On THH's paper on cephalous Mollusca [Philos. Trans. R. Soc. Lond. 143 (1853) pt 1: 29–66]. Discovery of the type or "idea" (in THH's sense, not Owen's or Agassiz's) is one of the highest ends of natural history.
position of heart in Cleodora.
Variability within species;
cementing process in cirripedes.
Down Farnborough Kent
My dear Sir
I have got out all the specimens, which I have thought could by any possibility be of
any use to you; but I have not looked at them, & know
not what state they are in, but sh
I am very much obliged for your Paper on the mollusca; I have
read it all with much interest; but it w
Is it not an extraordinary fact, the great difference in position of the heart in
different species of Cleodora? I am a believer that when any
part usually constant differs considerably in different allied species; that it
will be found in some degree variable, within the limits of the same
species:— Thus, I
I am very much pleased to hear that you have not given up the idea of noticing my Cirripedia volume. All that I have seen since confirms everything of any importance stated in that volume. More especially I have been able rigorously to confirm, in an anomalous species, by the clearest evidence, that the actual cellular contents of the ovarian tubes, by the gland-like action of a modified portion of the continuous tube, passes into the cementing stuff: in fact cirripedes make glue out of their own unformed eggs!.
Pray believe me | Yours sincerely | C. Darwin
I told the above case to Milne Edwards & I saw he did not place the smallest belief in it.—
- f1 1480.f1The date is established by the relationship to the letter to T. H. Huxley, 11 April .
- f2 1480.f2CD's collection of ascidians from the Beagle voyage (see letter to T. H. Huxley, 11 April ). He also enclosed notes extracted from his zoological diary of the voyage (DAR 30.2: 167–73).
- f3 1480.f3John Edward Gray, keeper of the zoological department, British Museum.
- f4 1480.f4T. H. Huxley 1853b.
- f5 1480.f5T. H. Huxley 1853b was primarily concerned with establishing an archetype for the cephalous Mollusca. Huxley, although using the term ‘archetype’ coined by Richard Owen, expressly distanced his particular usage from any idealistic connotations, stating (ibid., p. 50):
I make no reference to any real or imaginary ‘ideas’ upon which animal forms are modelled. All that I mean is the conception of a form embodying the most general propositions that be affirmed respecting the Cephalous Mollusca, standing in the same relation to them as the diagram to a geometrical theorem, and like it at once imaginary and true. For both Huxley and CD, the archetype of a class was suggested by comparative embryology and was a hypothetical structure representing general anatomical uniformities (see Correspondence vol. 4, Appendix II and di Gregorio 1984, pp. 22–35). Richard Owen and Louis Agassiz, on the other hand, believed in a Platonic archetype (see A. Desmond 1982, pp. 42–4).
- f6 1480.f6Huxley denied the existence of transitional forms between archetypes. ‘Anamorphism’, as he used the term, denoted a progression from a lower to a higher type, which he doubted ever occurred: ‘It may indeed be a matter of very grave consideration whether true anamorphosis ever occurs in the whole animal kingdom. If it do, then the doctrine that every natural group is organized after a definite archetype, a doctrine which seems to me as important for zoology as the theory of definite proportions for chemistry, must be given up.’ (T. H. Huxley 1853b, p. 63). See di Gregorio 1984, p. 33.
- f7 1480.f7See T. H. Huxley 1853, p. 42 and Plate IV.
- f8 1480.f8CD repeated this rule in Natural selection, p. 307, where he attributed it to George Robert Waterhouse (Waterhouse 1846–8, 2: 452 n. 1).
- f9 1480.f9See letter to T. H. Huxley, 11 April , and n. 9.
- f10 1480.f10Proteolepas bivincta, which CD classified as the sole species of a new order, Apoda. Proteolepas is now known not to be a cirripede. The observations on the cementing apparatus and process mentioned in this letter are described in Living Cirripedia (1854): 599–600. In T. H. Huxley 1857, Huxley stated that while he had not been able to trace the connection between the peduncular tubes and the cement gland, he nonetheless rather favoured ‘the conclusion that they are thus connected.’ (p. 239).
- f11 1480.f11See letter to J. D. Dana, 8 May , n. 5. In Living Cirripedia (1851): 38 n. and in Living Cirripedia (1854): 151 n., CD cited cases from the Crustacea of genera in which organs of the ovaria secrete a substance which served to attach the eggs to the parent's body, but he pointed out that these were only analogous to the situation he described in cirripedes.
- f12 1480.f12CD is referring to the 1849 meeting of the British Association for the Advancement of Science at which he commented on Albany Hancock's paper and which Henri Milne-Edwards also attended. In his report on Hancock's paper, published in the Athenæum (Collected papers 1: 250–1), CD remarked that the cementing substance of Cirripedia was ‘certainly secreted from glands which are actually continuous portions of the branching ovarian tubes or caeca’. To this Milne-Edwards ‘suggested that the secretion … was produced by a gland at the base of the antennae, similar to that which occurs in some species of macrourous Crustacea.’ CD ‘in reply stated that the gland in the cirripedes was truly ovarial.’ (Collected papers 1: 251).