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Darwin Correspondence Project

From William Thierry Preyer   [before 17 February 1870]1

interest for your theory, viz:

1) The chemical and other differences of the blood-crystals (hæmoglobine) according to the species from which the blood is taken— this astonishing fact—proves that natural selection acts not only on the morphological development, but even on the purely chemical constitution of organs. The red colouring matter of the blood, although it always shews the same spectrum, is a different substance in every species.2

2) The intimate relation between the sensations of sound & colour corroborate your statements (Variation etc II, p. 328, 1868).3

3) The occurrence of sulphuric acid in a free state in the glands of Dolium galea confirmed by my analysis is a case of wonderful adaptation (not yet quite understood). It may be compared to the exceptional development of electric organs (in torpedo etc).4

4) The noxious effects of prussic acid on animals are very instructive shewing: 1o. how great are the individual differences within the same species; 2o. surprising resemblances between the symptoms of warm-blooded vertebrates & true insects and again between cold-blooded vertebrates & mollusca.5

You would very much oblige me by occasionally informing me what relation of yours is Robert Waring Darwin mentioned by Göthe (Farbenlehre, Works Vol xxxix, p. 404–408). He wrote “On the ocular spectra of light and colours” (phil. trans. Vol. 76. Nov. 1785) reprinted in your celebrated grandfathers “Zoonomia”.6

I should very much like to know whose lectures you heard at Edinburgh & Cambridge besides Dr. Grants & Rev. Henslows.7 & which book or books made deep impressions on you in youth.

But this letter is already too long.

I remain | your’s truly | Wm. Preyer

CD annotations

3.1 2) The intimate … etc). 4.4] crossed pencil
6.1 You … long. 8.1] crossed pencil


The date is established by the relationship between this letter and the letter to W. T. Preyer, 17 February [1870].
Preyer sent CD a copy of his paper on haemoglobin (Preyer 1868); there is a copy in the Darwin Pamphlet Collection–CUL.
Preyer sent CD a copy of his paper on sound and colour (Preyer 1870a); there is a copy in the Darwin Pamphlet Collection–CUL. In Variation 2: 328, CD wrote, ‘The organs of sight and hearing are generally admitted to be homologous, both with each other and with the various dermal appendages; hence these parts are liable to be abnormally affected in conjunction.’
The snail Dolium galea secretes sulphuric acid. For a brief account of Preyer’s work, see Sitzungberichte der Niederrheinischen Gesellschaft für Natur- und Heilkunde (1866): 6–9. CD discussed electric organs in fish in Origin, pp. 192–3.
Preyer published on this subject in Preyer 1869.
Preyer refers to R. W. Darwin 1786, and to Erasmus Darwin’s Zoonomia (E. Darwin 1794–6). For Johann Wolfgang von Goethe’s Farbenlehre, see Goethe 1989; the discussion of Robert Waring Darwin is on pp. 875–8 of this edition.
CD had mentioned Robert Edmond Grant and John Stevens Henslow in his reply to Preyer’s biographical questions (see Correspondence vol. 17, letter to W. T. Preyer, [before 21 March 1869]).


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

Darwin, Erasmus. 1794–6. Zoonomia; or, the laws of organic life. 2 vols. London: J. Johnson.

Darwin, Robert Waring. 1786. New experiments on the ocular spectra of light and colours. [Read 23 March 1786.] Philosophical Transactions of the Royal Society 76: 313–48.

Goethe, Johann Wolfgang. 1989. Zur Farbenlehre. Edited by Peter Schmidt. Vol. 10 of Johann Wolfgang Goethe. Sämtliche Werke nach Epochen seines Schaffens. Munich: Carl Hanser Verlag.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Preyer, William. 1868. Ueber einige Eigenschaften des Hämoglobins und des Methämoglobins. Archiv für die gesammte Physiologie des Menschen und der Thiere 1: 395–454.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.


Notes the differences in haemoglobin between species; this proves, to WP, that natural selection does not act only on morphological development.

Remarks on the differences and similarities in the effects of prussic acid on different groups of animals.

Questions CD on his early education and influences.

Letter details

Letter no.
William Thierry (William) Preyer
Charles Robert Darwin
Sent from
Source of text
DAR 261.11: 21 (EH 88206073)
Physical description
2pp inc †

Please cite as

Darwin Correspondence Project, “Letter no. 7110,” accessed on 25 January 2021,

Also published in The Correspondence of Charles Darwin, vol. 18