FLY 
FLY 
dage, and as fmooth as the common patellse or fea- 
limpets. 
There ar^ five fpecies of limaces, or fnails; there 
are three fpecies of the frefn-water neritae; there is 
one fpecies of the trochus ; there are three lipecies of 
the turbo i feven of the buccina; four of the dolia, 
or concha; globofs; and four of the cornu am- 
monis. 
Of the bivalve frefh-water fhells, there are five 
fpecies of the chamjE, and fix of the mufcle kind ; 
and of the pe6ten kind there is only one fpecies. 
Naturalills have not yet difcovered a fingle fpecies 
of the multivalve clafs. 
To reduce the feveral fpecies to their proper ge- 
nera, is not very difficult, from a recolleftion of 
the characters of each genus of marine fliells. The 
limpet is a fiat fhell, elevated into a fort of cone at 
the fummit. In the fnail kind, if the mouth be 
round, the fliell is a true limax; when femicircu- 
lar, the fliell is a nerita; and, when oval or de- 
prefied, and the clavicle long, it is then a trochus. 
The turbo, or fcrew-fhell, is known by it's long 
and (lender figure. The buccina are long-fhaped, 
tailed, and narrow-miouthed; and the dolia are 
fomewhat of a fubglobofe figure. The cornu am- 
monis and the umbilicated fnail are often con- 
founded together by thofe who obferve only their 
external refemblance among frefh-water fhells ; 
but in reality they are fufficiently diftinft, the cornu 
ammonis being externally marked with circular 
ridges, and divided internally into feveral feparate 
cells, like the common fofille kinds ; whereas the 
ymbilicated fnail is of an even external furface, and 
h^s only one internal cavity: the fnail alfo has it's 
mouth placed towards one fide, and the cornu am- 
monis in the middle. The chamae are known by 
their roundifh figure, and the mufcles by being 
oblong; and the peCten is diftinguifhed by it's 
ears and ftrije. 
FLY. A compleat defcription of the various 
clafifes, genera, and Ipecies, of Flies, conftitutes a 
very extenfive branch of natural hifcory. The 
number of the fpecies of Flies perhaps exceeds 
even that of the butterfly; but Flies being gene- 
rally very minute anim^als, lefs beautiful and lefs 
attraftive, naturalifts have not exerted their induf- 
try to reduce them to fuch determinate bounds as 
the former. However, the libelluls and the ci- 
cads, in magnitude and beauty, exceed many of 
the butterfly tribe; and tliefe have been obferved 
with attention, and defcribed with accuracy. 
In their original fl:ate, many Flies are either con- 
cealed from our view, or detained among very 
naufeous fubftances: it is only in their winged 
ftate that they become agreeable objeCts of our re- 
fearches ; and it may be proper therefore to begin 
their general hiftory in that ftage, occafionally de- 
fcending to an enumeration of their previous habi- 
tudes and natures, when the lights thrown on the 
fubjeft are fufficiently clear to direft us. 
It is generally believed, but certainly without 
foundation, that thofe minute Flies which we ob- 
ferve during fire vernal feafon will live and grow 
larger as fummer advances; but the fa6l is. Flies, 
like all other infeils which undergo a metam.orpho- 
fis, arrive at their full fize as foon as they become 
denizens of the fky; and, having fluttered through 
their contracted lives, and made provifion for po- 
fterity, they leave the ftage of exiftence to another 
fucceffion of animals. 
The general and mod obvious charafter of Flies, 
by which they are diftinguifhed from other winged 
infers, is in being furnifhed with tranfparent 
wings, totally free from the farina or duft vifible 
on thofe of butterflies ; and in having no cafes or 
covers for them. Thus, by this fimple charac- 
ter of having tranfparent and naked wings, they are 
clearly diftinguifhed from the butterfly, the beetle, 
the grafliopper, and other clafifes of winged in- 
fers. 
The principal parts or members of which Flies 
are compofed are, the head, the corfelet, and the 
body. To the corfelet the wings are appended; 
and in the body are contained the fl:omach, the in- 
tefl;ines, the parts of generation, and a confiderable 
part of the tracheje. The head is ufually united to 
the corfelet by a very fliort neck, on which it can 
often turn as on a pivot. Some Flies indeed have, 
as it were, the rudiments of tv/o corfelets, one fe- 
parated from the other; in which cafe, the firfc is 
ufually very fmall, and to the fecond the v^ings are 
affixed. The corfelet is the mod prominent and 
rounded part of the infect; it is always poflefTed of 
the greatefl: fl:rength, and is frequently the thick- 
eft: the Dragon-Flies, and fome v/ater-infefts, are 
of the kind which have double corfelets, or corfe- 
lets divided into two. 
The moft: obvious dIfl:in6lion for a claffical ar- 
rangement of Flies, is drawn from the number of 
their wings; fome having only two, and others four. 
Yet this plain and obvious divifion has not always 
been obferved by writers on natural hiftory; and 
fome have even negledled to inform us what numi- 
ber of wings belonged to the fpecies they were de- 
fcribing. 
The firft general divifion, therefore, of Flies, is 
into that of the two-winged and the four-v/inged 
kinds. A curfory view is generally fufficient to 
determine to which of thofe divifions a Fly be- 
longs; but if we afterwards examine the infeft with 
more attention, and confider the organs by which 
it receives it's nourifliment, it may be obferved 
that fome fpecies are able to protrude this organ to 
a confiderable diftance from their heads ; and that, 
when the Fly is in a ftate of reft, it is either folded 
up, fhortcned, convolved, or laid clofely down ; 
but, when the creature wants to ufe it, is unfolded^ 
lengthened, extended, or elevated. Naturalift's 
have given this organ the name of a trunk : but, in 
many fpecies of Flies, this appendage is wanting; 
and fuch have only an aperture ferving for a mouth, 
furrounded with lips and fome other parts. Some 
of thefe mouths have nothino; analoo;ous to teeth 
about them ; others, however, have teeth, fav/s, or 
grinders, placed externally, and moveable as in the 
caterpillar kinds, v/ith which the Flies tear and 
deftroy leaves, fruits, and fleflr ; and, laftiy, there 
are alfo fome Flies to which nature has allotted 
both a trunk and thefe organs. 
Thefe difl'erent charafters give us very naturally 
the diftinilions of four fubordinate claffes ynder 
the two former general ones. The firft clafs con- 
tains thofe which are furnifned with a trunk, but 
have no teeth or faws; the fecond comprehends 
thofe which have a mouth, without any apparent 
teeth ; the third, thofe which have a mouth fur- 
nifhed with teeth; and the fourth, thofe which have 
both a trunk and teeth. 
All the two-winged Flies belong to the two firft 
of thofe clafifes: the great blue Flefli-Fly, the fmall 
Flies which frequent our houfes, and the gnats, all 
being provided v/ith trunks without teeth, be- 
long to the firft clafs ; and the Spring.-Fly fo com- 
mon in gardens, and a fpecies of Fly refembling 
the 
