Verh. zool.-bot. Ges. Wien, xxxiii. 1883, p. 248.
Bonnet and Finot, Rev. Sci. Nat. (3) iv. p. 345. The word we have translated as humming is "bruissement."
De Saussure, Ann. Soc. ent. France, 1888, p. 151, pl. v. fig. 1.
Indian Mus. Notes, ii. 1893, p. 172.
Zoologist, 1867, p. 489.