CONTENTS 



PREFACE V 



Part I 

 ZOOLOGY AS A SCIENCE 



1. Zoology as a Science 3 



Part II 

 LIFE: ITS BEGINNINGS AND NATURE 



2. Early History of Life 21 



3. Units of Life — Cells 56 



Part III 

 THE ORGANIZED ANIMAL 



4. From Single Cells to Many Cells 65 



Part IV 

 THE RISE OF ANIMAL LIFE 



5. The Animal and Its Environment 87 



6. Orderliness among Animals 105 



7. Monocellular Animals — The Protozoa 108 



8. The Sponges and the Two-Layered Animals 136 



9. The Three-Layered Animals 160 



10. The Tube-within-a-Tube Body Plan 174 



11. Animals with Jointed Feet — The Arthropods 200 



12. Aberrant Animals — The Mollusks and Echinoderms 252 



13. The Animal Climax— The Chordates 278 



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