STURGEONS. 



On the other hand, the scale of organization 

 descends to a lower point in the Cartilaginous 

 than any reached in the Osseous Orders. In the 

 extreme forms the skeleton becomes obsolete ; 

 the spine is no longer divided into vertehrcE, but 

 is reduced to a soft, flexible, transparent, and 

 slender column or thread of cartilage ; and the 

 animals can only with the utmost difficulty be 

 distinguished from Worms. 



Thus it seems probable that in a truly natural 

 arrangement, as the illustrious Cuvier has sug- 

 gested, the Cartilaginei ought not to be placed 

 either above or below other Fishes, but rather 

 as forming a parallel series, or Sub-Class, as the 

 Marsupialia form a series of Mammalia, paral- 

 lel with the Placentalia. 



The Cartilaginous Fishes are not very numer- 

 ous, when compared with the other Orders : they 

 are, however, widely scattered, some of them 

 being found in all seas, from the equator to the 

 seas surrounding either pole. They are almost 

 exclusively marine ; the Sturgeons and the Lam- 

 preys, however, are exceptions, inhabiting rivers. 

 Five Families are included in this Order, named, 

 respectively, Acipenseridce, Chimcsradcs, Squalidce, 

 Haiadce, and Petromyzofiidce, 



Family I. AciPENSERiDiE. 



(Sturgeons.) 



The Sturgeons have their gills free, like other 

 fishes, with a single opening, which is compa- 

 ratively wide, and protected by a large, oval, 

 radiated plate, as a gill-cover ; there are no gill- 



