D1PTERA. 451 



FAMILY II. 



TANYSTOMA *. 



THE Diptera of this family are distinguished from those of the two follow- 

 ing ones by the last joint of the antennae, which, exclusive of the seta which 

 may terminate it, presents no transverse division ; the sucker is composed of 

 four pieces. 



Their larvae resemble long and almost cyh'ndrical worms, with a constant 

 and squamous head, always provided with hooks or retractile appendages, by 

 which they are enabled to gnaw or suck the alimentary matters on which they 

 feed. They change their skin to undergo their second metamorphosis. The 

 nymphs are naked, and exhibit several of the external parts of the perfect 

 insect, which issues from its exuviae through a slit in the back. 



In our first division we find species whose proboscis is always entirely (or 

 nearly) salient, with the exterior envelope or the sheath of the sucker solid or 

 almost corneous, projecting more or less in the form of a tube or siphon, some- 

 times cylindrical or conical, and sometimes filiform, terminating without 

 any remarkable enlargement, the lips being small or confounded with the 

 sheath. The palpi are small. 



Some, that are rapacious, have an oblong body, the thorax narrowed before, 

 and the wings incumbent; their proboscis is most commonly short or but 

 slightly elongated, and forms a sort of rostrum. The antennae are always 

 approximated, and the palpi apparent. 



ASILUS, Linnceus, 



Where the proboscis is directed forwards. They fly with a humming noise, 

 are carnivorous, voracious, and, according to their size and power, seize on 

 flies, tipulae, bombi or Coleoptera, which they can exhaust by suction. Their 

 larvae have a small squamous head, armed with two moveable hooks, live in the 

 earth, and there become nymphs, whose thorax is furnished with dentated 

 hooks, and the abdomen with small spines. 



EMFIS, Linnaus, 



Closely allied to Asilus in the form of the body, and the position of the wings, 

 but with the proboscis perpendicular or directed backwards. The head is 

 rounded and almost globular ; the eyes very large. 



These insects are small and live on prey and the nectar of flowers. The 

 last joint of their antennae is always terminated by a biarticulated or short 

 stilet, or by a seta. 



* Long-mouthed. 

 G G 2 



