Abstract
Tritiated thymidine was administered at various times, and for various lengths of time, during the larval stages of
Drosophila melanogaster. The thymidine was incorporated into DNA and was subsequently detected by autoradiography. These procedures allowed identification of those cells undergoing DNA replication at a particular time and also allowed determination of subsequent changes in relative position of these cells and some of their progeny. An analysis of these data has elucidated characteristic patterns of cell division and cell movement in the formation of the adult nervous system during postembryonic developmental stages.