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 Siluridce, Lahyrinthici, &c., that lai'ger 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 difiers 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, Chondropterygii 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. As a rule it is shorter in carnivorous fishes and longer in 

 vegetable feeders. It is often uniform throughout, so that the difierent 

 portions of stomach, oesophagus, intestine, and rectum cannot be distin- 

 guished. But this is rarely the case iii Teleosteans. There are two 

 forms of stomach common. One is the siphonal, in which the organ is 

 bent into two portions; the other is the ccecal,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 purj)ose of this 

 work ; they are, however, of especial interest to those who wish to 

 pursue the subject. Giinther'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, f If any 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 

 distinction between the two great sub-classes, Teleosteans and Sharks, &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 vetebrse can be hardly 

 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. 



t 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. 



