TABLE OF CONTENTS XI 



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

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

 tance (173). Segmentation (174). Body cavity (1 74) . 

 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 (181). 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 Ccelenterates . 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)- 



