STONE-SUCKERS, 
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few In number^ about fourteen species being the 
whole of those known to naturalists. They are 
found both in fresh and salt waters, principally 
in the northern parts of the world. Six of the 
number are enumerated as British, 
Genus Petromyzon, (Linn.) 
The Lampreys have a smooth, elongated, 
cylindrical body like that of an Eel. There are 
seven gill-apertures on each side ; the mouth is 
circular, and its inner surface is studded with 
hard, crusted tubercles, answering the purpose 
of teeth. The tongue, which moves backwards 
and forwards like a piston, has two rows of 
small teeth. The skin, elevated in a fold around 
the extremity of the body, answers to dorsal, 
caudal, and anal fins. 
The generic name applied to these fishes, 
Petromyzon, signifies Stone-sucker; and refers 
to a curious habit depending on the structure 
of the mouth. The animal applying its circular 
lip to the surface of a stone or other solid body 
in the water, draws in the piston-like tongue ; 
a vacuum is thus produced in the mouth, while 
the pressure of the super-incumbent body of 
water causes the lip to adhere to the stone with 
immense tenacity, until by the protrusion of the 
tongue the vacuum is voluntarily destroyed. 
It is supposed that the Lamprey resorts to 
this singular expedient to prevent its being con- 
stantly carried down by the current of the rivers 
in which it lives ; its powers of locomotion being 
feeble. But Sir William Jardine has shown that 
a much more obvious end is effected by the same 
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