TABLE OF CONTENTS XI 



PAGE 



cretion (171). Respiration (172). Sensations (172). Ner- 

 vous system (172). Reproduction (173). Economic impor- 

 tance (173)- Segmentation (174). Body cavity (174). 

 Leeches (175). Fresh-water segmented worms (176). Marine 

 segmented worms (176). Characteristics and classification 

 of the Annelida (177). 



CHAPTER XX 



THE ROUNDWORMS 178 



''Horsehair snakes" (178). Intestinal parasites (178). 

 Trichina (179). Hookworm (179). Elephantiasis (181). 

 Other roundworms (iSi). Characteristics and classification 

 (182). 



CHAPTER XXI 



THE FLATWORMS 183 



Planaria (183). Parasitic flatworms (185). The liver 

 fluke (186). The tapeworm (188). Characteristics and 

 classification (191). 



CHAPTER XXII 



THE ECHINODERMS , . . .192 



Symmetry (192). Starfishes (193). Brittlestars (195) 

 Sea urchins (196). Sea cucumbers (196). Sea lilies (197)- 



CHAPTER XXIII 

 THE CGELENTERATES ... 198 



Hydra (199)- Digestion ^203). Reproduction (203). 



Regeneration (204). Division of labor among individuals of 



a colony (204). Alternation of generations (205). Jellyfish 



(207). Sea anemones (207). Coral (208). Characteristics 



and classification (210). 



CHAPTER XXIV 

 THE SPONGES 211 



A simple sponge (211). Reproduction (212). Grantia 

 (213). Flow of water in fresh-water sponge (214). Spicules 

 and spongin (215). The relations of sponges to other 

 organisms and toman (215). Characteristics and classifica- 

 tions (217). 



