Cell death during early morphogenesis: parallels between insect limb and vertebrate limb development.

The complex jointed leg of the adult fly is derived, in the pupal stage, from a simple lobed sac of cells. The gross morphological changes that result in adult shape are effected by a combination of differential cell growth and the programmed death of a large number of imaginal disc cells. Events are closely similar to those occurring in digit formation and limb contouring during vertebrate morphogenesis. In both cases phagocytic blood cells are intimately involved.