This text provides a comprehensive treatment of animal form, function, diversity and evolution. The principles of zoology are established in the first half of the book, and are then integrated into the later coverage of animal phyla. This edition includes a completely rewritten chapter on development, providing information on molecular development and historical information on nuclear transplantation experiments in addition to updated coverage of fertilization and activation, patterns of cleavage, gastrulation, mechanisms of development, mammalian development and pregnancy and birth. Organic evolution is presented from Aristotle to Darwinism to Neodarwinism, and focuses on the advent of evolution as a scientific theory.