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Letter 1645

Darwin, C. R. to Huxley, T. H.

8 Mar [1855]

    Summary Add

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    Thanks THH for corroborating his observations. Discusses metamorphosis of ovaria to cement organs. Ovaries, germinal vesicles, and anatomy of cirripedes. Difficulties of classification, and observation.

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    THH's article on Mollusca [Charles Knight, ed., English cyclopædia: a new dictionary of universal knowledge (1854–70) 3: 855–74].

Transcription

Down Farnborough Kent

March 8th

My dear Huxley.

I really am much obliged to you for looking at my preparations; I feel it quite a comfort that some one shd have seen what once filled me with astonishment.— You cd not do better than take Conchoderma aurita for the cement-glands, (if you ever have time to look for yourself) for everything here is in its very simplest stage: & here you will be able with care to see what I consider the strangest part of the whole structure of cirripedes the metamorphosis or adaptation of part of the branching ovaria to the cement-organs, about the truth of which, strange as it may be, I cannot doubt.— In my volume on the Lepadidæ p. 57 & 58, you will see why I consider the salivary glands of Cuvier to be the true ovaria. It was difficult to doubt the meaning of the passage of the little pellets of cells with nuclei from the glands down the two unbranched ovarian tubes into the mass at the base of shell or into the peduncle. The ova are never developed in these glands. Conchoderma aurita is eminently good for tracing development of ova, (before impregnation) from the tubes round the base, of the sack, (within the capitulum) lie in a single plane.

I felt to a degree you will hardly appreciate, the want of knowledge of minute or microscopical structure: if I had to begin again, I wd devote 6 months to understand cells, nuclei, germinal vesicles &c &c. My idea, (I know not how unlikely) is that the germinal vesicles alone are formed in the true ovaria (by the mouth) & that the whole rest of development before impregnation goes on at basis or within peduncle, & impregnation takes place within the sack, after the exuviation, by which the eggs may be said to be laid.—

Lastly the main reason which caused me to separate the Cirripedes so completely as I have from ordinary Crustaceans, is, my firm belief, that the resemblance of the larvæ to Entomostraca is only analogical & that the natatory organs are not at all similar in the two,—that the law of development is very different. I give this conclusion briefly at p. 16 of the Balanidæ, & my reasons at tedious length at p. 102.—

How difficult a subject is the classification of the higher groups in any class: see how Dana & Milne Edwards, such competent judges, differ! Dana approves of my classification, but will not, from analogy alone, admit my views of the homologies of the limbs.—

Should you ever go on with subject, do read my account of Proteolepas: it strikes me as a truly extraordinary animal.—

I promise I will never bore you again on Cirripedes.—

I must just say, that you are quite right to doubt me in every way, for what blunders are made. I stopped being sent to Royal Socy an elaborate paper, in which a quite independent parasite was minutely described, as the ovarium of a Balanus, & all the stages of development of the eggs of the parasite were minutely described as those of Cirripedes!—

Many thanks for your paper out of the Encyclop: on Mollusca, of which I had heard from two quarters. I have read it with attention & interest, for I had often wondered how a gasteropod, a bivalve, & cephalopod cd be brought to same type. It appears to me satisfactory, but it wd be hypocritical in me to let you suppose my opinion of any value, for really I do not know enough of the essential points of structure to form an independent opinion.—

An acephalous Mollusc has always looked to me a complete mystery, & I really know no more about it, than a man does, who has only eat oyster patties; the relation of the animal to the shell & crust being about the same in my eyes.— There was no reason for your writing down to ignoramuses, & indeed without beautiful figures, I shd think you could not; but if you ever lectured on the subject, I think you ought to take more pains in making your hearers realise the structure of the acephalous mollusca, & heteropods, & indeed cephalopods, & how a common land-snail corresponds with a whelk.— I can, however, so far judge that to anyone commencing to examine for himself the several great classes of Mollusca, your paper would be quite invaluable.—

Pray believe me | Your's very sincerely | C. Darwin

    Footnotes Add

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    f1 1645.f1
    See letter to T. H. Huxley, 20 February [1855]. CD had asked Huxley to examine specimens of cirripedes in order to give his opinion on CD's interpretation of the structure of the cement glands and the female reproductive system.
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    f2 1645.f2
    See Correspondence vol. 4, Appendix II.
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    f3 1645.f3
    In Living Cirripedia (1851): 57–8, CD stated that he had traced in two genera of pedunculated cirripedes the ovarian ducts from the foot of the peduncle to the ‘two glandular masses’ thought by Georges Cuvier, owing to their position near the stomach, to be the salivary glands. Within these glands, CD discerned cellular masses resembling ‘ovigerms with their germinal vesicles and spots’. ‘Hence’, he wrote, ‘I conclude, that these two gut-formed masses are the true ovaria.’ (ibid., p. 58).
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    f4 1645.f4
    For CD's use of embryological criteria for classification, see Correspondence vol. 4, Appendix II.
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    f5 1645.f5
    CD discussed this difference of opinion in Living Cirripedia (1854): 17. Whereas James Dwight Dana, like CD, regarded the cirripedes as different enough from other Crustacea to form a distinct sub-class (Dana 1852–3, pt 2, p. 1407), Henri Milne-Edwards placed them as a sub-group of the higher Crustacea, the Entomostraca (Milne-Edwards 1852, p. 119).
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    f6 1645.f6
    CD described the unusual homologies of the body of Proteolepas bivincta in Living Cirripedia (1854): 594–6. Owing largely to the differences in the development of this form from other cirripedes, CD classified Proteolepas as the sole species in its order.
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    f7 1645.f7
    The paper has not been identified.
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    f8 1645.f8
    T. H. Huxley 1855a, in which Huxley proposed an archetype for the Mollusca. See letter to T. H. Huxley, 20 February [1855].
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