ICHTHYOLOGY. 
547 
and which fills rivers, lakes, and ftreams, at certain fea- 
fons, with fi(h which all the reft of the year inhabit the main 
ocean, which arifes from the lame and other cdufes. Thefe 
return as regularly to the places whence they came ; and 
this is the aft of entire fpecies. But we mull not con¬ 
found among thefe periodical journeys other appearances 
of a different nature; fuch are the migrations fuppofed to 
take place in the mackarels and herrings. They have 
been del'cribed as coming in clofe columns, in order of 
battle as it were, and headed by chiefs or leaders. The 
faft is nothing more than this : the mackarels and her¬ 
rings live for the greater part of the year in the depths of 
the main ocean, and at certain feafons they rife to the fur- 
face, and approach the Ihores that are neareft to their 
abodes, and belt fuited to their purpofes and defires. 
Thefe journeys, whether periodical or accidental, are 
executed with great celerity and with little reft. Some 
bave been known to accompany Ihips in long voyages, 
e. g. from America to Europe; have kept up with them 
conftantly in fpite of winds and florins; fometimes get¬ 
ting before them, fporting about and then returning; 
then, after a Ihort repofe, fetch up their loft time, and ar¬ 
rive on the coafts of Europe with the Ihips. It is faid 
that the falmon can fwim in calm weather at the rate of 
near twelve miles an hour. 
Yet filhes have need of reft, and even of deep. - When 
beginning to be lleepy, their fwimming-bladder is dwelled 
out, and filled with a very light gas; they can glide with¬ 
out effort in the middle of the water, and enjoy a peace¬ 
ful Humber undilturbed by a gentle and involuntary mo¬ 
tion. Yet their mufcles are too irritable to permit them 
to deep foundly unlefs retting on a folid fubftance, during 
the ftillnefs of night, or in a dark retreat, far below the 
furface of the water, and where fcarcely any rays of light 
may reach their eyes, which are always open. 
The inltinft of filhes is ftronger than generally fup¬ 
pofed, if it be true, as many authors affirm, that they can 
be tamed and rendered familiar. It is well known, fays La 
Cepede, that, in the gardens of the Thuilleries, filh have 
been kept in refervoirs for more than a hundred years, 
which would come when called, and efpecially if called 
by the name they had been accuftomed to; and in the 
ponds of Germany they have been taught to come at the 
found of a bell to take their food. It is obferved that 
thofe fpecies which could not otherwife get the nourilh- 
ment they prefer in thofe ponds, are mod: ealily tamed. 
Filhes form the fourth clafs of animals in the Linnaean 
fyftem. They are arranged into fix orders ; the four firft 
of which are diftinguilhed by the poiition of the ventral 
fins, and by having bony rays to the gills ; the two laft 
have cartilaginous rays to the gills. As to the number of 
genera, Gmelin, in his edition of Linnaeus, has given us 
66, and 834 fpecies. Bloch has 81 genera; but, as he 
only defcribed thofe he was able to give figures of, his 
fpecies amount to only 523. Cepede has lb fubdivided 
the whole genera, belides adding new ones, that his five 
volumes contain 223 genera, and 1463 fpecies, indepen¬ 
dently of the cetaceous filhes, which he has defcribed in 
a feparate volume. The generic characters are taken from 
the lhape of the body, covering, ftrufture, figure and parts 
of the head, but principally from the branchioftegous 
membrane. The fpecific characters are taken from the 
cirrhi, jaws, fins, fpines, lateral line, digitated appendages, 
tail, and colour. 
ORDERS and GENERA. 
I. Apodes. The characters of this order are, gills with 
bony rays, and no ventral fins. The genera are thirteen: 
Murasna. - - Aperture of the gills at the tides of the 
thorax. 
Synbranchus. - A fingle branchial aperture under the 
throat. 
Sphagebranchus.- A double branchial aperture under the 
throat.. 
body thin, much 
Gymnotus. - - Dorfal fin none. 
Leptocephalus. - Peftoral fin none; 
compreffed. 
Trichiurus, - - Caudal fin none ; body enfiform. 
Anarhichas. - Teeth rounded. 
Ammodytes. - Head narrower than the body. 
Ophidium. - - Body enfiform. 
Xiphias. - - Snout enfiform. 
Stromateus. - Body oval, fcaly; breaft limple. 
Sternoptyx. - Body oval, naked ; breaft folded. 
Stylephorus. - Eyes placed on a Ihort cylindrical pe¬ 
duncle. 
II. Jugulares. The characters of this order are, bony 
rays to the gills; the ventral fins placed at the throat,, 
nearer to the mouth than the peftoral fins. There are fis 
genera : 
Callionymus. - Aperture of the gills on the nape, 
Uranofcopus. - Head large, rough, depreffed. 
Trachinus. - - Vent near the breaft. 
Gadus. - - - Peftoral fins tapering to a point, 
Blennius. - - Ventral fins of two united rays. 
Kurtus. - - Back elevated, 
III. Thoracici. The charafters of this order are, bony 
rays to the gills ; ventral fins direftly under the peftorals. 
This is the mod: confiderable order, containing twenty- 
four genera: 
Cepola. - - - Body endform, no viiible fcales. 
Gymnetrus. - Anal fin none. 
Echeneis. - - Back of the head fiat, tranfverfely fur¬ 
rowed. 
Coryphaena. - Head doping fuddenly downwards. 
Gobius. - - Ventral fins united into an oval fin. 
Cottus. - - Head broader than the body. 
Scorpasna. - Head armed with prickles. 
Zeus. - Upper lip arched by a tranfverfe mem¬ 
brane. 
Pleuroneftes. - Eyes both on one fide of the head. 
Chsetodon. - - Teeth fetaceous, flexile, crowded. 
Sparus. - - Teeth ftrong, obtufe; lips double. 
Bodianus. - - Opercula not ferrated, but armed with 
fcales and fpines. 
Holocentrus. - Opercula ferrated, and armed with fcales 
and fpines. 
Lutjanus. - - Opercula fcaly, ferrated, but not armed 
with fpines. 
Scarus. - - Teeth none; jaws crenate at the edges. 
Labrus. - - Dorfal fin with a dender Ikin beyond 
the end of each Tay. 
Sciaena. - - Head and gill-coverts with ftrongly 
fixed fcales. 
Perea. - - Gill-coverts three-leaved, the upper fer« 
rate. 
Gafterofteus. - Tail carinate at the fides. 
Scomber. - - Tail carinate at the fides; feveral fpu- 
rious fins between the dorfal fin and 
tail. 
Centrogafter. - Tail carinate at the fides; ventral fins 
connected by a membrane, the firlt 
four rays fpinous, the other fix un¬ 
armed. 
Mullus. - - Body and gill-coverts with large lax 
fcales. 
Trigla. - - - Diltinft appendages near the peftoral fins. . 
Ophicephalus. - Head flat, fcales of a varied fliape. 
IV. Aedominales. The charafters of this order are, 
bony rays to the gills; the ventral, fins farther back than 
the peftorals, but before the anal. This order contains 
feventeen genera: 
Cobitis. - - Body hardly decreafing toward* the tail,.. 
Arnia, - - - Head naked, bony, rough. 
Silurus. ■■ - Firft ray of the dorfal or peftoral fins 
toothed. 
Teuthis. - ~ Head truncate on the fore-part. 
Loricaria.: 
