527 



CHAPTER XX. 



Fishes. 



Before speaking of the habits of the principal kinds of fishes, it 

 is desirable to glance very briefly at their organisation. 



Fishes are intended to live always* in water, and this circum- 

 stance has impressed its mark upon their organisation ; nevertheless, 

 their forms are very varied. They are generally oblong and compressed 

 laterally; they have no neck, the head being merely a prolongation 

 of the trunk. In the majority of instances, the body is covered with 

 scales, which may be described as thin bony substances, developed 

 out of the skin and over-lapping each other like the tiles of a roof. 



Nothing is more remarkable than the variety and brilliancy of 

 colour in fishes ; they present almost every gradation of colour, from 

 gold or silver, and other dazzling colours, to the loveliest tints of 

 l)lue, green, red, and black. 



Fishes are essencially formed for swimming (Fig. 348), and all 

 the different parts of their bodies are adapted for this purpose. The 

 anterior limbs, which correspond with the arms in man and the wings 

 in birds, are attached to each side of the trunk, immediately behind 

 the head, and form the pect07-al fins. The posterior limbs occupy 

 the lower surface of the body, and form the vetitral fins. The latter, 

 which are always over the ventral line, may be placed before, be- 

 neath, or, as is most usual, behind the former. Fishes possess, 

 besides these two pair of fins, odd fins. The fins which are found 

 on the back or dorsum are called the back or dorsal fins, those at 

 the end of the tail are the caudal fins ; finally, there is frequently 

 another attached to the lower extremity of the body, which is called 

 the anal fin. These fins are always nearly of the same structure, 



* The exceptions to these are the Doras, or flat-headed Hassars of India, which 

 march overland in large droves ; the Swampines of Carolina {Hydrargyra) ; and 

 the Perca scandens, which in Tranquebar not merely walks over level ground, but 

 climbs trees. 



