SKELETON OF FISHES. 3 



they present the aspect of very thin laminae or plates, arranged in 

 the manner of tiles upon a roof, and held together in the folds 

 of the skin. "We may compare them to our nails ; but they 

 contain a much larger quantity of calcareous salts. The colours 

 with which these animals are adorned, astonish us by their 

 variety and splendour. Sometimes they can only be compared 

 to the most brilliant gold and silver ; sometimes these present 

 tints of the richest green, blue, red, or the deepest black. The 

 silvery matter, which frequently gives to them so beautiful a 

 metallic splendour, is secreted by the skin, and is composed of a 

 number of small polished laminae. 



519. The Skeleton of Fishes is usually bony; but amongst 

 several of these animals, such as the Ray and the Shark, it re- 

 mains permanently in a fibre-cartilaginous or cartilaginous state; 

 and there are even some in which this frame- work possesses still 

 less solidity, and remains perfectly membranous : certain Lam- 

 preys are in this condition ; and in this manner they form a 



transition between the Vertebrated and Invertebrated animals. 



The bones never have any medullary canal ; and the cartilage 

 which constitutes their foundation is not the same as that of the 

 Mammalia and Birds ; for, when boiled in water, it does not 

 give out any gelatine. 



520. The skeleton is composed of the head, to which is 



FIG. 246 SKELETON OF THE PERTH. 



joined a highly-developed apparatus which is subservient to 



2 



