Discusses rapid replacement of mates among birds. "I begin to think that the pairing of birds must be as delicate and tedious an operation as the pairing of young gentlemen and ladies. If I can convince myself that there are habitually many unpaired birds it will be a great aid to me in sexual selection". Notes rivalry of singing birds.

Heard from George Rolleston of the inherited effects of an eye injury.

Disagrees with A. R. Wallace’s idea "that birds learn to make their nests from having seen them whilst young" ["The philosophy of birds’ nests", Intellect. Obs. 11 (1867): 413–20].