Mitotic pattern in the different histoblast nests, and the temporal sequence of fusion and differentiation of these nests and spiracular anlagen resulting in the formation of the different regions of the adult abdomen of Drosophila melanogaster were studied by examining whole mount preparations and histological sections of the epidermis from closely timed developmental stages. The relationship between the boundaries of the primary (larval) and secondary (adult) segments was determined by following the points of insertion of the dorsal internal oblique muscles which persist through metamorphosis. These studies indicate that the descendants of the anterior dorsal histoblast nest form the hairy and bristled region of the tergum, while those of the anterior and posterior groups of the posterior dorsal nest give rise to the intersegmental membrane and acrotergite respectively; the ventral histoblast cells give rise to the sternum and pleural region while the spiracular anlage forms the spiracle. These findings confirm and extend the conclusions derived from genetic analysis or after experimental inductions of defects, on the lineage of the various histoblast nests.