670 
and indeed the lymphatics of the part are fo large, as to 
exceed by far the fize of the fanguiferous veffels. The 
thoracic dudr, having patted under the oefcjphaguS from the 
right, runs on the infide of the vena cava of the left fide, 
receives a branch from its fellow of the oppofite fide, and 
joins the large lymphatics which lie on the left fide of the 
pericardium, and a part of thofe which lie behind the 
heart; and afterwards makes, together with the lympha¬ 
tics from the gills, upper fins, and fide, of the fifh, a net¬ 
work, from which a veffel pattes into the jugular vein of 
this fide. In a word, the lymphatics of the left fide agree 
exactly with thofe of the right iide above defcribed. Ano¬ 
ther part of the fylietn is deeper feated, lying between the 
roots of the fpinal procelfesof the back-bone. This part 
confifts of a large trunk that begins from the lower part 
of the fifit, and, as it afcends, receives branches from tire 
dorfal fins and adjacent parts of the body. It goes up 
near the head, and fends a branch to each thoracic duff, 
near its origin. 
The brain, in fifties is formed nearly in the fame way as 
that of fowls; only we may obferve, that the pofterior 
lobes bear a greater proportion to the anterior. Their or¬ 
gan of /melting is large; and they have a power of con¬ 
tracting and dilating the entry, into their nofe as they have 
occafion. It Jeeir.s to be moftly by their acute finell that 
t hey difeover their food; for their tongue feeriis not to 
1 1 five been defigned for a very nice fenfatkm, being of a 
firm cartilaginous fubftance; and common experience 
evinces, that their fight is not of fo much ufe to them as 
their finell in fearching for their nourifhment. If you 
throw a frcfli worm into the water, a fifh will diflinguilh 
it at a confiderable diftance; and that this is not done by 
the eye, is plain from obferving, that after the fame worm 
hits been a confiderable time in the water, and loft its odour, 
no fifties will come near it: but if you take out the bait, 
and make feveral little incifions into it, fo as to let out 
more of the odoriferous effluvia, it will have the fame ef¬ 
fect as formerly. Now it is certain, had the creatures 
diicovered this bait with their eyes, they would have come 
equally to it in both cafes. In confequence of their frriell 
being the principal means of difeovering their food, we 
may frequently obferve their allowing themfelves to be 
carried down with tiie ftrearn, that they may afce’nd again 
leifurely againft the current of the water; thus the odo- 
r iferous particles, fwimming in that medium, being applied 
more forcibly to their fmelling organs, produce a ftronger 
fenfation. 
The optic nerves in thefe animals are not confounded with 
one another in their middle progrefs between their origin 
and the orbit, but the one pattes over the other without 
any communication; fo that the nerve that comes from 
the left fide of the brain goes diftin&ly to the right eye, 
and vice verfa. Indeed it would feerri not to be neceffary 
for the optic nerves of fifhes to have the fame kind of 
connedtion with each other as thofe of mart have ; for their 
eyes are not placed in the fore-part, but in tiie (ides, of 
their head, and of confequence, they cannot fo conveni¬ 
ently look at any objeft with both eyes at the fame time. 
The lens oyjlallina is here a complete jphere, and more 
denfe than in terrefirial animals, that the rays of light 
coming from tiie water might be fufficiently refracted. 
As fifhes are continually expofed to injuries in the un¬ 
certain element they live in, and as they are in perpetual 
danger of becoming a prey to the larger ones, it was ne- 
ceffary that their eyes fhould never be flint; and, as the 
cornea is fufficiently wafhed by the element they live in, 
tiiey are not provided with palpebrae ; but then, as in tiie 
current the eye mu ft be expofed to feveral injuries, there 
was a necefiity that it fhould be fufficiently defended; 
which in effedt it is by a firm pellucid membrane, that 
leenis to be a continuation of the cuticula, being ftretched 
over here. Tire epidermis is very proper for this purpoie, 
as being ir.fenfible, and defiitutc of vellels, and confe- 
<] neatly not liable to obitruilions, or, by that means, of 
becoming opaque. In the eye of the Ikate tribe, there is 
[Comparative. 
a digitated curtain which hangs over the pupil, and may 
fhut out the light when tiie animal refits, and it is fimilar 
to the tunica adna of other animals. 
Although it was formerly much doubted whether fifhes 
pottetted a fenfe of hearing, yet there can be little doubt 
of it now ; fince it is found that they have a complete or¬ 
gan of hearing as well as other animals; and likewife, as 
the water in which they live is proved to be a good me¬ 
dium for the propagation of found. Fifhes, particularly 
thofe of tiie ikate kind, have a bag at fome diftance be¬ 
hind the eyes, which contains a fluid and a loft cretaceous 
fubftance, and fupplies tiie place of veftibule and coch¬ 
lea. There is a nerve diftributed upon it, fimilar to tiie 
portio mollis in man. They have femicircular canals, 
which are filled with a fluid, and communicate with the 
bag: they have likewife a meatus externus, which leads 
to the internal ear. The cod fifh, and others of the fame 
fhape, have an organ of hearing fomewhat fimilar to tiie 
former; but, inftead of a foft fubftance contained in the 
bag, there is a hard cretaceous ftone. In this kind of fifh 
no meatus externus lias been yet o'bferved. 
ANATOMY of INSECTS. 
With refpe6l to infefts and worms, they are fo exceed¬ 
ingly numerous, that it would be endlefs to examine all 
the different kinds, nor would it ferve any ufeful purpofe 
in this enquiry. We fhall therefore be content with ma¬ 
king a few-general obfervations, and thefe chiefly on the 
ftruChtre of their body. Inf efts differ from the former 
daffies, by their bodies being covered with a hard cruft or 
ficale, by their having feelers or antennae arifing from their 
head, and many of them breathing the air through lateral 
pores. As to the fhape of their bodies, though it fome¬ 
what differs from that of birds, being in general not fo 
fharp before, to cut, and make way through, tiie air, yet 
it is well adapted to their manner of life. The bafe of 
their bodies is not formed of bone, as in many other ani¬ 
mals, but the hard external covering ferves them for fkin 
and bone at the fame time. Their feelers, befide the ufe 
of cleaning their eyes, are a guard to them in their walk 
or flight. Their legs and wings are well fitted for their 
intended fervice; but the latter vary fo much in different 
infeCfs, tiiat from them natnralifts have given names to 
the feveral orders of the clafs. As, firft, tiie Colecptera, 
or beetle tribe, which have a cruftaceous elytra or flieli, 
that fliuts together, and forqns a longitudinal future down 
their Back. Hemiptcra: as incimex, cockroach, bug, &c. 
which have the upper wings half cruftaceous, and half 
membranaceous ; not divided by a longitudinal future, but 
incumbent on each other. Lepidoptcra: as the butterfly, 
have four wings covered with fine feales in the form of 
powder. Neuroptera: as tiie dragon-fly, fpring-fly, &c. 
have four membranaceous tranfparent naked wings, gene¬ 
rally reticulated. Hymenoptera: as wafps, bees, &c. have 
four membranaceous wings, and a tail furnifhed with a 
fling. Diptera; as tiie common boufe-fiy, have c,nly two 
wings. Aptera: as the lobfler, crab, feerpion, fpideiy &c. 
have no wings. 
The flructure of the eye in many infefts is a mod curious 
piece of mechanifm. The outer part is remarkably hard, 
to guard againft injuries; and has commonly a reticular 
appearance, or the whole may be confidered as an attem- 
blage of fmaller eyes ; but whether tiiey fee objects mul¬ 
tiplied before them, lias not yet been determined. 
Linnaeus, and feveral others following him, deny the 
exiftence of a brain in thefe creatures. But it is certain, 
that at leaf! a number of the larger kinds, as the lobfler, 
crab, &c. have a foft fubflance fimilar to the brain, from 
which the optic and other nerves take their rile; befides, 
when this fubftance is irritated, the animal is thrown into 
.convulfions: hence we fhould conclude, that infedls itave 
a brain as well as the former daffies, although this is fm'all- 
er in proportion to tiieir bodies. Their ear has been late¬ 
ly difco.vered to be placed at tiie root of .their antennas cr 
feelers, and can be diflinftly feen in fome of tiie larger 
kinds. 
ANATOM Y. 
