DIPTERA. 617 



ever, these organs become distinct, and the insect has then assumed the real state of pujia 

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

 ulien it makes its esca]ie. 



The larvi-e of dipterous insects arc dcstitu.e of feet, but some possess appendages which 

 resemble them. This is the only order in wliich 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 

 fiuniislied with two hooks, wliich serve them to gnaw their food. The principal organs of 

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

 tlic body ; many have also a pair on the segment immediately behind tlie 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 have 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 nortl) of France appears to me to be the 

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

 classification of the order, in two volumes, in the Suifes de Biijfhii, as well as a distinct vi'ork 

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

 British Diptera.] 



AVe divide this order into Ino principal sections, which form distinct orders in the works of 

 [several] English authors. 



'llie 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 jmpa state never takes place within the abdomen of the 

 parent fly. 



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

 of joints; they form 



THE FIi;.ST FAillLY OF THE DIPTERA,— 



The Nemocera, — 



The aiitenna3 of which are mostly composed of from fourteen to sixteen joints, or from six or nine to 

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

 longer than the head. Ttie body is elongated, with llie Iiead small and rounded; the eyes large; tlie 

 )Moboseis cxserted, short, and terminated by two laige lips, or prolonged into a beak ; t^\o external 

 ]ialpi inserted at its base, generally tilitorm or setaceous, and composed of four or tive joints ; the 

 thorax thick, elevated, and gibbose ; the wings olilong ; 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 tlie 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 larvie, always elongated and worm-like, have a sealy head, of a constant form, and the mouth 

 is furnished with parts analogous to maxillae, and lips. They al\A'ays shed their skins on assuming the 

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

 by the larva, apjiroach the perfect insects in their tigure, being fnriiisbcd with external organs, and 

 uiiclergoing their transformations in the ordinary manner. They have often near the heail and thorax 

 t^Ao respiratory organs, in the form of tubes, or ears. 



This family is composed of the genera Ciilej; and Tipula of Linnsus. 



Some have the antenna; always filiform, as long as the thorax, thickly clothed vitli hairs, and 



