18 Smaller Ecdysozoans 19 Trilobites, Chelicerates, and Myriapods 20 Crustaceans 21 Hexapods 22 Echinoderms, and Hemichordates 23 Chordates 24 Fishes 25 Early Tetrapods and Modern Amphibians 26 Amniote Origins and Nonavian Reptiles 27 Birds 28 Mammals PART FOUR Activity of Life 29 Support, Protection, and Movement 30 Homeostasis: Osmotic Regulation, Excretion, and Temperature Regulation 31 Homeostasis: Internal Fluids and Respiration 32 Digestion and Nutrition 33 Nervous Coordination: Nervous System and Sense Organs 34 Chemical Coordination: Endocrine System 35 Immunity 36 Animal Behavior PART FIVE Animals and Their Environments 37 Animal Distributions 38 Animal Ecology