The year is established by the relationship between this letter and the letter to Francis Darwin, [31 August 1875 or later], which mentions proof-sheets of Variation 2d ed. The month and day are established by the reference to Francis’s impending arrival in Southampton on a Wednesday. CD was in Southampton from 28 August to 11 September 1875 (CD’s ‘Journal’ (Appendix II)). During this time there were two Wednesdays, 1 and 8 September. However, if Francis had been planning to visit early in CD’s stay there would have been little point in CD’s sending him the proofs, so Francis probably arrived on 8 September. This letter could not have been written before 1 September or the reference to Wednesday would have been misleading.

Francis was working on the proof-sheets of Variation 2d ed. (see letter to Francis Darwin, [31 August 1875 or later]).

Michael Foster had suggested that Francis work on the histology of the snail’s heart; Francis’s note was published in the Journal of Anatomy and Physiology in 1876 (F. Darwin 1876a). Proboscis work: see n. 4, below.

Amy was Francis’s wife; the friend has not been identified. Francis published a paper on the proboscis of Ophideres fullonica (‘an orange-sucking moth’) in the October 1875 issue of the Quarterly Journal of the Microscopical Society (F. Darwin 1875b). Ophideres fullonica is a synonym of Eudocima phalonia (the Pacific fruit-piercing moth).

CD was in Southampton from 28 August until 11 September 1875 (CD’s ‘Journal’ (Appendix II)).

Northam station was in Southampton; it was slightly closer to Bassett, where William Erasmus Darwin lived, than the central terminus.