Assessment of the state of current knowledge in the field and an attempt to identify future avenues of research. After a brief historical overview, which identifies the conceptual underpinnings of twentieth-century invertebrate zoology and embryology, the book is organized by developmental stages. The authors first present chapters on oogenesis, spermatogenesis, fertilization, and embryonic development. A subsequent section - arranged phylogenetically to encompass annelids, priapulans, molluscs, bryozoans, and echinoderms - covers larval morphology and evolution. The final section treats larval or adult populations and includes new information on the role of hyrodynamics to aid in the understanding of larval dispersal and settlement.