DIPTERA. 315 



bodj'. Several of tliem, besides, present two stigmata on the first 

 ring-, tliat 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 I first resorted, 

 with a corresponding nomenclature in my Genera. M. Macquart, in 

 particular, has Avell described them, and his work on the Diptera of 

 the north of France, published in the Mem. de la Soc. des Sc. de 

 I'Agricult. et des Arts, de Lille, of which he is one of the most dis- 

 tinguished members, surpasses, in my opinion, every thing hitherto 

 publislied on this order of Insects. 



We will divide the Diptera into two principal sections, Avhich 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 larvae into 

 nymphs is always effected after they have left the mother. 



In the first subdivision we find Diptera whose antennae are multi- 

 articulated. 



FAMILY I. 



NEMO CERA. 



In tliis family the antennae usually consist of from fourteen to six- 

 teen joints, and from six, or nine, to twelve, in the others. They are 

 cither filiform or 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 exterior 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 alulae. 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 fur- 

 nished with hooks in the males. The legs arc 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 form a sort of dance. They are found 



y2 



