Fig. 1.

Axon scaffold of the early embryonic brain of the grasshopper and Drosophila prior to central complex formation. a. Confocal image of the grasshopper brain at 43% of embryogenesis (e43%) following double-labeling with 8B7 (green) and DAPI (blue) reveals the commissural fascicles (white arrowheads) making up the primary brain commissure (com) crossing the median domain (MD) and linking both protocerebral (PC) hemispheres (dashed white outline). Bilateral anterior cell clusters (white asterisks) generate fiber tracts (open white arrowheads) to the commissural system. Some axons descend directly to more posterior neuromeres (deutocerebrum, tritocerebrum) and then into the ventral nerve cord (not shown). Arrow points to anterior (A) according to the neuraxis (n). b. Confocal image of the brain of Drosophila at E15 following labeling with BP106 (green) reveals fiber tracts (open white arrowheads) from progeny of neuroblasts (white asterisks) and contributing to fascicles (white arrowheads) of the primary brain commissure (com) linking both protocerebral (PC) hemispheres (dashed white outline). Arrow points to posterior (P) according to the body axis. Other abbreviations: mocnr, median ocellar nerve tract. Scale bar represents 35μm in a and 20μm in b