In addition to exploring the organismal, cellular and molecular aspects of animal development, the 6th edition of "Developmental Biology" expands its coverage of both the environmental regulation of developmental and evolutionary biology. New features include full-color illustrations, references, indexes (subject, author and website) and chapter summaries. An associated website [http://zygote.swarthmore.edu/index.html] is cross-referenced throughout the text, providing more information for advanced students, historical, philosophical and ethical perspectives on issues in developmental biology, movies, interviews, web links and updates. There is an accompanying CD-ROM which takes the student through the developmental cycles of a number of the model organisms used in developmental biology and illustrates techniques used in studying these organisms. Features include over 130 interactive videos and 300 labeled photographs, study questions, web links and numerous "how to" sections giving instructions on experimental techniques.