o working hypothesis amounts to much until it has been tested on
suitable material. Indeed, the choice of an appropriate experimental
system has often been the key to the solution of a problem. The present
volume is devoted to insect imaginal disks. These groups of larval cells
are the primordia of precisely characterized adult counterparts, without
apparent function in larvae. At the onset of metamorphosis, the subtle
interplay of hormonal signals brings growth to a halt, and
differentiation begins. In the fruitfly, a host of mutations are known
to affect the development of disks; these provide ample material for
analysis. It was largely ERNST HADORN'S ingenuity that directed the
attention of many scientists around the world to this promising
experimental system, and to him this volume is dedicated. All the
contributors have been associated with him at one time or another, as
graduate students, postdoctoral fellows, or colleagues. Each author has
attempted to cover comprehensively the topic assigned to him. This has
inevitably led to some overlapping, for which the editors should be
blamed, not the authors, as this results from the way the topic was
subdivided at the outset. We believe this volume will be a welcome
sourcebook for the specialist in the field, and a provocative monograph
for the uninitiated scientist interested in the exciting area of cell
determination.