Many of the 14,000 genes of Drosophila are involved in the development of imaginal discs. These hollow sacs of cells make adult structures during metamorphosis, and their study is crucial to comprehending how a larva becomes a fully-functioning fly. This book examines the genetic circuitry of the well-known 'fruit fly', tackling questions of cell assemblage and pattern formation, of the hows and the whys behind the development of the fly. After an initial examination of the proximity versus pedigree imperatives, the book delves into bristle pattern formation and disc development, with entire chapters devoted to the leg, wing, and eye. Extensive appendices include a glossary of protein domains, catalogues of well-studied genes, and an outline of signaling pathways. More than 30 wiring diagrams among over 60 detailed schematics clarify the text. No student or practising scientist engaged in the study of Drosophila genetics should be without this comprehensive reference.