The date is established by the address and by the reference to the volume of the Philosophical Transactions of the Royal Society of London (see below, n. 2). CD was in London at the home of his brother, Erasmus Alvey Darwin, from 3 to 10 March 1868 (Emma Darwin’s diary (DAR 242)). The only Monday during this time was 9 March.

The Philosophical Transactions of the Royal Society of London vol. 157 part 2, published in 1867, contained an article by Albert Günther on the anatomy of a lizard (Günther 1867). CD had evidently met Günther on 7 March 1868 at the British Museum (DAR 82: B10–11), and may have wanted to re-read the article. CD’s own copy of the article, in the unbound pamphlet collection at CUL, is annotated.