TUNNIES AND THEIR RELATIONS 



is thus reduced to a minimum. The conical, pointed 

 head is shaped like a fuse cap. The paired, or pectoral 

 and pelvic fins, which might be an obstacle, are 

 situated close to hollows in which they lie without 

 projecting beyond the surface of the trunk, when the 

 fish is swimming at full speed. When so swimming 

 the tunny is like a spindle of polished steel, made in 

 such a way that it does not present the slightest 

 roughness of surface. Only the median fins project, 

 the caudal fin behind aiding the forward movement, 

 while the dorsal fins above and the anal fin below 

 help to preserve the equilibrium by preventing the 

 body rolling sideways in the water. 



The main propeller is at the rear like the screw of 

 a ship; it is not lateral. The pectoral fins, though 

 they appear to do so, play no part when the fish is 

 swimming rapidly; they lie out of the way in their 

 hollow when the body is moving at full speed. In 

 the earliest days of steam navigation paddle steamers 

 had wheels at the side. To-day they are only used in 

 special cases to facilitate handling and landing when 

 there is little depth of water. The paddle-wheels 

 have been replaced by screws submerged at the stern 

 of the ship, and these propellers are less cumbersome, 

 possessed of greater force and greater efficiency. 

 Nature acts in an exactly similar manner. Fishes 

 have their propeller behind them, namely the tail 

 with its caudal fin which acts as a scull to strike the 

 water. 



The tail-fin of the tunnies takes the form of an 

 upright blade which is full and sharp, curved in the 

 form of a crescent, almost as high as, or even higher 

 than, the body is thick. Made of two equal halves, 

 one above the other, both are firmly attached at the 

 hinder end of the body to the deep compressed 

 caudal portion which terminates the trunk; and their 

 rays, rigid and strong, have the firmness and solidity 

 which their use demands. When we look at and 

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