DIPTERA, 315 
body. Several of them, besides, present two stigmata on the first 
ring, that which immediately follows the head, or replaces it. 
Messrs. Fallen, Meigen, Wiedemann, and Macquart, have lately 
rendered great service to this part of entomological science, by 
establishing various new genera, by describing a vast number of new 
species, and by rectifying errors relative to several of those previously 
known. They have also employed the characters presented by the 
disposition of the nervures of the wings, to which J first resorted, 
with a corresponding nomenclature in my Genera. M. Macquart, in 
particular, 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 
VAgricult. et des Arts, de Lille, of which he is one of the most dis- 
tinguished 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 distinct from 
the thorax, the sucker is enclosed in a sheath, and the hooks of the 
tarsi are simple or dentated. ‘The metamorphosis of the larve into 
nymphs is always effected after they have-left the mother. 
In the first subdivision we find Diptera whose antenne are multi- 
articulated. 
FAMILY TI. 
NEMOCERA. 
In this family the antennz usually consist of from fourteen to six- 
teen joints, and from six, or nine, to twelve, in the others. They are 
either filiform cr setaceous, frequently hairy, particularly 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 extericr palpi inserted at its base, usually fili- 
form or setaceous, and composed of four or five joints. The thorax 
is thick and elevated; the wings are oblong; the halteres are en- 
tirely exposed, and apparently unaccompanied with alule. The ab- 
domen is elongated, and most commonly formed of nine annuli ; it 
terminates ina point in the female, but is thicker at the end and fur- 
nished with hooks in the males. The legs are very long and slender, 
and are frequently used by these Insects to balance themselves. Se- 
veral, particularly the smaller ones, collect in the air in numerous 
swarms, and as they flit about forma sort of dance. They are found 
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