viii - Contents 



17. The Circulatory System 318 



18. Absorption, Metabolism, and the Diet 339 



19. Respiration 357 



20. Excretion 369 



21. Reproduction in Multicellular Animals 380 



22. The Endocrine Glands 398 



23. Responses of Higher Animals: The Receptors 419 



24. Responses of Higher Animals: The Effectors 431 



25. Responses of Higher Animals: The Nervous System 447 



Part IV. HEREDITY AND EVOLUTION 



26. Heredity 475 



27. Genes: Nature and Mode of Action 520 



28. Natural Selection: Origin ot Species 538 



29. The Consequences ol Evolution 552 



30. Ecology and Evolution 573 



31. The Plant Kingdom 592 



32. The Animal Kingdom 624 



Appendix I — Classification of Organisms 679 



Appendix II — Glossary 685 



Index 699 



