This Third Edition of "Developmental Biology" is a fully updated and revised introduction to the phenomena of animal development. It provides a comprehensive account of the molecular and cellular concepts of development while placing them in the framework of the developing embryo. Many chapters have been extensively rewritten as the conceptual bases of these areas change. As might be expected, those chapters concerning embryonic induction, gene regulation, cell division, and pattern formation have changed enormously. In addition, a new chapter, "The Developmental Mechanics of Evolution", highlights the new research that links changes in development to evolutionary processes. While this book is designed for juniors and seniors, it does not assume more knowledge of biology than that provided by good introductory biology courses. Throughout, there are many boxes (Sidelights & Speculations) that highlight new work in the field, provide historical information, and detail the applicability of certain principles to other areas.