Note 13 — Chapter V · DOMESTIC PIGEONS.

This gland occurs in most birds; but Nitzsch (in his ‘Pterylographie,’ 1840, p. 55) states that it is absent in two species of Columba, in several species of Psittacus, in some species of Otis, and in most or all birds of the Ostrich family. It can hardly be an accidental coincidence that the two species of Columba, which are destitute of an oil-gland, have an unusual number of tail-feathers, namely 16, and in this respect resemble Fantails.