Vlll CONTENTS 



Part V. EVOLUTION OF ANIMALS 



21. The Protozoans — Representatives of Unicellular Animals 425 



22. Sponges — A Side Line of Evolution 454 



23. Coelenterates — Simple Multicellular Animals 465 



24. Ctenophores — Comb Jellies or Sea Walnuts 493 



25. Flatworms — Vanguard of the Higher Animals 498 



26. Roundworms — The Tubular Plan 519 



27. An Aquatic Miscellany 533 



28. Annelids — Pioneers in Segmentation 552 



29. Arthropods — Crustaceans 572 



30. Arthropods — Insects, Spiders, and Allies 589 



31. MoUusks — Specialists in Security 630 



32. Echinoderms — Forerunners of the Vertebrates 651 



33. Introduction to the Vertebrates — Lower Chordates and Fishes . . 662 



34. Amphibians — The Frog, An Example of the Vertebrates 681 



35. Reptiles — First Land Vertebrates 713 



36. Birds — Conquest of the Air 729 



37. Mammals and Mankind 752 



Part VI. EVOLUTION AND CONSERVATION 



38. Organic Evolution — Conservation 777 



Appendix 795 



Scheme of Classification 795 



The Plant Kingdom 795 



The Animal Kingdom 796 



Equivalent Measurements 799 



Suggested Reading 801 



Index 819 



