136 



ZOOLOGY. 



Reptiles 



3000 



'Amphibians 



700 



Arachnida 



4.000 



Molluskfi 



Tunicata, etc. { 25000 



400, 



Crustacea 



6000 



rrtj , Trr I200 



Ihread Pf^orms 



Flat Worms 

 1700 



Annelids /Molluscoidea 



Coelenterates 



Protozoa 



4000 



FIG. 64. Diagram showing the general relations of the chief divisions of the animal 

 kingdom. The number of species belonging to each is roughly approximate, only. 



172. Reptiles. This is a class recognized by zoologists 

 which is not nearly so easy to define or to identify as either of 

 the preceding. This is partly because the animals composing 

 it differ more among themselves than in the other classes. It 



