From H. W. Bates   22 March 1865

Royal Geographical Society | 15, Whitehall Place, S.W.

March 22 1865

My dear Mr Darwin

It gave me great pleasure this morning to see a letter in your handwriting showing that you had recovered your previous tolerably good state of health.1 The news will be welcome to all our friends when I tell them.

Pray do not send your copy of the Heliconidæ paper as I have still a few left & will send one to Mr Walsh,2 to whom I am indebted for copies of his papers lately arrived. I have read every line of his with great pleasure,—just a little deadened perhaps by the diffuseness of his style & want of closeness in his otherwise just reasoning.

I will make use of this opportunity to tell you of a small discovery of mine lately made in working out the species of a very long genus of Longicorn Coleoptera. It is with regard to the abrupt & profound modifications in sexual parts between very closely-allied species. You will perhaps recollect my telling you some time ago of a series of dissections made by a friend of mine of the male organs in Chrysomelidæ he having found great differences from species to species & even separated what were previously considered to be varieties, on the ground of modifications in these organs.3 In my Longicorns the parts in question are the accessory organs, that is the terminal abdominal segment from which the organ protrudes when necessary. The genus is Colobothea—one of those genera of which so many exist in all orders, in which the species seem to have been endlessly multiplied by nature. Nearly all the species can be distinguished by the form of the acessory organs in the sexes & I have found most profound modifications in what would be otherwise considered as local varieties. I have no doubt whatever that the species on dissemination over a wide area & breaking up into local varieties undergo modifications of these organs very readily & that this fact has operated greatly in the multiplication of species in nature for it is difficult to conceive the variously formed males of these closely-allied races to be equally adapted to their own females & to the females of their sister races. There is a physical obstacle here in the way of amalgamation with the parent or sister forms of segregated local varieties or races. I shall publish my notes on the subject in the Annals & Mag. Nat. Hist. in the course of my papers on Amazons Longicornes.4

Yours sincerely | H W Bates

I am expecting “cartes” by every post from my photographer & will send a pair on their arrival5

1
CD’s letter has not been found; however, it was evidently written after CD received the letter from B. D. Walsh, 1 March 1865 (see n. 2, below).
2
Benjamin Dann Walsh had written to CD that he was unlikely to find a copy of Bates’s paper on mimetic Lepidoptera (Bates 1861, the ‘Heliconidæ paper’) where he was living; he requested CD to ask Bates for ‘anything from his pen’ (see letter from B. D. Walsh, 1 March 1865).
3
The reference is to dissections made by Joseph Sugar Baly (see Correspondence vol. 9, letter from H. W. Bates, 18 March 1861 and n. 7, and Correspondence vol. 10, letter to H. W. Bates, 9 May [1862], and letters from H. W. Bates, 19 May 1862 and 14 June 1862). Chrysomelidae are a family of leaf-beetles. CD also discussed the morphology of the sexual organs of insects with Walsh (see Correspondence vol. 12, letters to B. D. Walsh, 21 October [1864] and 4 December [1864], and letter from B. D. Walsh, 7 November 1864, and this volume, letter from B. D. Walsh, 1 March 1865).
4
Bates had begun publishing his study of Amazonian longicorn or long-horned beetles in the May 1861 issue of the Annals and Magazine of Natural History (Bates 1861–6); he described species of the genus Colobothea in the issues for March, May, and August 1865 (Annals and Magazine of Natural History 15: 214–25, 382–94; 16: 101–8). For Bates’s discussion of the role of markedly different male sexual organs in the development of closely allied species, see ibid. 15: 388–9; citing Baly’s work on this topic, as well as his own, Bates added: The inevitable law of Natural Selection which governs the general process of the adjustment of the local races to new conditions will explain the changes of conditions of life in time; and the laws of variation, diversified in details as are the species themselves, will explain the rest.
5
A photograph of Bates is reproduced facing p. 121.

Please cite as “DCP-LETT-4792,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-4792