CONTENTS xi 



CHAPTER XIV 



PAGE 



HYDRA AND ITS ALLIES ......... 205 



APPENDICES : Key to the principal subdivisions of the Cnidaria 220 



Key to the families of the Hydromedusae .... 220 



CHAPTER XV 



THE PARAMECIUM AND ITS ALLIES 222 



APPENDICES : Key to the four classes of Protozoa . . . 229 



Key to the subclasses and orders of Infusoria . . . 229 



CHAPTER XVI 



THE SMELT AND ITS ALLIES ........ 230 



APPENDICES : Key to the principal orders of fishes . . . 252 



Key to the six suborders of Teleostei 252 



CHAPTER XVII 



THE NEWT AND ITS ALLIES ........ 254 



APPENDICES : Key to the orders of Amphibia .... 266 



Key to the families of Urodela 266 



CHAPTER XVIII 



THE LIZARD AND ITS ALLIES 268 



APPENDIX : Key to the four orders of Reptiles .... 280 



CHAPTER XIX 



THE ENGLISH SPARROW AND ITS ALLIES 281 



APPENDICES : Key to the orders of Birds 314 



Key to the families of Passeres of northern United States . 315 



CHAPTER XX 



THE MOUSE AND ITS ALLIES 318 



APPENDIX : Key to the orders of Mammalia .... 331 



CHAPTER XXI 



THE DEVELOPMENT OF THE FROG'S EGG . . . 332 



