244 INSECTA, 
FAMILY II. 
TANYSTOMA. 
The Diptera of this family are distinguished from those of 
the two following ones by the last joint of the antenne, which, 
exclusive of the seta which may terminate it, presents no 
transverse division; the sucker is composed of four pieces. 
Their larve resemble long and almost cylindrical 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 metamor- 
phosis. The nymphs are naked, and exhibit several of the 
external parts of the perfect Insect, which issues from its 
exuvie, through a slit in the back. 
in our first division we find species whose proboscis, always 
entirely (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 eylindrical 
or conical, and sometimes filiform, and terminates without any 
pemicable 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 antenne are always approximated, and 
the palpi apparent. 
Asiwus, Lin. 
Where the proboscis is directed forwards. 
They fly with a humming noise, are carnivorous, voracious, aud 
according to their size and power, seize on Flies, Tipule, Bombi or 
