INTRODUCTION. Xlil 



Again, the warm-blooded animals are capable of being di- 

 vided into two classes. A part of them produce their young 

 alive, nourish them during infancy by their own milk from 

 organs called their mammae or breasts, and are hence called 

 Mammalia, or mammiferous animals. This class includes man, 

 quadrupeds, whales, porpoises, &c. Another part produce 

 their young by means of eggs, which they hatch by the heat 

 of their bodies, and support them by food, which they provide 

 for them as soon as they come out of the egg. This class 

 includes birds. 



The cold-blooded vertebrated animals also form two class- 

 es. The first contains those which breathe air only, and 

 cannot exist without it, as tortoises, frogs, serpents, &c. 

 These are called reptiles. The second contains those which 

 breathe by gills or branchiae, through the medium of the wa- 

 ter. This class includes all the true fishes, for the cetaceous 

 animals mentioned above are not properly to be numbered 

 among fishes. 



The invertebrated animals are not capable of so satisfac- 

 tory and accurate an arrangement. Their structure is not 

 yet sufficiently understood ; but they may be separated into 

 four divisions according to such circumstances of resem- 

 blance as the present state of knowledge with regard to them 

 admits. 



The whole animal world is thus arranged into two grand 

 kingdoms, and five distinct divisions. These are again sep- 

 arated into classes and subdivisions as in the following table. 



I. ANIMAMA VERTEBRATA. 



1. Division. VERTEBRATA. 



Class 1. Mammalia, J warm . blooded . 



2. Aves, ) 



3. Reptilia, | Gold . blooded . 



4. Pisces, ) 



II. ANIIHTALIA INVERTEBRATA. 



II. Division. HETEROGANGLIATA. 

 Class 1. Cephalopoda. Class 5. Tunicata. 



2. Pteropoda. 6. Brachiopoda. 



3. Gasteropoda. 7. Cirrhopoda. 



4. Conchifera. 



