O Y S O Y S 
t5>2nng the ficHi, are fatisfied with living on the 
inarrcr contained in the abfcefs, and give the ani- 
mal no great degree of pain. 
A mo'derate preffure is always fufficient to dif- 
lodge the worms from thefe tumours : they eafiiy 
make their appearance by the hole of the cxcref- 
ccnce, which, though fmall, is fufficient for this 
purpofe. As foon as the worm is emancipated, 
either by accident or in the courfe of nature, 
from it's habitation, it immediately drops on the 
ground, where crawling about till it can find a 
place proper for repofe, it takes up it's refidence 
there, and undergoes it's feveral transformations. , 
When thefe animals have found places to reft 
in for their changes, they lofe all motion ; and 
their fl<ins become hard and black, forming a kind 
of fhells, which ferve to protect theiri from thofe 
numerous accidents to which fuch minute crea- 
tures are continually expofed. 
The time of the Fly's egrefs being arrived, it 
appears indeed with two wings, but fo extremely 
like the middling- fized humble bee's, that it is not 
eafiiy diftinguiflied from them : however, when 
clofely examined, this fly appears to haveamouth, 
without teeth or lips ; fhort antennse, rounded 
at the extremities, and of a gloflTy hue; and reti- 
cular eves of a deep chefnut-colour. The female, 
in the under and hinder part of her body, has a 
cylindric tube, which fhe can protrude at plea- 
fure; and with this inftrument fhe pierces the fkin 
of the animal, in order to depofit her egg. 
It may alfo be obferved, that ftags, and fome 
other animals, are fubjeft to thefe worms in the 
fame manner as oxen and the feveral ftates they 
undergo in the tumours of thefe animals, are exadlly 
Umilar to what have been already mentioned. 
OXYRYNCHUS. A fi.lh of the truttaceous 
kind, called bylbme hautin and outin. It is fre- 
quently caught in the Englifh and uthtrrfeas; and 
or1:en mixed v/ith whitings, and expofed to fale 
along with them. In fhape and figure, it refembles 
the trout; but is Ibmevv'hat flatter, and covered 
widi large white fcales. 
OYSTER. A very large genus of fhells, the 
charafters of which are; that the fhell is bivalve, 
of a very coarfe external fl:ru£lure, and dirty ap- 
pearance; each fhell being compofcd of a great 
number of laminae irregularly clofed down on each 
other. In fome fpecies, it is fmooth; in others, 
ftriated, tuberous, or prickly; ufually flat, but 
fometimes globofe, plicated, and wrinkled into 
fmufes; the lower fhell being always the deepeft. 
The inciofed animal is a tethys. 
L.innjEus enumerates thirty-one fpecies under 
this genus ; which may be all arranged under the 
characters of fuch as are plain and fmooth, fmooth 
but foliated on the furface, globofe v/ith fpines, 
globofe and jagged with high-raifed laminse, and 
oblong and um.bonated. 
In many refpeds, the Oyfler difl^ers little from 
the mufcle, except in the thicknefs of it's fliell, 
and it's gieater imbecillity. The Oyfler, like the 
mufcle, is formed v/ith organs of life and refpira- 
cion; with inteftines which are very voluminous, 
a liver, lungs, and heart. Like the mufcle, it is 
felf-impregnated ; and the fhell, which the ani- 
mal foon acquires, ferves it for it's future habita- 
tion. Like the mufcle, it opens it's fhell to re- 
ceive the influx of water; and, like that animal, 
is ftrongly attached to it's fhells both above and 
below. However, in miany particulars it differs 
from the mufcle. In the firft place, it's Hidh are 
not equal, the one being cupped, the other flat: 
and on the cupped fliell it is always feen to reft; 
for if it refled on the flat fide, it would foon be 
drained of it's inciofed fluid. It differs alfo in 
the thicknefs of it's fliells, which are fo flrongly 
lined and defended, that no animal will attempt 
to pierce them. But though the Oyfter is fecured 
from the attacks of the fmall reptiles at the bot- 
tom, yet it often ferves as an obje6t to v/hich they 
are attached. Pope-worms, and other fmall ani- 
mals, aflix themfelves to the Oyfler's fides, and 
in this manner continue to live in perfe6l fecu- 
rity. Amiong the number of thefe adherents, 
there is a fmall red worm, often found on the 
fliell ; which fome have erroneoufly fuppofcd to 
be the male by v/hich the fpawn was impregnated. 
I'he Oyfter likewife differs from the mufcle in 
being utterly unable to change it's fituation. The 
mufcle is capable of erecting itfelf on an edge, 
and proceedingwith a flow laborious motion ; while 
the Oyfter is wholly paffive, and endeavours with 
all it':^ might to continue fixed to one fpot at the 
bottom. Rocks, ftones, pieces of timber, or fea- 
weeds, all feem adapted to give it a fixture, and 
to fecure it againft the agitation of the v/aves. 
Nothing is more common, in the rivers of the 
tropical climates, than to fee Oyfliers growing 
even amid the branches of the foreft. Many trees 
which grow along the margins of the flreams, 
bend their branches into the v/ater; and particu- 
larly the mangrove, which chiefly delights in a 
moift fituation. To thefe the Oyfters hang in 
clufters, like apples on the mott fertile tree; and, 
in proportion as the weight of the fifh finks the 
plant into the v/ater, where it ftill continues grow- 
ing, the number of Oyfters increafe, and arrange 
themfelves on the branches. Indeed, thefe flicll- 
fifli will attach themfelves to any fubflance, and 
even to each other: this is efTecl d by means of 
a glue peculiar to themfelves, which, when it ce- 
ments, the joining is as hard as the fhell, and is 
broken with as much difficulty. The joining fub- 
flance, however, is not always of glue: but the 
animal grows to the rocks, fomewhat like the 
mufcle, by threads ; though thefe are only feen to 
take root in the fliell, and not, as in the mufcle, 
to fpring from the body of the fifh itfelf. 
The Ipav/n of Oyflers, which is ufually caft in 
May, appears at firfl like drops of candie-greafe, 
and adheres to any hard fubflance on v/hich it 
happens to fall : this is covered with a fhell in tv/o 
or three days; and in three years time the animal 
is large enough to be brought to marker. As it 
invariably remains in the place where the fpawn is 
firfl: dropped, and grows without any other feem- 
ing food than the aftlux of fea-water, it is the 
cuilom at Colchefler, and other parts of the king- 
dom where the tide fettles in marflies on land, to 
pick up great quantities of fmall Oyfters along the 
fliore, which, when firfl collefted, are no broader 
than a fixpence: thefe are depofited in beds with- 
in the reach of the tide, and in two or three years 
grow to a tolerable fize. T!iey are faid to be 
improved in their flavour by being thus flickered 
from the agitations of tlie deep; and a mixture 
of frefh-water entering into thefe repofitories, pro- 
bably alTifls their growth, their fatnefs, and their 
tafl:e. 
Oyfters, however, which are prepared in this 
m.anner, are by no means fo large as thofe fouiid 
flicking to rocks at the bottom of the fea, ufually 
called rock-oyfters : rhefc are fometimes eight oV 
^ nine 
