xiv CONTENTS 



chapter page 



8. General Problems Related to Single-celled Animals 195 



Colonial Protozoa and the Comparison of Unicellular with Multi- 

 cellular Organisms 195 



Biogenesis vs. Abiogenesis 202 



Protozoa and Disease 206 



9. Reproduction 213 



The Reproductive Cycle 213 



Modes of Reproduction 219 



Processes Related to Sexual Reproduction in Metazoa 221 



10. Classification and General Organization of Animals 237 



Classification 237 



General Organization of the Animal Body 243 



11. The Hydra, A Simple Many-celled Animal 247 



The Hydra as a Simple Metazoan 247 



Other Coelenterata 274 



12. The Earthworm and Other Annulata 282 



The Earthworm 283 



Other Annulata 309 



13. The Animal Nervous System 315 



The Sensory-neuro-muscular System 316 



Forms of Behavior in Animals 318 



14. The Crayfish and the Arthropoda 321 



The Crayfish 321 



Other Crustacea 332 



The Phylum Arthropoda 338 



15. The Locust 342 



The Locust, or Short-horned Grasshopper 343 



16. Some Representative Insects 371 



Classification and General Organization 371 



Some Representative Insects ...._. 377 



17. Development op the Frog and Other Vertebrata 397 



Development of Amphioxus 398 



Development of the Leopard Frog 400 



Development of Other Vertebrates 420 



