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Darwin Correspondence Project

To T. H. Huxley   16 February [1863]1

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

Feb. 16th

My dear Huxley

I called twice in Jermyn St. but unfortunately found you once lecturing & secondly out.—2 It is by no means the carpal or tarsal bones which are increased in number, but generally only the digits & metacarpals.3 Indeed until the whole hand becomes doubled or bifurcated, it appears that the carpal bones are not increased. This same doubling puzzles me; but yet, I think, the wonderfully strong inheritance & thrice repeated growth shows that there is something in the case.4 May I say that the digits, (divided by many joints in the rays) are indefinite in number & very generally more than five in the pectoral fins of Fishes? How are Sharks &c in this respect? These being one of oldest orders would be best.—5

Now there is one other point, for which I shd. be very glad of information & bears on a remark made by you: I am told that Roget (no good authority) says in Bridgewater Treatise that in Frogs or Toads there is a rudiment of a sixth digit.6 Have you any specimen in spirits? I think I remember a tubercle behind. If there is one, could you spare time to dissect this tubercle & see whether in bone or other respect there is any reason to suppose that this really is rudiment of 6th digit. I have heard vaguely of two cases of six-toed frogs on hinder limb. If it should turn out a rudiment, you will, I know, allow me to quote you.

Ever yours | C. Darwin


The year is established by the relationship between this letter and the letter from T. H. Huxley, 20 February 1863.
Huxley was professor of natural history at the Royal School of Mines, Jermyn Street, London, and Hunterian professor of comparative anatomy at the Royal College of Surgeons (DSB). CD had taken breakfast with Huxley on 8 February 1863, while staying in London (see letter to T. H. Huxley, [8 February 1863]).
In his letter to Huxley of [8 February 1863], CD discussed the anatomical features of polydactylism. CD was collecting information on polydactylism for chapter 12 of Variation (see Variation 2: 12–14; see also letter to J. J. Briggs, 2 February [1863], and letter from James Paget, 7 February 1863 and n. 1). CD began writing a draft of the chapters on inheritance for Variation (ibid. 2: 1–84) on 23 January 1863 (see ‘Journal’ (Correspondence vol. 11, Appendix II)).
In his discussion of polydactylism in Variation (see n. 3, above), CD reported a privately communicated case of an additional digit in a child regrowing after two amputations (Variation 2: 14–15).
In Variation 2: 16, CD wrote: ‘fishes sometimes have in their pectoral fins as many as twenty metacarpal and phalangeal bones, which, together with the bony filaments, apparently represent our digits with their nails’. CD did not mention the case of sharks in Variation, but made the general point that the latent tendency to form additional digits in mammals, including humans, suggested reversion to ‘an enormously remote, lowly-organised, and multidigitate progenitor’ (Variation 2: 17).
The reference is to the ‘Bridgewater Treatise’ written by Peter Mark Roget, entitled Animal and vegetable physiology considered with reference to natural theology (Roget 1834, 1: 544). The ‘Bridgewater Treatises’ comprised eight works on natural theology published between 1833 and 1836 under the terms of a bequest made to the Royal Society of London by Francis Henry Egerton, the eighth earl of Bridgewater. According to the terms of the bequest, each author was to write and publish a treatise ‘On the Power, Wisdom and Goodness of God, as manifested in the Creation’ (EB; see also Topham 1993).


It is not carpal or tarsal bones that are increased [in six-fingered men] but generally only the digits and metacarpals.

Pectoral fins of fish and sharks.

Asks THH to check P. M. Roget’s statement that there is a rudiment of a sixth digit in frogs.

[P.S. missing from original.]

Letter details

Letter no.
Darwin, C. R.
Huxley, T. H.
Sent from
Source of text
Imperial College of Science, Technology and Medicine Archives (Huxley 5: 200)
Physical description
5pp & C 2pp

Please cite as

Darwin Correspondence Project, “Letter no. 3987,” accessed on 20 January 2017,