﻿xiv CONTENTS. 



CHAPTER XX. 



PAGE 



Worms . . . . . . . . . l5o 



Angle Worms, 154 • How they move, 154, 155 ; Leech, 155 ; Sea- Worms, 156, 157 ; 

 Tube-building Worms, 159. 



CHAPTER XXI. 

 Concerning Natural Groups . . . . . .160 



Characters of Articulates, 160 ; Of Worms and Mollusks, 161 ; Type Characters, 161 ; 

 Typical Animals, 162 ; Systematic Tables and Classification, 163. 



CHAPTER XXII. 



Characters op Vertebrates . . . . . .163 



External Characters of Salamanders, 163, 164; Comparison with Cat, 165; Differ- 

 ences between the two, 166; Young Salamander, 166; Skeleton of Cut, 167; 

 Vertebral Column and Spinal Cord, 169, 170; Bones of the Ankle and Wrist, 

 171, 172; Groups of Vertebrates, 173, 174. 



CHAPTER XXIII. 



Bones of the Leg and Wing op Birds . . . . .174 



Importance of studying Young Forms, 174; Wing Bones of an Adult Bird. 175; 

 Embryo Birds, and Wing Bones of same, 176; Leg Bones of an Adult Bird, 

 177; Leg Bones of Embryo Bird, 178; Leg Bones of Young Toad, 180. 



CHAPTER XXIV. 



Classes and Sub-Kingdoms . . . . . .181 



Sub-Kingdom Mollusca, Class Gasteropoda, 181; Class Acephala, 182 ; Sub-King- 

 dom Arthropoda, Class Insecta, 183 ; Class Myriopoda, 184 ; Class Arachnida, 

 185 ; Sub-Kingdom Vermes, Class Annelida, 185 ; Class Crustacea, 186 ; Sub- 

 Kingdom Vertebrata, 187. 



Notice to Teachers ....... 189 



