THE SHORES OF BRITAIN. 67 



their simplicity of figure, the absence of those pro- 

 minent limbs which project from the bodies of most 

 other vertebrate animals ; the head, without any 

 visible neck, merging into the rounded body, which 

 terminates in the tail in an almost unbroken outline, 

 for the fi.ns are usually so slight and membranous in 

 their texture as scarcely to diminish this unity of 

 form. The smooth and glittering armour in which 

 these animals are for the most part invested, tends to 

 tlie same end. Feathers or fur would greatly impede 

 progress through water ; and as the tribes of fishes 

 are what is commonly called cold-blooded, or of 

 nearly the same temperature as the fluid that sur- 

 rounds them, those non-conductors of heat would be 

 of no service, the animal heat necessary for existence 

 not being liable to be abstracted. In place of those 

 clothing substances, the fish's body is encased in a 

 coat of mail formed of many pieces of similar shape, 

 of a transparent horny substance, which are imbedded 

 in the skin on the side next the head, and overlap 

 the succeeding ones at the posterior edge, like the 

 tiles of a house. It is obvious how beautifully and 

 effectually this formation precludes any impediment 

 in swimming, arising from the free edges of the scales. 

 These are so closely pressed on each other, that the 

 water cannot penetrate, and are covered, moreover, 

 in many fishes, with a glutinous slime, which water 

 does not dissolve. The scales of fishes afford objects 

 of very beautiful structure when viewed with a 

 microscope. They are various in their form ; those 

 from different parts of the body not being quite alilce 

 even in the same fish. They are not perfectly flat, 



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