30 CLA SSIFICA TION OF DIP TERA . 



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

 jointed antennte, 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 are divided into Tanystomata and Muscaria by some, 

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

 should be further subdivided. 



The Brachycera are all distinguished by having short antenna?, 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 pupa; 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 Tabanida;, AsilidcC and other orthoraphic Brachycera, when they arrive 

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

 but their larvje exhibit a transitional condition between the encephalic 

 nematocerous larva and the highly modified acephalic larva of the 

 Cycloraphia. 



The Muscaria are the most highly modified Diptera; their larvce 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 Pupiparse are only separated from the Brachyceric by the remarkable 

 character of their metamorphosis. The young are developed singly within 

 the uterus of the mother, which deposits young pupte 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 Nycteribite, Hypoboscida?, 

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

 last on bees. 



The genera of the Muscidje 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 British Dipteraf it includes only two species, the house-fly 

 {Musca domesticd) and the small house-fly (Af. corvind). The flesh-flies 

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

 subgenera, Lucilia, Calliphora, and Pollenia. 



* Verh. Zool.-Bot. Gesellsch., Wien, Bd. xi\., p. 301. 



t 'A List of British Diptera,' by G. H. Verrall, small 4to, London, 1S88. 



