The year is conjectured from the relationship between this letter and the letter from Arthur Nicols, 20 August 1872 (Correspondence vol. 20). The context of the quotation is a discussion of Nicols’s ability to predict his own dogs’ behaviour from their expression, and the dogs’ own ability to communicate between themselves, and is introduced by the following words: ‘Some years ago I sent to the late Charles Darwin a number of cases bearing on this subject, and his reply was:’.