DIPTERA. 
617 
ever, these organs beeome distinet, and the inseet has then assumed the real state of pupa 
[inelosed within its old skin]. It seales olF 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 which 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 j 
furnished with two hooks, which serve them to gnaw their food. The principal organs of I 
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 immediately 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 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 north of France appears to me to be the { 
best treatise yet published on these insects. [M. Macquart has lately published a general I 
I classification of the order, in two volumes, in the Suites de Buffon, as well as a distinct work | 
on Exotic Diptera. Messrs. Plaliday and Walker have added much to our knowledge of 
British Diptera.] 
We divide this order into two principal sections, which 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 pupa 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 ; tw'o 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 w^ater ; 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 the form of tubes, or ears. 
This family is composed of the genera Culex and Tipula of Linnaeus. 
Some have the antennae always filiform, as long as the thorax, thickly clothed with hairs, and 
