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Darwin Correspondence Project

To T. H. Huxley   13 [March 1859]1

Down Bromley Kent


My dear Huxley

Very sincere thanks for your note, which tells me everything which I wanted.2

I am very glad to hear about the serially modified & homologous parts in the Radiata. Your sketch of one of the Diphydæ or Physophoridæ seems as good a case as any plant. I cannot remember, (though such is my memory I may have read it lately & have forgotten it) any remarks on the serial homologies of the Radiata; & I was astonished at this & hoped it might be that there was not much indefinite repetition of homologous parts, but how I forgot such a case as Tænia & some of the others you allude to, I cannot tell. In my ignorance I had looked at Echinus & Asterias as a definite repetition of one whorl of only 5 quasi-leaves, like the two halves of the body in annelids or Vertebrates &c.—

I have to allude to this subject, because the ideal morphologies of naturalists, are on my notions, real changes in the course of time from one part or organ into another.3

With many thanks | Yours very truly | C. Darwin

I entirely agree with your remarks on Agassiz’s Essay on Classification: it is all utterly impracticable rubbish, about his grades &c &c.4 But, alas, when you read, what I have written on this subject, you will be just as savage with me.


Dated by the relationship to the letter to T. H. Huxley, 8 March [1859].
See Origin, pp. 437–8.
The reference is to the introduction to Louis Agassiz’s Contributions to the natural history of the United States (1857–62), which was reissued as a single volume in 1859 under the title An essay on classification. Agassiz sent CD a presentation copy of the earlier work (see letter to Louis Agassiz, 21 February [1858]), which is in the Darwin Library–CUL. CD had wished to discuss the work with Huxley in 1858 (see letter to T. H. Huxley, 24 February [1858]).


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.


Thanks for THH’s examples of serially modified and homologous parts in Radiata. Cannot understand how he forgot such cases.

Agassiz’s Essay on classification [1859] utterly impracticable rubbish.

Letter details

Letter no.
Charles Robert Darwin
Thomas Henry Huxley
Sent from
Source of text
Imperial College of Science, Technology, and Medicine Archives (Huxley 5: 258)
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 2430,” accessed on 24 May 2024,

Also published in The Correspondence of Charles Darwin, vol. 7