xii CONTENTS. 



CHAPTER XX. 



PAGE 

 WOEMS .... .... 153 



Angle "Worms, 154 ; How they move, 154, 155 ; Lcecli, 155 ; Sea- Worms, 156, 157 ; 

 Tube-building Worms, 159. 



CHAPTER XXI. 



Concerning Natural Groups ... .160 



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

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



CHAPTER XXII. 



ClIAEAOTERS 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, 167; 

 Vertebral Colninn 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 of Birds .... 1*74 



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 Mollusea, Class Gasteropoda, ISl; Class Acephala, 182; Sub-King- 

 dom Arthrnpoda, Class Insecta, 1S8 ; Cliiss Myriopoda, 184 ; Class Arachnida, 

 1^5; Sub-Kingdom Vermes, Class Annelida, iV.'i ; Class Crustacea, ISO ; Sub- 

 Kingdom Vertebrata, 1S7. 



Notice to Teachers . . . 189 



