ICHTH 
weight of the fifh, the 38000th in the tunny, the 2500th 
in the fhark, the 2000th in the filurus, the 14.00th in the 
pike, the 600th in the carp ; whereas in man it is known 
to be about the 4.0th part ; in many quadrupeds, efpeci- 
ally the elephant, the 500th part, in the canary-bird the 
20th, in the cock and fparrow a 30th, in the eagle, the 
200th, in the goofe the 4.00th, in the adder, the Sooth, 
and about the 6'oooth part in the fea-tortoife. The brain 
in fifties is divided into lobes; the internal part is brown ; 
the exterior or cortical part is white and fatty. The fpi- 
nal marrow, which iflues from that organ, and whence 
all the' nerves, which do not run immediately from the 
brain are derived, extends along the back-bone to the ex¬ 
tremity of the tail ; yet not within the vertebras, which 
we have before obferved are not hollow, but over them, 
in a channel or gutter formed on purpofe. 
But the llrength of the nervous fyftcm does not entirely 
depend on the brain ; the fpinal marrow has a fliare in it; 
and it may be laid to refide in each feparate nerve ; for 
the farther we recede from man, in our approach towards 
infedts and worms, we fliall find the different organs more 
independent of each other. The nerves of fifties are as 
large in proportion as in the mammalia clafs, though pro¬ 
ceeding from a brain which is Ihialler. 
The adtion of the nerves produces the fertjes of fmelling, 
tailing, feeling, See, The organs o l fmell are very exten- 
five ; the noitrils are in general double, lituated between 
the eyes and the mouth, at a greater or lels diftance from 
the extremity of the Input. The nerves which act upon 
them are the firft pair coming immediately from the brain ; 
they are very thick, an.d, being divided in the noitrils 
into a great number of ramifications, multiply the fur- 
faces of the fenfitive faculty, and make it fulceptible of 
being adted upon by the flighted: impreftions. Thefe ra¬ 
mifications are more particularly fpread over thole nu¬ 
merous membranes which lie in two rows in molt of the 
cartilaginous fifties, efpecially the rays, but difpofed in 
radii in the bony kinds, and pervading the interior cavi¬ 
ties which contain the true organ of fmell. The water 
penetrates into thefe cavities, carrying with it the odo¬ 
rant particles it is loaded with: thefe orifices by which it 
enters are either fingle or double, round or oval : here it 
circulates, and then is repelled, for the admiflion of frefti, 
by the contractions and dilatations which the animal is 
capable of making in thefe organs.- 
As to the faculty of hearing, it is now generally agreed, 
beyond controverfy, that fifties have it; and in this re- 
fpedl we have come back to the opinion of the ancients, 
for both Ariltotle and Pliny held the lame thing; but it 
was afterwards contradicted, on account of the auditory 
organs not being immediately vifible. On this I'ubjeCl 
therefore we mult fay a few words. Thole animals who 
live continually in the water, and who receive the impref- 
fions of found through the medium of a fluid more denle 
than that of the atmofphere, exhibit neither, the outward 
organ of hearing, nor the membrane or cavity called tym- 
panjum, nor that pafft-ige from the infide of the mouth 
called the Eultachian tube, nor thofe auditory bones called 
incus, malleus, and Jlapss. Thefe parts are wanting, not 
only in fifties, but in many ferpents, in crabs, and other 
white-blooded animals, as the fepia, which Hill have an 
organ of hearing, and live in the midlt of the waters. But 
fifties have yet the organs necelfary for hearing, the parts 
of which are very obvious, very large, and very diltinCt, 
though hitherto little known. They were firft obferved 
fb long ago as 1-673, by Nicholas Steaton, of Copenhagen, 
who deferibed their principal parts; but their conftruc- 
tion' was not clearly known till very lately from the ex¬ 
periments of thofe celebrated anatomiits, . Geoffroy the 
Elder, Vicq d’Azyr, Camper, Monro, and Scarpa. We 
Shall firlt deferibe thefe organs in the cartilaginous tribes. 
The organ of hearing, like hat of fight, is double The 
two ears are contained in the cavity of the fkull, lying on 
each fide, at the angles moll dillant from the muzzle; and 
are. feparated only by a membrane from that, portion, of 
f O L O G Y. 739 
the cavity which contains the brain. The firft thing ob- 
fervable in the ear of many of thefe animals, is an open¬ 
ing formed by an elaftic membrane, or by a little cartilage, 
very fimilar to the fenejlra ovalis in man and quadrupeds. 
Next is perceived a veftibulum, which is'filled with a wa¬ 
tery liquor; and joining to this are three canals compofed 
of a membrane firm and thick, yet transparent; they 
are called femicircular canals, though they form nearly 
a complete circle ; and are very fimilar to the three mem¬ 
branous tubes in man and quadrupeds. (See Scarpa on 
the Senl'es of Animals.) Thefe tubes are enclofed in a 
cavity which is only a continuation of the veftibulum, 
and which they divide fo as to produce a fort of labyrinth ; 
they are larger in proportion than the correfponding tube 
in men and quadrupeds; being filled with a peculiar hu¬ 
mour, they fvvell out into the fiiape of phials, receiving 
the thin pulp of the acohftic ramifications, and mult 
be confidered among the real organs of hearing. Be- 
fides thefe three canals, the veftibulum contains three 
iinall facs, unequal in fize, confining, of a thin but firm 
and elaftic membrane, filled with a kind of thickened- 
jelly or lymph, and each containing one or two fmall 
cartilaginous bodies full of very minute nervous ramifi¬ 
cations, which may be confidered as the feat of lonorous, 
fenfation. 
The bony tribe, and fome of the cartilaginous, have 
no feneftra ovalis; but then them femicircular canals are 
longer, wider, and clofer together. They have only one 
membranous fac inftead of three ; but this one, which: 
contains one or two bodies of a bony or cretaceous Jub¬ 
ilance, is larger, and fuller of gelatinous matter; and in. 
the cavity where the femicircular canals meet, a fubltance 
is commmonly met with fimilar to what is found in the 
little facs. The ear of fifties, therefore, as well as of man,, 
quadrupeds, birds, and reptiles, has feveral receptacles or 
feats of found; but only one fenfation can be excited at 
once, becaufe all thefe receptacles are only emanations from 
a branch of the fifth pair of nerves, which in fifties is the- 
real acoultic nerve. 
As the tongue is generally fixed, and both that and the 
palate often filled up with clofe and numerous rows of 
teeth, it cannot be fuppofed'that their tajle is very exqui- 
fite ; but this is fupplied by the fmell, to which it feems 
to he transferred. 
The principal feat of the feeling feems-to be the lower 
part .of the belly and the extremity of the fnout. Thefe- 
two organs indeed cannot receive very lading or correct 
impreftions, becaufe they can. apply the belly or fnout. 
only to certain parts of the external furraces of bodies ; 
yet thefe organs are fufficient to give very lively impref- 
iton, and ftrongjy to warn the animal againit the prefence 
of any thing noxious.. Betides, thofe whole-lengthened 
bodies bring them to a: nearer fiefembiance with the fer- 
pent-tribe, and which have no vifible feales, can make 
feveral convolutions round an object; in that cafe, the- 
impreftions communicated by an increafed.fur-face mult, 
be more diftindt. We may hence conclude, that the feme 
of feeling in fifties is not fo imperfedt as it has been ge¬ 
nerally fuppofed ; and that there is no part of their body 
but is more or lefs endued'with this faculty : for who 
has not feen them dart like lightning from the hand which 
had touched or was near touching them? 
From what has been laid, and from what will appear in 
deferibing the different genera and fpecies of fifli, it is- 
manifeft that they poffefs their fenfitive faculties in the 
following order : 1. fmell; 2. fight; 3, hearing ; 4.. feel¬ 
ing ; 5.. tafte. No one can doubt but their principal fenle 
is fmell: by this inliindt they make immenfe journeys,, 
attradted by the odour of the prey they purfue,or repelled 
by that of the enemies they would avoid.. This may be 
called the lantern or eye of fifties ; it guides them amid ' 
the thickeft clouds of darknefs, againft winds and waves,, 
in the bofom of the molt troubled waters, and leaft perme¬ 
able to the rays of light. We know indeed that objedts 
may be difcerned.on a white.chalky bottom at the depth. 
