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Darwin Correspondence Project

From John Davy1   30 January 1855

Lesketh How, Ambleside

Jany. 30— 1855

Dear Sir,

It will be a pleasure to me if I can give any aid on the subject of your letter which I received this morning.—

The expts. you suggest are I think very deserving of being made & I shall be glad to make them whenever I have an opportunity, which I can hardly expect to have till next spawning season,—I allude to that of the Salmonidæ.— Even then I cannot be sure of obtaining ova: this last season I have not succeeded in getting any.

In a paper containing miscellaneous observations on the Salmonidæ lately read at a meeting of the Royal Socy. of Edinburgh,2 I have mentioned one or two facts bearing I think on your inquiry.—3

One, the retention of life in a young Charr, (so small that might have been conveyed to a distance by a bird adhering to it’s feathers or feet), for the space of 72 hours, barely covered with water, so as to prevent it’s drying.—

Another, ova of the Salmon taken from the stomach of a trout, which proved to have been impregnated by the result, not losing their vitality; some of them, placed in water under favorable circumstances, producing young fish.—

From the expts. I have already made on the ova of fish I have little doubt that those at least of the Salmonidæ, are after impregnation very retentive of life, & that mere exposure to the air, provided they be kept moist, would not kill them.— They do not appear to suffer when exposed under the microscope, using a high power,—but on the contrary their development rather seems to be accelerated.— But what would be the effect of a partial drying according to your suggestion remains to be ascertained. I suspect it would prove fatal.—

I remain, | Dear Sir | Your’s very truly | John Davy. Charles Darwin Esqre.

CD annotations

crossed pencil
Top of first page: ‘18’4 brown crayon


Davy, an army surgeon and naturalist,was the brother of the chemist Humphry Davy.
CD had suggested experiments that might be performed to determine under what conditions fishes’ ova retained their vitality. He told Joseph Dalton Hooker that this was ‘in order to see how fishes’ ova might get transported’ (letter to J. D. Hooker, 7 April [1855]). For Davy’s results, see letter from John Davy, 21 March 1855, and Davy 1856.
CD’s portfolio 18 contained notes on geographical distribution.


Davy, John. 1854. Some observations on the Salmonidæ. [Read 18 December 1854.] Proceedings of the Royal Society of Edinburgh 3 (1850–7): 267–8.

Davy, John. 1856. On the vitality of the ova of the Salmonidæ of different ages; in a letter addressed to Charles Darwin, Esq., M.A., V.P.R.S. &c. [Read 7 February 1856.] Proceedings of the Royal Society of London 8 (1856–7): 27–33.


Responds to CD’s letter. The ova of Salmonidae exposed to air, if kept moist, will stay alive up to 72 hours.

Letter details

Letter no.
John Davy
Charles Robert Darwin
Sent from
Source of text
DAR 205.2: 227
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 1634,” accessed on 18 September 2020,

Also published in The Correspondence of Charles Darwin, vol. 5