20 INTRODUCTION. 



3. Reptiles. 



4. Fishes. 



The class of MAMMALS is subdivided into three orders : 



a. Beasts of prey, (Carnivora.) 



b. Those which feed on vegetables, (Herbivora.) 



c. Animals of the whale kind, (Cetaceans.) 



The class of BIRDS is divided into four orders, namely, 



a. Perching Birds, (Insessores.) 



b. Climbers, (Scansores.) 



c. Waders, (Grallatores.) 



d. Swimmers, (Natatores.) 



The class of REPTILES is divided into five orders : 



a. Large reptiles with hollow teeth, most of which are 

 now extinct, (Rhizodonts.) 



fr. Lizards, (Lacertians.) 



c. Snakes, (Ophidians.) 



d. Turtles, (Chelonians.) 



e. Frogs and Salamanders, (BatracJiians.) 



The class of FISHES is divided into four orders : 



a. Those with enamelled scales, like the gar-pike, 



(Ganoids,) fig. 157, c. 



b. Those with the skin like shagreen, as the sharks and 



skates, (Placoids.) 



c. Those which have the edge of the scales toothed, 



and usually with some bony rays to the fins, as the 

 perch, (Ctenoids.) 



