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Darwin Correspondence Project

To Thomas Henry Huxley   17 July [1851]

Down Farnborough Kent

July 17th

My dear Sir

I beg to thank you for your very kind note of the 10th & your Report,1 which has interested me much, as I was ignorant & wished to learn about the metamorphoses of the Class in question.— I agree with your fundamental distinction between individuals & zooids,2 but I doubt whether it can be expected that creatures having so plainly the stamp of individuality as have many of your zooids will ever cease to be called individuals.

With many thanks | Pray believe me | Yours faithfully | Charles Darwin T. H. Huxley Esqe


T. H. Huxley 1851, a report on the investigations of Johannes Peter Müller into the anatomy and development of echinoderms.
Huxley had concluded his description of the development of echinoderms with a discussion of ‘one of the most comprehensive and interesting zoological theories of modern times— … “the alternation of generations.” ’ (T. H. Huxley 1851, p. 13). He believed that previous work, most notably by Johannes Japetus Smith Steenstrup and Richard Owen, raised philosophical difficulties about the nature and definition of an ‘individual’ in groups such as the echinoderms that have a succession of very different forms of larvae. Huxley therefore coined the term ‘zooid’ to describe a form that has an independent existence but that is only one of several successive forms that result from the development of a single ovum. In this case, the individual consists of the sum of the zooids; for example, according to Huxley: ‘Instead of saying then, that in a given species, there is an alternation of so many generations, we should say that the individual consists of so many zooids’ ( p. 15). See Winsor 1976, p. 65, and Farley 1982.


Thanks for report [on echinoderms, Ann. & Mag. Nat. Hist. 2d ser. 8 (1851): 1–19]. Wanted to learn about metamorphosis of the class. Agrees with THH’s distinction between individuals and zooids, but thinks zooids will never cease to be called individuals.

Letter details

Letter no.
Darwin, C. R.
Huxley, T. H.
Sent from
Source of text
Imperial College of Science, Technology, and Medicine Archives (Huxley 5: 2)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 1442,” accessed on 30 March 2017,