xxii INTRODUCTION 



Insects — Body in segments, reproduce by a complete change in form. 



Crustaceans (Crabs, Lobsters, etc.) — Skeleton external; gill-breathing, 

 chiefly aquatic. 



MoLLUsKs ("Shell-Fish") — Soft-bodied, usually covered by a hard, limy 

 shell. 



Worms — True worms, and other forms not fitting in elsewhere. 



Star-Fishes — Salt-water animals, with star-like structure. 



Corals — Minute, salt-water animals, which build up solid masses of their 

 limy skeletons. 



Jelly-Fishes — Disk-shaped, jelly-like sea animals, with no hard parts. 



Sponges — Stationary aquatic animals, which look like plants; skeletons of 

 tough, fibrous cells. 



Protozoans — Lowest forms of life, beginning with the single cell; mostly 

 microscopic. 



HOW ANIMALS ARE CLASSIFIED 



In order to know and appreciate even a small proportion of the 

 world's animals, their correct arrangement into groups is as neces- 

 sary as a systematic arrangement of the books in a vast library. 

 By their forms and characters, animals are divided into natural 

 groups and subdivisions, and in order that we may understand 

 their proper relationships, and their places in Nature, we must learn 

 and remember the general principles of animal classification. 

 Without this foundation knowledge, a clear view of the splendid 

 domain of animal life is impossible, and the life histories of our 

 living creatures will be but a jumble of disconnected facts of very 

 slight practical use. 



When properly simplified, the classification of the principal 

 groups of our vertebrate animals is as easily learned and remem- 

 bered as the leading facts of geography. Once learned, each animal 

 observed thereafter can be located in the group to which it belongs, 

 and its place in Nature understood. This helps toward exact 

 knowledge of its anatomy and habits. 



