RECORD: Darwin, C. R. 1861. Gradation — Mr G. Sowerby. CUL-DAR48.A47. Edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed and edited by John van Wyhe 6.2025. RN1

NOTE: See record in the Darwin Online manuscript catalogue, enter its Identifier here. Reproduced with permission of the Syndics of Cambridge University Library and William Huxley Darwin. The volume CUL-DAR48 contains notes for Natural selection chap. 8 'Transitions of Organs'. Notes on bees' cells for origin of species theory.

A47

Gradation — Mr G. Sowerby Oct 17 /61/

Monomyaire & Dimyaire 2 main divisions — Etheria seems like a mono, but has 2 crescentic muscles — Mulleria (rare shell) has only one & more mediate with vestige of another at other end—

Gradation

(over)

A47v

Several bivalves have spiral umbo — gradation to Gasteropods & the operculum has spiral umbo.—

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Citation: John van Wyhe, ed. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)

File last updated 15 June, 2025