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Letter 2425

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

8 Mar [1859]

    Summary Add

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    Sends THH questions about "serial homologies" and "vegetative repetition" in Mollusca and Radiata.

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    Abstract volume [Origin] nearly completed.

Transcription

Down Bromley Kent

March 8th

My dear Huxley

When I feel myself chasing wild geese & get beyond my limited tether of knowledge, you always rise before me, as an awful bugbear, ready to pitch into me; & thus you do me great good service unintentionally. Now I have been thus thinking of you this morning & will you be so kind as to read over the enclosed queries & doubtful remarks—that is if you can understand at what I am driving, which is very doubtful.

Further if you can answer me briefly I shd be much obliged; but if that be not possible, as is very probable, as the answer may require guarding & explaining, I beg you not to answer, but just say so; for I could leave out the two or three sentences, which I shd like to put in, or defer the subject till we meet, & I could hear how the truth lies vivâ voce.—

I am working myself half to death to get my Abstract volume completed (which thank God it nearly is) & I sincerely hope that you are in different case from | Yours most truly | C. Darwin

[Enclosure]

(1) My impression is that in the whole Molluscan Kingdom we have not many (or any) clear cases of “serial homologies” in the same individual; like the skull in Vertebrata in relation to the vertebræ, or like jaws & segments of head in relation to legs & segments of body in the Articulata.

(2) My impression is that no mollusca, not even the lowest, offer good instances of a “vegetative repetition” (to use Owen's ugly phrase) of parts of importance. The arms of Cephalopods seem (in my ignorance) chief exception, & we get some poor serial homologies in the arms of certain Cephalopods. I hypothetically wish to connect no 2. as cause of no 1.—

(1) In single plant (ie in flower or leaf-bud) we often have many, almost indefinitely many, whorls of the same homological part; & in each separate whorl almost an indefinite number of such parts.— How far does this hold true with the Radiata, in the largest sense? In Encrinite can the stem be looked at as a pile of simple whorls; or is it not rather an elongated & modified footstalk of the single main whorl? In Radiata is not the number of important parts in each (the single?) whorl generally or always few & definite. Do the numerous tentacula in certain Actineæ or rays in certain Asteriases make a real exception; I fancy these tentacula (& rays) are only a vegetative repetition of an un important part, & not comparable to the repetition of stamens, pistils & petals of plants.—

I imagine that there are not good cases of “serial homologies” in individual species of the Radiata.— And this seems to be an odd contrast with plants.—

    Footnotes Add

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    f1 2425.f1
    Dated by CD's reference to having nearly completed the composition of his ‘abstract’ (‘Journal’; Appendix II).
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    f2 2425.f2
    CD was writing chapter 13 of his ‘abstract’, on classification, morphology, and the mutual affinities of organic beings (Origin, pp. 411–58). He recorded having finished it on 19 March 1859 (‘Journal’; Appendix II).
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    f3 2425.f3
    The enclosure was extensively annotated by Huxley, presumably to assist him in responding to CD's queries. See letter from T. H. Huxley, [9–12 March 1859].
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    f4 2425.f4
    Richard Owen discussed the ‘law of vegetative or irrelative repetition’ in R. Owen 1855, pp. 641–3, to account for what he called the ‘multiplication of organs performing the same function’. CD's annotated copy of this work is in the Darwin Library–CUL. The index he prepared for it includes the note: ‘643–vegetative repetition’. The phrase actually appears on p. 641.
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    f5 2425.f5
    See letter from T. H. Huxley, [9–12 March 1859].
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    f6 2425.f6
    See letter from T. H. Huxley, [9–12 March 1859].
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