See letter from George Sim, 18 October 1879 and n. 1.

See Descent 1: 125 n. 38 and Descent 2d ed., pp. 36–7 n. 38. Otto Michael Ludwig Leichtenstern wrote that he had confirmed CD’s suspicion that supernumerary mammae in humans were reversions after he discovered in a review of more than 100 cases that 91 per cent occurred on the front of the thorax and in a predictable linear relationship with ordinary mammae (Leichtenstern 1878, p. 239). Leichtenstern’s paper was summarised in Kosmos in August 1878 (Kosmos 3 (1878): 443–7). CD’s copy of this issue of Kosmos is in the unbound journal collection in the Darwin Archive–CUL; it is lightly annotated, including with the words, ‘I have read the original paper somewhere’ (ibid., p. 447). CD’s offprint of Leichtenstern 1878, inscribed by the author, is in the Darwin Pamphlet Collection–CUL; it is not annotated.