FISH AND FISHERIES. 3 
present are fins, either in pairs along the sides or in a single line above 
and below. The skin is either (1) naked, (2) covered with scales, (3) 
with bony plates, (4) or bony armour. With few exceptions fishes 
propagate their species by means of eggs, and are hence called oviparous. 
Before proceeding to an explanation of the terms necessary to under- 
stand scientific books about fishes, it may be well to refer to a plan for 
their classification which is useful to remember. M. Louis Agassiz 
proposed to arrange all fishes into four great classes according to the 
structure of the scales or bony covering. Thus there were 1. PLacoips: 
Without proper scales, but instead plates of enamel either large or 
reduced to mere points: Sharks, Rays, &c. 2. Ganorps :—Scales 
angular, bony below, enamelled above. There are few living species of 
these, but there were many in former times. Our Australian Ceratodus 
is one, and the Sturgeon is another. 3. Crznorps :—Scales rough with 
comb-like teeth at their free margins, such as in Perch, Soles. 4. 
Cyciorps :—Scales smooth without teeth at the hind margin: Salmon, 
Mullet, Herring, Cod, &c. This classification is not adopted now, but it 
is found useful in many ways in determining the zoological character of 
a fish, and is moreover easily borne in mind. 
A more elaborate system of classification, and one generally adopted, 
is that of Giinther, which divides the class Fishes into four sub-classes. 
]. Patzicutuyes: Sharks, Ganoids, and Rays. 2. Tsxzoste1, which 
includes the majority of fishes. 3. Cycnostomata : Lampreys and a few 
other rare genera. 4. Leprocarpii. These divisions are more natural 
than any others, but they are founded on minute details of anatomy which 
require special knowledge to determine. Thus, PaL@ICcHTHYES are 
fishes with a contractile auricle to the heart ; intestine with a spiral 
valve ; optic nerves not crossing. 2. TELEosTEt :—Fishes with an auricle 
which does not contract, intestine not spiral, optic nerves not crossing. 
Skeleton composed of bone, with vertebre separated completely. 3. 
CycLostoma :—No auricle to the heart, intestine simple. Skeleton of 
cartilage instead of bone. Only one nasal aperture. No jaws, but the 
mouth surrounded by a circular lip. 4. Leprocarpi :—Heart reduced 
to mere pulsating sinuses in the great artery. Intestine simple. Skele- 
ton partly cartilaginous and partly membranaceous. No skull and no 
brain. 
We need not occupy ourselves with the two last orders, as CycLosto- 
MATA, or Lampreys and Myxines, only include five genera and not a 
dozen species, while the Lrprocarptl, or ,Lancelets, though distributed 
all over the world, have not more than two species. By many it is not 
considered a fish at all, but a separate class called Acranta, or headless. 
Thus according to this system there is little more than a division into 
—1. fishes with a skeleton of bone, and 2. fishes with a skeleton of 
cartilage. Before passing to the sub-divisions of these sub-classes it will 
be well to explain certain anatomical distinctions. Few fishermen will 
be able to trace them, but to understand them is easily effected and will 
give great insight into the physiology of fishes. 
All fishes (if we exclude the Lancelets) have red ‘blood, and are pro- 
vided with a complete circulation for the body, another for the gills, and 
a third for the liver. But fishes differ from other animals in this, that 
the heart is relatively small, and is provided with only two chambers, 
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