x iy CONTENTS. 



CHAPTER XX. 



PAGE 



WORMS ......... 153 



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 OF VERTEBRATES . . . . . .163 



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

 ences between the two, 166; Young Salamander, 166; Skeleton of Cat, 16T; 

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

 171, 172; Groups of Vertebrates, 178, 174. 



CHAPTER XXIII. 



BONES OP THE LEG AND WING OF 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 Insects, 183 ; Class Myriopoda, 184 ; Class Aracbnida, 

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

 Kingdom Vertebrata, 187. 



NOTICE TO TEACHERS . . . . .189 



