362 ABOUT THE FISHES. 



According to Sching, there are 7 tortoises, 33 serpents, and 

 35 lizards. 



Fishes are the least known of those superior animals whose 

 skeleton and vertebral column are situated in the interior of 

 the body, and which are thence named Vertebrata. The richest 

 collections, such as those of the British Museum, and those 

 of the Museum of Natural History in -Paris, which contain 

 about 3000 species, do not represent probably more than a 

 fourth of the existing total, including fresh-water and salt- 

 water fish. How many rivers and streams in both hemi- 

 spheres still remain to be explored ! How far we are from a 

 knowledge of the fishes which people the different strata of the 

 great ocean. 



Agassiz divides this great class of vertebrated animals into 

 the four orders of Cycloid, Ctenoid, Placoid, and Ganoid, accord- 

 ing to the character of their scales. Cuvier, into Osseous 

 fishes (with true bones), and Cartilaginous ; subdividing the 

 former into Acanthopterygii and Malacopterygii. 



The difficulty of the problem we are here considering in- 

 creases when we come to the inferior animals. Who would 

 pretend to determine the number of species of Mollusca which 

 inhabit the earth, the fresh waters and the salt ? This much is 

 certain, that it cannot be less than that of the Vertebrates. 



In the vast aggregate of the Articulata, the inquirer finds 

 himself utterly astray and bewildered. This great division 



