30 CLA SSIFICA TION OF DIP TERA . 



The Nematocera are very numerous, and are distinguished by their long- 

 jointed antcnn;p, which are sometimes plumose in the males. They are all 

 orthoraphic, and often have larva: with a well-developed head-capsule, some- 

 times invaginated within the thoracic segments (Tipula). They frequently 

 exhibit a transition between insects with a complete and an incomplete meta 

 morphosis, and have active nymphs ; the larva and nymph are also often 

 aquatic. The former, in the gnats, has a resemblance to the Zoea stage of the 

 Crustacea, and Fritz Miiller and Hiickel have suggested this as a probable 

 early ancestral form of the Insecta (Brauer).* The best-known genera are 

 Cecidomya, Chironomus, Corethra, Tanypus, Culex and Tipula. 



The Brachycera arc divided into Tanystomata and Muscaria by some, 

 but the sub-order presents exceptional difficulties ; perhaps the Tanystomata 

 should be furlhcr subdivided. 



The Brachycera arc all distinguished by having short antenucX, consisting 

 of three joints ; the third or terminal joint is largely dilated and contains the 

 olfactory organ. 



The Tanystomata all have a more or less developed head-capsule in the 

 larva, and have orthoraphic pup;v or naked nymphs, which escape from the 

 larval integument by a longitudinal dorsal fissure. The best-known forms 

 are Tabanus, Asilius, Bombylius, Empis and Dolichopus. 



The Tabanid;u, Asilida: and other orthoraphic Brachycera, when they arrive 

 at their final stage of development, closely resemble the cycloraphic Diptera, 

 but their larv;e exhibit a transitional condition between the eucephalic 

 ncmatocerous larva and the highly modified acephalic larva of the 

 Cvclorapliia. 



The Muscaria are the most highly modified Diptera; their larvae have 

 an incomplete head and a rudimentary internal head-capsule. They are all 

 cycloraphic, and are divided into Acalypterata and Calypterata. The former 

 have no wing-scales, and the latter, to which the blow-fly belongs, have large 

 wing-scales which cover the halteres. 



The Pupiparae are only separated from the Brachycera: by the remarkable 

 character of their metamorphosis. The young are developed singly within 

 the uterus of the mother, which deposits young pup;u instead of eggs ; thus 

 there is no true larva stage, but a gigantic embryo is transformed directly 

 into a pupa. They are all parasitic, and are the Nycteribipe, Hypoboscida^, 

 and Braulida;. The two first are parasitic on birds and mammals, and the 

 last on bees. 



The genera of the Muscida: are exceedingly numerous, and include about 

 one third of the Diptera ; many differ by small, and apparently unimportant, 

 details. 



Musca. — The old genus Musca has been divided and subdivided. Now 

 it is much restricted by the formation of new genera ; so that in the latest 

 catalogue of ]5ritish Dipteraf it includes only two species, the house-fly 

 {Musca doinestka) and the small house-fly (/I/, corvina). The flesh-flies 

 {Sarcopliaga) form a distinct family, and the blow-flies constitute the three 

 subgenera, Lucilia, Calliphora, and Pollenia. 



* Verb. Zool.-Bot. Gesellsch.. Wien, Bd. xix., p. 301. 



t 'A List of British Diptera,' by G. H. Verrall, small 4to, London, 1888. 



