481 INSECTA. 



exterior, and inserted near the margin of the oral cavity, close to 

 which arises the sucker. 



The larvae, even of those in which the skin forms a cocoon for 

 the pupa (Stratiomis)^ retain their primitive form. 



This subdivision will comprise three families. 



FAMILY II. 



TANYSTOMA.(l) 



The Diptera of this family are distinguished from those of the two 

 following ones by the last joint of the antennas, 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 cylindrical worms, with a 

 constant and squamous head, always provided with hooks or retrac- 

 tile 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 is- 

 sues from its exuvias, through a slit in the back. 



In our first division we find species whose proboscis, always en- 

 tirely (or nearly) salient, with the exterior envelope or the sheath 

 of the sucker solid or almost corneous, projects more or less in the 

 form of a tube or siphon, sometimes cylindrical or conical, and 

 sometimes filiform, and terminates without any remarkable enlarge- 

 ment, the lips being small or confounded with the sheath. The 

 palpi are small. 



Some, that are rapacious, have an oblong body, the thorax nar- 

 rowed before, and the wings incumbent; their proboscis is most 

 commonly short or but slightly elongated, and forms a sort of ros- 

 trum. The antennae are always approximated, and the palpi ap- 

 parent. 



AsiLTTs, Lin. 

 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, Tipulse, Bombi or Coleopterae, which they then exhaust by 



(1) Long'-mouthed. 



