FISH AND FISHERIES. 5 
from passing over the gills. The above account will generally describe 
the gills of Teleosteans, The sharks and rays have a different arrange- 
ment. There are certain other fishes in which the gills are so peculiar, 
such as some Siluride, Labyrinthici, &., that larger works on Ichthyology 
must be consulted concerning them. 
Another organ to which attention must be paid is the air-bladder. 
This is a hollow sac of very varying shape. It is situated in the abdo- 
men, but not within the same sac with the intestines. It is either entirely 
closed or communicates by a duct with the latter. It is full of gas, not 
air, and curiously enough the nature of the gas differs in fresh-water 
fishes and those of the ocean. In the former case the gas is principally 
nitrogen ; in the latter, especially in deep-sea fishes, it is oxygen which 
predominates. In some fishes the air-bladder assumes the character of a 
lung ; in the Leptocardii, Cyclostomi, Chondropterygit and . Holocephali, 
it is wanting : in the others its office is supposed to be useful in altering 
by compression the specific gravity, and either to change the fish’s centre 
of gravity or enable it to sink and float at will. 
The shape of the intestinal tract in fishes is subject to all sorts of 
variations, Asa rule it is shorter in carnivorous fishes and longer in 
vegetable feeders. It is often uniform throughout, so that the different 
portions of stomach, esophagus, intestine, and rectum cannot be distin- 
guished. But this is rarely the case in Teleosteans. There are two 
forms of stomach common. One is the siphonal, in which the organ is 
bent intotwo portions ; the other is the cecal, in which one end is prolonged 
into a long descending blind sac. Besides this there are commonly 
among Teleosteans a number of hollow worm-like appendages, varying 
in numbers in different species from two or three to 200; they open 
into the intestine at the pyloric* orifice of the stomach, and are called 
pyloric appendages. They are much used as distinguishing marks 
between one species and another. 
Fishes have liver, spleen, pancreas, and intestines variously modified. 
The liver is mainly distinguished for the quantity of oil which it con- 
tains. Details about these organs are not within the purpose of this 
work; they are, however, of especial interest to those who wish to 
pursue the subject. Gtinther’s work on the “Study of Fishes” is 
recommended for the purpose. What has been already given will be 
sufficient for all the purposes of classification.+ Ifany intelligent fisherman 
will take one of the fishes daily met with and examine it so as to see for 
himself the organs here referred to, he will learn practically what he is 
taught by reading, and it will effectually be impressed upon his mind. 
The skeleton next claims our attention, as it forms a great mark of 
distin¢tion between the two great sub-classes, Teleosteans and Sharks, é&c. 
The latter were called Chondropterygians, on account of the exclusively 
cartilaginous character of their bones. But there is great diversity in 
this, for while some have scarcely a consolidated cartilage, others present 
almost every degree of ossification. In some the vetebre can be hard] 
distinguished from one another, in others they are well defined and 
* Greek—Pule, a gate—the lower opening of the stomach leading to the intestines. 
+ Those who require the meanings of such terms as pancreas, spleen, &c., or the 
nature of the organs themselves, can learn all from the shilling manuals of physi- 
ology, published by M‘Millan, Collins, and others. 
