226 ad INSECTA. 
ticular, has well described them, and his work on the Diptera 
of the north of France published in the Mem. de la Soc. des 
Se. de l’Agricult. et des Arts, de Lille, of which he is one 
of the most distinguished members, surpasses, in my opinion, 
every thing hitherto published on this order of Insects. 
We will divide the Diptera into two principal sections, 
which in various systems of the English savans, even form as 
many particular orders. 
In those which compose the first, the head is always dis- 
tinct from the thorax, the sucker is enclosed in a sheath, and 
the hooks of the tarsi are simple or dentated. ‘The metamor- 
phosis of the larve into nymphs is always py after they 
have left the mother. 
In the first subdivision we find Diptera whose antenne are 
multi-articulated. 
FAMILY I. 
NEMOCERA. 
In this family the antennz usually consist of from fourteen to 
sixteen joints, and from six, or nine, to twelve, in the others. 
They are either filiform or setaceous, frequently hairy, par- 
ticularly in the males, and much longer than the head. The 
body is elongated, the head small and rounded, the eyes large, 
the proboscis salient, and either short and terminated by two 
large lips or prolonged into a siphon-like rostrum, with two 
exterior palpi inserted at its base, usually filiform or setaceous 
and composed of four or five joints. The thorax is thick and 
elevated; the wings are oblong ; the halteres are entirely ex- 
posed and apparently unaccompanied with alule. The ab- 
domen is elongated, and most commonly formed of nine annuli ; 
it terminates in a point in the female, but is thicker at the end 
and furnished with hooks in the nate The legs are very 
long and slender and are frequently used by these Insects to 
