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CHAPTER XxX. 
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 
blue, green, red, and black. 
Fishes are essentially 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 pectoral fins. The posterior limbs occupy 
the lower surface of the body, and form the ventral 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, cdd 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 (4ydrargyra) ; and 
the Ferca scandens, which in Tranquebar not merely walks over level ground, but 
climbs trees. 
