JSTRUCTUKE OF THE UlLLb. 191 



regularity of structure, such as no human mosaic could ever 

 equal. 



Many of our European fishes are richly decorated with vivid 

 colours, but their scaly raiment is generally far from equalling 

 the gorgeous magnificence of the fishes of the tropical seas. 



If in the birds of the equatorial zone a part of the plumage 

 sparkles with a gem-like brilliancy, all the colours of the rain- 

 bow combine to decorate the raiment of the tropical fishes, and 

 no human art can reproduce the beauty of their metallic lustre, 

 which at every movement in the crystalline waters exhibits to 

 the enchanted eye new combinations and reflections of the 

 most splendid tints. 



The gaudiest fishes live among the coral reefs. In the tepid 

 waters, where the zoophytes, those sensitive flowers of the ocean, 

 build their submarine palaces, we find the brilliant Chetodons, 

 the gorgeous Balistinaa, and the azure Grlyphysodons gliding 

 from coral branch to coral branch like the playful Colibris, that 

 over the Brazilian fields dart from one lustrous petal to another. 



Oxygen is as necessary to fishes and other marine creatures as 

 it is to the terrestrial animals, but as they are obliged to draw 

 it from a denser element, which absorbs but a small volume of 

 air, their gills are necessarily differently constructed from the 

 lungs of the creatures breathing in the atmosphere. In most 

 species, comprising all the bony fishes, and the sturgeons, 

 among those which have a cartilaginous skeleton, we find on 

 either side of the throat five apertures, separated from each 

 other by four crooked, parallel and unequal bones, and leading 

 to a cavity, which is closed on the outside by an operculum or 

 cover. In this cavity, and attached to the bones, are situated the 

 delicate membranes, bearded like feathers, which serve to aerate 

 the blood. The water constantly flows through the gills in one 

 direction, entering by the branchial apertures of the throat, and 

 emerging through the operculum. This is, in more than one 

 respect, a most wise provision of Nature ; for if the fishes were 

 obliged to receive and reject the water by the same aperture, 

 as we do the air, each expiration would evidently drive them 

 backwards, and consequently retard their movements. It is 

 also evident that the delicate fringes or folds of the gills would 

 soon get into disorder if the water were carried through them in 

 two opposite directions. 



