Class Pisces (Fishes 
Fishes are Vertebrate Animals with cold red | a large quantity of blood. 
blood, living in water, and breathing by gills or 
branchie. The 
The body is generally scaly; in some 
instances it is covered with plates, but is very rarely 
naked. They move by 
bony rays connected by 
horizontal, or paired (i. 
each side of the body), 
paired. 
heart has one auricle and one 
ventricle. 
means of fins, which are 
skin. The fins are partly 
e. placed symmetrically on 
and partly vertical, or un- 
The former are divided into pectoral 
ventral fins, and the latter into dorsal, anal, 
caudal, according to their position. The pectoral 
and ventral fins represent the fore and hinder ex- 
tremities of the higher Vertebrata. The fins are 
divided according to their structure, into spinous 
fins, consisting of stiff unjointed rays; soft fins, con- 
sisting of jointed and sometimes branched rays, and 
fatty fins, unsupported by rays. 
principal organ of locomotion. 
Most fishes, but 
all 
curious 
and 
and 
The tail-fin is the 
not 7) possess a 
air - bladder, 
consisting of a hollow 
sac filled with gas, 
which is connected in 
some species with the 
auditory organs, and 
MD 
x 
SS 
(uy 
\ 
Wi apg 
RAN 
XS 

They are either situated 
a gill-cavity into which the water can penetrate 
through the gill-opening, which is closed by the gill- 
in 
cover, and are then called internal gills, or in a few 
exceptional cases, they also project from the surface 
of the body into the surrounding water; and are 
then called external gills. Water, 
air and oxygen, is taken in through the mouth, and 
which contains 
when the mouth is closed, it passes into the gills, 
which lie on each side behind the head; and is after- 
The 
fish can only breathe with its gills as long as they 
wards discharged through the gill-openings. 
remain moist, as when they grow dry, the layers 
adhere together, and the blood can no longer circu- 
late through them. 
Different species of fishes inhabit salt and fresh 
water; and some can live in either. They are believed 

to be more numerous on the coasts than in open water. 
Most fishes are oviparous, but the number of 
“eggs which they lay is 
very variable. In the 
herring the roes con- 
tain 30,000 to 40,000 
eggs; in the carp 
700,000, in the stur- 
geon 1,400,000, and in 
the cod 
as many as 
in others with those 13,000,000. Neverthe- 
of digestion. By its less the number of 
compression or ex- é fishes tends rather to 
P i Skeleton of Perch. Bee. | . 
pansion the fish 1S a Anterior dorsal fin, b. Posterior dorsal fin, e¢, Caudal fin, d. Anal fin. diminish than to in- 
enabled to rise or sink e Ventral fin, f. Pectoral Fin. crease, on account of 
in the water. The form of fishes is generally rather | the number of othr animals which prey upon 
long, 
and laterally compressed. The head is small, 
and the neck is wanting. The skeleton is either bony, 
The 
often very small, unconnected with a breastbone, 
and only enclose abdominal organs. 
or else more or less cartilaginous. ribs are 
The organs of sense are not highly developed. 
The brain’ occupies a comparatively small 
tion of the cavity of the skull. The eye has 
usually no eyelids, a flat cornea, and a globular lens. 
The nostrils are only two blind cavities, and there 
are no external ears. The tongue is generally bony, 
and is often furnished with teeth. The teeth them- 
selves vary extremely in size and position, and are 
generally used to seize and hold prey; rarely for 
mastication. 
por- 
The breathing-organs, or gills, are thin, deli- 
cate and extremely porous layers, presenting a large 
surface in a small compass, so that they can contain 

them, including many species belonging to their 
own Class. 
In the spawning-season many fishes which usually 
inhabit the sea, enter rivers for that purpose; and 
others, like the Herring, gather together in enormous 
shoals, and approach the coasts in search of suitable 
places to deposite their ova, when they are captured 
in enormous numbers. 
Fish are extremely important as an article of 
food among all of 
c=) 
species are some of the large sharks &c., and a few 
races men. The only injurious 
smaller fishes, which are poisonous. 
As a rule, fishes are carnivorous animals, com- 
paratively few, such as the Carps, feeding chiefly on 
About 13,000 
known at present; and the small number which we 
vegetable substances. species are 
can find room to mention in the present work, may 
be 
arranged 
ged according to the following system ; 
