Order 12. DIPTERA. 617 



ever, these organs become distinct, and the insect has then assnmed the real state of pupa 

 [inclosed within its old skin]. It scales off the anterior extremity of its cocoon, like a cap, 

 when it makes its escape. 



The larvae of dipterous insects are destitute of feet, but some possess appendages which 

 resemble them. This is the only order in whieh the head is soft and variable ;. but this cha- 

 racter is confined to such as are transformed beneath their own skin. The mouth is generally 

 furnished with two hooks, which serve them to gnaw their food. The principal organs of 

 respiration in the majority of the larvae of this order are placed at the posterior extremity of 

 the body ; many have also a pair on the segment immedjtately behind the head. 



Messrs. Fallen, Meigen, Wiedemann, and Macquart, have lately rendered signal service by 

 the establishment of numerous generic groups, by the description of many new species, or by 

 correcting the synonomy of those previously described. They ha^'e also employed the cha- 

 racters founded upon the arrangement of the nerves of the wings which I first used in my 

 " Genera." [Latreille here overlooks the previous claims of Harris.] 



The work of Macquart upon the Diptera of the north of France appears to me to be the 

 best treatise yet published on these insects. [M. Macquart has lately published a general 

 classification of the order, in two volumes, in the Suites de Biiffon, as well as a distinct work 

 on Exotic Diptera. Messrs. Haliday and Walker have added much to our knowledge of 

 British Diptera.] 



We divide this order into two principal sections, Avhich form distinct orders in the works of 

 [several] English authors. 



The Diptera of the first section have the head always distinct from the thorax, the sucker 

 inclosed in a sheath, and the tarsal claws simple, or unidentate. The transformation of these 

 insects from the larva to the j^upa state never takes place within the abdomen of the 

 parent fly. 



A first subdivision is composed of Diptera having the antennae divided into a great number 

 of joints; they form 



THE FIRST FAMILY OF THE DIPTERA,— 



The Nemocera, — 



The antennae of which are mostly composed of from fourteen to sixteen joints, or from six or nine to 

 twelve in others. They are filiform or setaceous, often villose, especially in the males, and much 

 longer than the head. The body is elongated, with the head small and rounded ; the eyes large ; the 

 proboscis exserted, short, and terminated by two large lips, or prolonged into a beak ; two external 

 palpi inserted at its base, generally filiform or setaceous, and composed of four or five joints ; the 

 thorax thick, elevated, and gibbose ; the wings oblong ; the balancers entirely exposed, and not 

 accompanied by large alulets ; the abdomen elongated, mostly formed of nine segments terminated in 

 a point in the females, thicker at the tip, and armed with hooks in the males ; the legs very long and 

 slender, and often enabling these insects to balance themselves. 



Many of the smaller species assemble in great troops in the air, where they form a sort of dance. 

 They are found at almost all seasons of the year. Many deposit their eggs in the water ; others in the 

 earth, or upon plants. 



The larvae, always elongated and worm-like, have a scaly head, of a constant form, and the mouth 

 is furnished with parts analogous to maxillae, and lips. They always shed their skins on assuming the 

 pupa state. These pupae, which are sometimes naked and sometimes inclosed in cocoons spun 

 by the larva, approach the perfect insects in their figure, being furnished with external organs, and 

 undergoing their transformations in the ordinary manner. They have often near the head and thorax 

 two respiratory organs, in tlie form of tubes, or ears. 



This family is composed of tlie genera Culex and Tipula of Linnaeus. 



Some have the antennae always filiform, as long as the thorax, thickly clothed with hairs, and 



