Neurogenesis in Grasshopper and fushi tarazu Drosophila Embryos

Neurogenesis n insect embryos begins shortly after gastrulation as an undifferentiated two-dimensional epithelial sheet is transformed into a highly differen-tiated three-dimensional central nervous ystem (CNS). Here we discuss our studies aimed at understanding the mechanisms underlying this early phase of neuronal development during which time hundreds of neurons are born in each segmental neuromere and acquire their individual determination. During the next phase of de-velopment, each of these neurons begins to express its unique specificity as it extends a process, called a growth cone, which finds and recognizes its appropri-ate targets (e.g., Goodman et al. 1984; Bastiani et al. 1985). The generation of the stereotyped pattern of identi-