiastic & too bold in drawing conclusions.2 I have been particularly glad to hear what you say about M. Wagner’s interesting pamphlet. Perhaps I have underrated the importance of isolation, but I am now correcting a new edit. of my “Origin of species”, & I do not find that I have much or any thing to alter on this head.3

I cannot tell you how glad I am to hear that you intend to study the metamorphoses of the Lepads.4 As you are a much better dissector than I am, & have so much knowledge of the lower Crustaceans, I have no doubt that you will find much that I have overlooked or misunderstood.

I still cannot avoid believing that the lateral horns of the larvæ in the first stage include the antennæ of the second stage.5 I wish you could be induced to examine the curious organ which I suppose I falsely called the acoustic sack.6 But beyond every thing I hope that you will be able to examine the Complementary males of Scalpellum, which no one else has ever seen.7 I shall never forget my astonishment when I first made out their nature. I shd think you wd be able to find some where specimens in spirits. I grieve to say I can give you very little help. When I finished my work I returned almost all the specimens to their owners. The few which I kept have been entirely forgotten, & now I find to my great disappointment that some which wd have been useful to you are quite dried up. I have however the following specimens not quite spoilt.

(1) Xenobalanus, that curious form resembling Lepas but really allied to Coronula—in pretty good state8

(2) A single small Scalpellum; & I am nearly sure that with only a hand-lens, I see a complementary male on each side, but I do not like to cut off the valve to examine carefully.

(3) The shell of Concholepas, after being treated with acid, & which formerly abounded with Cryptophialus but whether they are in a good state I will not say.9

(4) Some fragments of shell with Alcippe,10 but again I do not know in what state.—

Lastly 17 slides with various fragments & minute specimens; I can see one male Alcippe in a pretty good state, & some larvæ of the first stage of Scalpellum; these larvæ are of remarkable size.—

Now wd these specimens be worth your acceptance? They need not be returned, & I can send a list of the slides, which however are in a poor condition. If you think these specimens worth sending you must tell me the best means of sending them. They will all go in a very small box, but much too heavy for the post.

Lastly you must let me have the pleasure of sending you in 2 or 3 months time the New edit. of the Origin some parts of which I hope I have improved.11

With the most sincere esteem & respect, I remain Dear Sir Yours very faithfully | Ch. Darwin

P.S. Would you have the great kindness to send me your Photograph, as I have a collection of the best naturalists.—


See letter from C. F. Claus, 24 January 1869 and nn. 2 and 6. CD refers to Claus 1868a and 1868b.
For Claus’s criticism of Ernst Haeckel, see letter from C. F. Claus, 24 January 1869 and n. 5.
See letter from C. F. Claus, 24 January 1869 and n. 4. CD began working on the fifth edition of Origin in December 1868 (Correspondence vol. 16, Appendix II). For CD’s response to Moritz Wagner, see Origin 5th ed., p. 120.
In his letter of 24 January 1869, Claus informed CD that he was working on the metamorphosis of pedunculated barnacles (family Lepadidae) and included a paper on the subject (Claus 1868b).
For CD’s understanding of the homologies of the appendages in cirripedes, see Correspondence vol. 15, letter to Anton Dohrn, 26 November [1867] and n. 5.
For CD’s interpretation of the ‘curious organ’ as an auditory sac and subsequent criticism of his view, see Correspondence vol. 13, letter to Fritz Müller, 10 August [1865] and n. 8.
See letter from C. F. Claus, 24 January 1869 and n. 9. For the criticism of CD’s discovery of ‘complemental’ males, see Correspondence vol. 13, letter to Fritz Müller, 10 August [1865] and n. 9.
Xenobalanus and Coronula are genera of sessile barnacles in the family Coronulidae (whale barnacles). See Living Cirripedia (1854), p. 651 and plate 17. In Xenobalanus, the body is everted into a stalked structure that superficially resembles the peduncle of Lepas (for more on the attachment structures and morphology of whale barnacles, see Seilacher 2005).
Concholepas is a gastropod genus (family Muricidae). Cryptophialus is a genus of burrowing barnacles, first discovered by CD on the Beagle voyage; this genus inspired CD’s later work on Cirripedia (see Living Cirripedia (1851), p. v; see also Autobiography, p. 117).
The genus Alcippe is now Trypetesa.
The fifth edition of Origin was published in May 1869 (Publishers’ Circular, 1 July 1869, p. 386).


Autobiography: The autobiography of Charles Darwin 1809–1882. With original omissions restored. Edited with appendix and notes by Nora Barlow. London: Collins. 1958.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Living Cirripedia (1851): A monograph of the sub-class Cirripedia, with figures of all the species. The Lepadidæ; or, pedunculated cirripedes. By Charles Darwin. London: Ray Society. 1851.

Living Cirripedia (1854): A monograph of the sub-class Cirripedia, with figures of all the species. The Balanidæ (or sessile cirripedes); the Verrucidæ, etc. By Charles Darwin. London: Ray Society. 1854.

Origin 5th ed.: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 5th edition, with additions and corrections. By Charles Darwin. London: John Murray. 1869.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Seilacher, Adolf. 2005. Whale barnacles: exaptational access to a forbidden paradise. Paleobiology 31 (2): 27–35.


Thanks CC for two memoirs [see 6575. The other was possibly "Die Cypris-ähnliche Larve der Cirripedien", Schr. Ges. Beförd Naturw. Marburg (1869)].

Haeckel is too enthusiastic and too bold in drawing conclusions.

CD sees no reason to add to what he says on isolation, in new edition of Origin.

Lists specimens he has available for CC’s intended study of metamorphoses of Lepas.

Please cite as

Darwin Correspondence Project, “Letter no. 6581,” accessed on 1 October 2023,

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