738 X C H T H } 
.thin membrane called the pericardium ; it varies in ftiape, 
according to the fpecies ; but contains two cavities : a ven¬ 
tricle, the (ides of which are very thick, wrinkled, and of¬ 
ten full of little holes; and an auricle, much larger, and 
before the left part of the ventricle, with which it com¬ 
municates by an orifice furnilhed with two valves. Here 
let us obferve, once for all, that the words before , behind , 
above, below, refer to the horizontal pofition of the fiffi. 
The blood is brought into the auricle before it is fent into 
the ventricle, which is by means of the vena cava, or at 
lead the extremity of that vein, called finus venofus, which 
lies in the hinder part of the auricle. The blood runs 
from the ventricle, through an orifice guarded by two- 
other valves, into an arterial fac, or large cavity, which 
might almoii be conlidered as a fecond ventricle; and 
which contracts when the heart dilates, and puffs up 
when the heart is compreffed ; its pulfations are manifefr ; 
when leflening in diameter, it forms a true artery, to 
which tiie name of aorta has been given: it is analogous 
to what is called the pulmonary artery in man and many 
other red-blooded animals. Its office is to carry blood to 
the gills, which ferve the office of lungs in fifties : for this 
purpofe it divides into two branches, running right and 
left to the gills on each fide ; and each of thefe branches 
breaks oft’ into as many minute fubdivifions as may be ne- 
celfary according to the number of gills and the branches 
and fringes in each. From the gills the blood is tranf- 
mitted to the other parts of the body. 
The mufcles of fillies do not differ confiderably from 
thofe of ether red-blooded animals. Their tendons are 
indeed inferted into the Ikin, which is not tiie cafe in 
man and moft quadrupeds; but the fame arrangement is 
obferved not only in ferpents which have feales, but alfo 
in the porcupine and hedgehog, which are covered with 
Ipines. The mufcles are eafily diftinguifhed by the ffiape 
of the fibres they confift of, and by their irritability. 
They more readily feparate into very thin fibres than the 
mufcles of more complex animals; and thefe fibrillte, how' 
minute loever, appear always flattened, and not cylindri¬ 
cal ; fo that they always exhibit two unequal diameters; 
which has not been remarked in the mufcles of man, qua¬ 
drupeds, birds, or reptiles. 
The principal mufcles of fillies are as follows : i. On 
each fide of the body, a mufcle ftvetches from the head to 
the extremity of the tail; this is compofed of feveral tranf- 
verfe mufcles, flrnilar and parallel to each other, Handing 
obliquely, a. The upper part of the body and tail is co¬ 
vered by two longitudinal mufcles, called dorfals, which 
occupy the. fpace between the lateral or fide mufcles. 
When there is a fin upon the back, thefe mulcles are in¬ 
terrupted or divided, confequently there are lour inftead 
of two; they-are fix in number if there are two dorlal 
fins, eight if three. 3. The lateral mufcles unite under 
the body; but under the tail they are feparated by two 
longitudinal mufcles, which are divided into two pair 
when there are two anal fins. 4.. There are feveral rauf- 
cles of different lizes about the head ; of the largeft, two 
are placed under the eyes, and two in the lower jaw. One 
alfo belongs to the membrane of the gills, and throws out 
a tendon to each ray by which that membrane is fuftained. 
3. Each peCtoral fin has two raifing-mufcles placed on the 
outer fnrfacq of thofe bones which have been compared 
to the collar-bone and fhoulder-blade, and two depreffing 
mufcles under the fame bones. The dorlal and anal fins 
have each four mulcles, two raifers and two depreflors. 
Each of the lower fins has three mufcles, one raifer and 
two depreflors. Four ftrong mufcles belong to the tail- 
fin : one ftraight and two oblique ones called fuperior ; the 
fourth, from its polition, is called, inlerior. 
The mufcles of fillies are more irritable than thofe of 
other animals which have red blood ; they yield more 
eafily to equal ftimuli. This is accounted for as follows: 
the mufcular fibres contain two principles, the earthy and 
the glutinous; and irritability feems to depend upon the 
greater proportion of the latter, as may be oblerved in the 
a 
O L O G Y. 
polypes, and young animals in general. This gluten, of 
oily nature,.pervades fiffi more than any other red-blooded’ 
animals. Their whole texture is pervaded by that oil fo 
well known in commerce and the arts, which is lecreted’ 
more particularly in tiie liver, and the extraction and pre¬ 
paration of which furnifhes fo much employment for the 
induftry of man, and fo much profit and convenience to 
repay that induftry. The oil is the caufe of the different 
degrees of tranfparency exhibited in confiderable portions, 
of the bodies of fifhes, even when pretty thick; and hence 
men have learned to give tranfparency to certain fub- 
ftanceS by impregnating them with oil, as for in fiance, 
oiled paper, which is often ufed inftead of glafs. The 
phofphoric light which fifhes emit arifes alfo from the oil; 
and this faculty does not leave them when they die. Some 
fifhes, in the torrid zone, appear at night like a lambent 
flame, as Adanfon obferved at Senegal; and, when num¬ 
bers of them are collected together, combining’ with other 
caufes which render the furface of the fea phofphoric, it 
is a moft magnificent fpectacle; but this oily matter;, 
which is one of the elements of fifties, emits a light fo 
ftrong as to be yifible on the furface when the fiffi is at a 
confiderable depth; Borda obferved this at the depth of 
feven metres, or three and twenty feet. But the oil has a. 
more eflential fervice, namely, to preferve the fifti un¬ 
changed amid the active element of water. 
But another vifeous fubftance, analogous to oil, yet 
different from it in many particulars, is elaborated in cer¬ 
tain veffels, carried under the external teguments, and 
fpread on the furface of the body through feveral aper¬ 
tures. The number, form, and pofition, of thefe apertures., 
canals, and fecretory organs, differ according to the fpe¬ 
cies ; but this humbur principally oozes through orifices 
on different parts of the head, and along the body and 
tail 011 each fide ; and thus is formed, according to Ce- 
pede, what we call the lateral line. This line is the more 
ftriking when the fiffi lias very vifible feales, becaufe it is 
formed then not only of the excretory pores- we have juft 
mentioned, but of a canal confiding of as many tubes as 
there are feales over thofe orifices, and hollowed out in, 
the fubftance of the feales themfelves. This line varies- 
in different fpecies from one to three on each fide; alfo 
in length, direction, bendings, interruptions, and the. 
fpines it may be armed with,. This vifeous fubftance, of¬ 
ten renewed, covers the whole exterior of the fiffi ; and 
hinders the water from penetrating the integuments ; it 
makes the body more lupple, and gives it the faculty of 
gliding with greater facility through the water, w hich this 
kind of varnifh feems to throw off. Animal oil, therefore*, 
which probably is the principle elaborated for the pro¬ 
duction of this gluten, aCts both directly and iridiredtly, 
both externally, and internally, upon fifhes; their molt 
compaCt and hard parts bear the marks of this their na¬ 
ture ; its influence and its effence pervade even the folid 
frame upon which reft all the foft parts we have been ex¬ 
amining. 
Th efciid parti are either cartilaginous or bony. They- 
make a compaCt whole fimilar to the fkeleton in other 
animals ; their interior ftrata are firft produced, and fir ft 
aCted upon by the different caufes of growth. But, when 
cartilaginous, they differ confiderably from, the bones of 
quadrupeds, birds, and men. Endued with a. mucofity 
which is the firft principle of the animal oil fo abundant 
in fifties, they are provided with cells, but not with any 
cavity properly fo called ; they do not contain that fub- 
itance called marrow of the bones in man, quadrupeds, 
and birds : they are a collection of lamince. And for this 
reafonLa Cepede has feparated the whole race of fi'fh into 
two grand divifions, the cartilaginous and the bony. The 
folids of the bony clafs greatly refemble thofe of other 
animals and men. 
Let us next examine the nervous fyjlem. The brain, in, 
which the nerves originate, is very fmall in proportion to 
the tize of the head in fifhes. In the common whale, for 
inftance, its weight is about the 25000th part of the total 
weight. 
