To George Rolleston   7 March [1861]1

Down Bromley Kent

March 7th

My dear Sir

Though you so kindly tell me not to write, you must let me have the pleasure of thanking you, busy as you are, for taking so much trouble to explain to me, the curious point of cyanosis & the clubbed nails.2 It may work in well, yet the case seems very complex.— I sincerely thank you.—

Yours very faithfully | ⁠⟨⁠Charles Darwin⁠⟩⁠3

How truly I agree with your remark on “borrowing organs” “prophetic types” &c &c!4

I hope you will work out the point about the mucus tubes; & I wish you could at same time work out the relation of the mucus tubes in Annelids with tracheæ of Insects. This has, always, seemed to me a curious case.5 | C. D.

1
Dated by the relationship to the letter to George Rolleston, 2 March [1861].
2
Rolleston had written to CD informing him of a correlation between clubbed finger nails and cyanosis (morbid blueness of the skin), and CD had asked him for further information on the subject (see letter to George Rolleston, 2 March [1861]). Rolleston’s reply has not been found.
3
The signature has been cut away.
4
Louis Agassiz discussed the concept of ‘prophetic types’ in the introductory volume of Agassiz 1857–62, pp. 116–18. There is an annotated copy of this work in the Darwin Library–CUL. Agassiz’s view was that extinct, fossil groups exhibiting combinations of characters now found only in distinct animal groups were evidence of a creator’s plan. For an earlier expression of CD’s negative opinion of Agassiz’s view, see Correspondence vol. 7, letter to T. H. Huxley, 13 [March 1859]. See also letter to Cuthbert Collingwood, 14 March [1861].
5
Rolleston was investigating the means by which certain lamellibranch molluscs distended their muscular feet, a process thought by some to involve the influx of water into a system of tubes homologous to the tracheae of insects. A paper on the subject by Rolleston and Charles Robertson was read before the Royal Society of London on 3 February 1859; CD may have read the abstract that was published (Rolleston and Robertson 1859). Further investigations led them to modify their views, which were published in a more detailed report (Rolleston and Robertson 1862).

Please cite as “DCP-LETT-3083,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-3083