The year is established by the relationship between this letter and the letter from Henry Doubleday, 26 January 1857 (Correspondence vol. 6).

Doubleday’s letter has not been found. Doubleday suffered from frequent bouts of illness and depression and found writing difficult at times because of problems with his hand (Mays 1978, p. 75).

With his letter of 26 January 1857 (Correspondence vol. 6), Doubleday sent CD specimens of Peronea hastiana (an incorrect combination of Phalaena hastiana; a synonym of Acleris hastiana, the sallow button), a species of tortrix moth that has dozens of named forms. He also sent specimens of P. cristana (a synonym of A. cristana) and noted that all the named forms of tortrix moths would probably reduce into P. hastiana and P. cristana. CD had just completed chapter 4, ‘Variation under nature’, of his species book (Natural selection; see Correspondence vol. 6, Appendix II).