FISHES. 
IN the FISHES, the last class of vertebrated animals, the chief and mosi 
obvious distinction lies in their adaptation to a sub-aqueous existence, and 
their unfitness for life upon dry land. Carte 
‘There are many vertebrate animals which pass the whole of their lives in 
the water, and would die if transferred to the land, such as the whales and 
the whole of the cetacean tribe, an account of which may be found in page 
127. But these creatures are generally incapable of passing their life beneath 
the waters, as their lungs are tormed like those of the mammalia, and they 
are forced to breathe atmospheric air at the surface of the waves. And 
though they would die if left upon land, their death would occur from 
inability to move about in search of focd, and in almost every case a 
submersion of two continuous hours would drown the longest breathed whale 
that swims the seas. . . 
The Fishes, on the contrary, are expressly formed for aquatic existence ; 
and the beautiful respiratory organs, which we know by the popular term of 
“gills,” are so constructed that they can supply sufficient oxygen for the 
aération of the blood. 
The reason that Fishes die when removed from the water is not because 
the air is poisonous to them, as some seem to fancy, but because the delicate 
gill-membranes become dry and collapse against each other, so that the cir- 
culation of the blood is stopped, and the oxygen of the atmosphere can no 
longer act upon it. It necessarily follows, that those Fishes whose gills can 
longest retain moisture will live longest on dry land, and that those whose 
gills dry most rapidly will die the soonest. The herring, for example, where 
the delicate membranes are not sufficiently guarded from the effects of heat 
and evaporation, dies almost immediately it is taken out of the water ; 
whereas the carp, a fish whose gill-covers can retain much moisture, will 
survive for an astonishingly long time upon dry land; and the anabas, or 
climbing perch, is actually able to travel from one pool to another, ascending 
the banks, and even traversing hot and dusty roads. 
~The power by which the Fishes propel themselves through the water is 
almost entirely obtained by the lateral movement of the tail. The fins are 
scarcely employed at all in progression, but are usually used as balancers, and 
occasionally to check an onward movement. 
Before proceeding further, I may mention that all the fins of a Fish are 
distinguished by appropriate names. As they are extremely important in 
determining the species and even the genus of the individual, and as these 
members will be repeatedly mentioned in the following pages, I will briefly 
describe them. 
Beginning at the head and following the line of the back, we come upon a 
fin, called from its position the “dorsal” fin. In very many species there are 
two such fins, called, from their relative positions, the first and the second 
dorsal fins. The extremity of the body is furnished with another fin, 
popularly called the tail, but inore correctly the “caudal” fin. The fins which 
are set on that part of the body which corresponds to the shoulders are 
termed the “ pectoral” fins ; that which is found on the under surface and in 
front of the vent is called the “abdominal” fin, and that which is also on the 
lower surface, and between the vent and tail, is known by the name of the 
“anal” fin. All these fins vary extremely in shape, size, and even in position. 
. The gill-cover, or operculum as it is technically called, is separated into 
four portions, and is so extensively used in determining the genus and species, 
