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Darwin Correspondence Project

To Ernst Haeckel   30 March [1868]1

Down Bromley Kent [4 Chester Place]

March 30

My dear Friend

I am much obliged for your interesting letter with its genealogical tree.2

I now understand to a certain extent the importance of the swim-bladder in the Selachians.3 I shall be curious to see whether the organ ought not to be considered rather in a “nascent” than in a “rudimentary” state. I had always imagined that some animal like the Lepidosiren was the parent-form of the Vertebrata.—4

By all means keep the German edition of my Book: it will be of far more use in your hands than in anyone’s else.—5

We have been staying nearly a month in London & I am as wearied of the din & turmoil of the place, as you could be; but we return in two days to the quietude of Down.6 My visit here has not been one of rest, for I have been hard at work in collecting new facts on Sexual selection, by corresponding with a multitude of breeders & visiting them & the zoological Gardens.

This subject will be the chief one in my next little book, for I entirely agree with you that sexual selection has played a most important part with man.7 But I find many very serious objections & difficulties & shall not make out a very good case.—

I am astonished at the hybrids of Hare & rabbit: is it certain that Dr Conrad began his work with a true wild Lepus timidus & not with a hare-like var. of the L. cuniculus?8

I am tired with writing letters, so will write no more, & will conclude with my unalterable esteem & friendship.—

Yours very truly | Ch. Darwin


The year is established by the relationship between this letter and the letter from Ernst Haeckel, 23 March 1868.
Lepidosiren is the genus of lungfish. CD had mentioned Lepidosiren as having affinities to very distinct groups in Origin, p. 330. For CD’s view of the difference between nascent and rudimentary organs at this time, see Origin 4th ed., pp. 534–7. Rudimentary organs were defined as remnants of a former state that served no present function, while nascent organs were the early stages of organs which would later attain functional status. CD emphasised that it was difficult to identify a nascent organ, since it was impossible to predict how any part would develop in the future.
The reference is to the German edition of Variation (Carus trans. 1868). See letter from Ernst Haeckel, 23 March 1868 and n. 3.
CD was in London from 3 March 1868 and returned home on 1 April (see ‘Journal’ (Correspondence vol. 16, Appendix II)).
CD refers to Descent.
Haeckel refers to Johannes Ernst Conrad (see letter from Ernst Haeckel, 23 March 1868 and n. 10).


Now understands importance of swim-bladder in selachians. Always imagined animal like Lepidosiren was parent form of vertebrates.

Has been nearly a month in London, collecting facts on sexual selection from breeders and at Zoological Gardens.

Astonished at hybrid of rabbit and hare. Is it certain that work was done with hare?

Letter details

Letter no.
Charles Robert Darwin
Ernst Philipp August (Ernst) Haeckel
Sent from
London, Chester Place, 4 Down letterhead
Source of text
Ernst-Haeckel-Haus (Bestand A-Abt. 1: 1–52/17)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 6070,” accessed on 29 June 2017,

Also published in The Correspondence of Charles Darwin, vol. 16