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Darwin Correspondence Project

From Jeffries Wyman   8 January [1861]1

Cambridge [Massachusetts]

Jan 8th 1860

My Dear Sir

It gives me great pleasure to answer in so far as I am able your enquiries with regard to the rattlesnake.2 Dumeril & Bibron have given in their Herpetol. Generale,3 a somewhat confused description of the structure of the rattle & Czermack has published a memoir entitled “Uber den schallenzeugenden Apparat von Crotalus” Zeitsch. f. wissench. Zool. Vol VIII 1856.4 This last I have not seen, & only know it through the short account taken from it in Van der Hovens Zoology—5 As I have some good specimens of tails in alcohol, at the risk of sending you superfluous information, I shall give you some account of the examination of them, which I have been led to make by the questions contained in your last letter.

The first specimen is that of a foetus of Crot. durissus which was nearly mature, is nearly eight inches long, & was taken from the body of the parent. For this I am indebted to Prof Baird of the Smithsonn. Institution.6 On the tail of the foetus one rattle is already formed, fits the end of the tail very closely & has a somewhat different shape from the subsequent ones in the same species. It is a true cuticular covering & is continuous with the cuticle on the rest of the body.

The other specimens are from adults of C. rhombifer, & are fortunately in a condition to show very well one stage in the formation of the rattle. I will state first of all, that the last three caudal vertebrae are very much compressed laterally, anchylosed, & covered with a somewhat thickened layer of integument. The body thus produced has three prominent ridges as at a in the figure, & is the matrix on which the rattle is formed.

[DIAG HERE: 6.5cm]

In two instances a new joint or shell of the rattle has just been completed, but still fits tightly to the matrix in every direction, to which it sustains the relation of common cuticle. When mature the covering thus secreted becomes detached from the matrix over its whole surface, & is forced back in such a manner that it now grasps only the second & third ridges instead of covering all of them. In this way the free space between it & its successor is gained, as at b & c   I have never had an opportunity of witnessing the moulting of one of these snakes & cannot therefore describe the process by which the new formed joint is thus forced back— I suppose that in the first instance there is a shrinking of the matrix by which the rattle is detached & then, as each successive rattle is larger than its predecessor, the growth of the matrix which follows the separation pushes the rattle back. However this may be, one direct observation will be worth more than any or all suppositions. That the slipping of the rattle does take place I am sure, for numerous specimens which I have examined show it.

You mention the habit which the Trigonocephalus has, of vibrating its tail.7 Perhaps it will be no news to you, but I will mention at a venture, that our common blacksnake (Coluber constrictor) has the same habit, & when its tail is made to vibrate against dried leaves, the sound which is produced is quite startling from its resemblance to that of the rattlesnake. The sound of the blacksnake I have heard— I am also informed by others, among them by Prof Baird that there are several species in our western country which have the habit as well.

CD annotations

3.11 second & third ridges] ‘ridges’ added pencil
Top of first page: ‘(Prof? Wyman)’ pencil
On cover: ‘Lisotriton palmipes’ ink, del pencil; ‘Viperidæ | Penny Encyclop accounts of Fascination8 | Wyman says Black Snake rattles its tail.’ ink; ‘Ch VIII’9 brown crayon


The year is provided by the postmark: Wyman erred in writing ‘1860’.
See Correspondence vol. 8, letter to Jeffries Wyman, 3 December [1860]. Wyman, professor of anatomy at Harvard University, had begun a correspondence with CD at the suggestion of Asa Gray (see ibid., letter from Asa Gray, 23 January 1860).
Duméril and Bibron 1834–54.
Hoeven 1856–8, 2: 259–60.
Spencer Fullerton Baird was assistant to Joseph Henry at the Smithsonian Institution in Washington, DC.
See Correspondence vol. 8, letter to Jeffries Wyman, 3 December [1860]. CD described the vibrating tail of this snake, noting its curious resemblance to that of the rattlesnake, in Journal of researches, pp. 96–7.
CD refers to the article on American venom-snakes in the Penny Cyclopædia (1833–58), vol. 25–6, pp. 351–3, in which an account is given of the rattle as a device used to fascinate prey. See n. 9, below.
CD refers to chapter 8, ‘Difficulties on the theory of natural selection in relation to passages from form to form’, in his ‘big book’ on species. In the discussion of habits that appear to have been acquired by one organism for the good of another, which thereby stood in opposition to the tenets of natural selection, CD mentioned the vibrating tail of Trigonocephalus. CD suggested that this habit, rather than having been acquired to warn other animals, was ‘more likely to serve to paralyse by fear or fascinate its prey.’ (Natural selection, p. 383 and n. 1).


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Czermak, Johann Nepomuk. 1857. Ueber den schallenzeugenden Apparat von Crotalus. Zeitschrift für wissenschaftliche Zoologie 8: 294–301.

Hoeven, Jan van der. 1856–8. Handbook of zoology. Translated from the second Dutch edition by William Clark. 2 vols. London.

Journal of researches: Journal of researches into the geology and natural history of the various countries visited by HMS Beagle, under the command of Captain FitzRoy, RN, from 1832 to 1836. By Charles Darwin. London: Henry Colburn. 1839.

Natural selection: Charles Darwin’s Natural selection: being the second part of his big species book written from 1856 to 1858. Edited by R. C. Stauffer. Cambridge: Cambridge University Press. 1975.


Responds to CD’s inquiries about rattlesnake.

Letter details

Letter no.
Jeffries Wyman
Charles Robert Darwin
Sent from
Cambridge Mass.
JA 22 61
Source of text
DAR 89: 18–21
Physical description
† sketch

Please cite as

Darwin Correspondence Project, “Letter no. 3045,” accessed on 19 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 9