Since our brief and imperfect sketch of metamorphosis appeared in Vol. V. of this series, Packard has treated the subject more fully in his Text-book of Entomology, New York, 1898; and Pratt has summarised the state of knowledge as to imaginal discs in Psyche, viii. 1897, p. 15, etc.
Monograph of Oestridae, Verh. Ges. Wien, 1863, and other papers op. cit. 1864, 1867, 1869; also Denk. Ak. Wien, xlii. 1880, xlvii. 1883.
Becher, Wien. Ent. Zeit. i. 1882, p. 49; for observation on connecting forms see Brauer, Verh. Ges. Wien, xl. 1890, p. 272.
The palpi are said to be of only one segment in some genera of Cecidomyiidae. The Cecidomyiidae are easily distinguished by the minute size—body not more than a line long—and by there not being more than six nervules at the periphery of the wing. Aëdes (Culicidae) has also short palpi.
It is said by Schiner that in the anomalous genus Nemestrina the palpi are of three segments.