DIPT ERA* 
It is afferted, that where large quantities cf them 
are found, the foil is generally marfhy, and the air 
unwholefome. 
(From BarbutJ Culex Pipiens . 
Thefe infefls, too well known by the feveral 
pun&ures they inflift, and the itchings thence 
ariling, afford a moft interefling hiflory. Before 
they turn to flying infefts, they have been in fome 
manner kibes, under two different forms. From the 
beginning of May till winter, fmall grubs may be feen 
with their heads downward, their hinder parts on the 
furface of the water, from which part arifes fide¬ 
ways a kind of vent-hole, or fmall hollow tube, like 
a funnel, and this is the organ of refpiration. The 
head is armed with hooks, that ferve to feize on 
infefls and bits of grafs, on which it feeds : on the 
hides are placed four fmall fins, by the help of which 
the infeft fwims about, and dives to the bottom. 
Thefe larvae retain their form during a fortnight or 
three weeks, after which period they turn to chryfa- 
lids. All the parts of the winged infefl are diflin- 
guifhable through the outward robe that fhroucls them. 
The chryfalids are rolled up into fpirals. The fitua- 
tion and fhape of the wind-pipe is then altered; it 
confiffs of two tubes, near the head, which occupy 
the place of the fligmata, through which the infedb 
is one day to breathe. It is a pleafmg fight to ob- 
ferve in a tub or glafs of water the motions of thefe 
i nfe £ls. 
The 
