502 THE OCEAN WORLD. 



CHAPTEK XVIII. 



FISHES. 



BEFORE speaking of the habits of the principal kinds of fishes, it is 

 desirable to glance at their organization, and upon the manner in 

 which they execute their physiological functions. 



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

 has impressed its seal upon their organization. Nevertheless, their 

 forms are very varied ; they are generally oblong, 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, 

 generally a thin bony substance 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, from golden or 

 silver, and other dazzling colours, mingling with shades of blue, green, 

 red, and black. 



Fishes are essentially formed for swimming (Fig. 340), and all their 

 members are adapted for this purpose. The anterior members, 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 members occupy the lower surface of the 

 body, and form the ventral fins. The latter, which are always over 

 the ventral line, may be before, beneath, or behind the former. Fishes 

 possess, besides, fins in odd numbers. The fins which erect themselves 

 on the back are called the back or dorsal fins, those at the end of the 

 tail are the caudal fins ; finally, there is frequently another attached 



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

 marches 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. 



