INTRODUCTION. XVII 



The class of INSECTS includes three orders. 



a. Those which have jaws for dividing their food 

 (Manducata) fig. 60. 



1}. Those with a trunk for sucking fluids, like the but- 

 terfly, (Suctoria] fig. 62 64. 



c. Those destitute of wings, like spiders, fleas (Apterd). 



The class CRUSTACEANS may be divided as follows : 



a. Those furnished with a shield like the crab and 



lobster (Malacostracd). 



b. Such as are not thus protected (Entomostraca). 



c. An extinct race, intermediate between these two 



(TriloUtes) fig. 156. 



The class of WORMS comprises three orders : 



a. Those which have thread-like gills about the head 



( Tubulibranchiates). 



b. Those whose gills are placed along the sides (Dor- 



sibranchiates). 



c. Those which have no exterior gills, like the earth- 



worm (Abranchiates). 



III. The department of MOLLUSKS is divided into three 

 classes, namely : 



1. Those which have arms about the mouth, like the 



cuttle-fish (Cepkalopods) fig. 47. 



2. Those which creep on a flattened disc or foot, like 



snails ( Gasteropods} fig. 88, 89. 



3. Those which have no distinct head, and are enclosed 



in a bivalve shell, like the clams (Aceplidls). 



The CEPHALOPODS may be divided into 



a. The cuttle-fishes, properly so called (Teuthideans), 



fig. 47. 



b. Those having a shell, divided by sinuous partitions 



into numerous chambers (Ammonites), fig. 164. 



