Postembryonic development of the optic lobes of Phormia regina meigen (diptera: Calliphoridae)

Abstract

The postembryonic development of the optic lobes of Phormia regina Meigen was studied using reduced silver nerve stains. The ganglion cells of the optic cortices are formed from 2 neuroblast aggregates located within the optic lobes, the inner and outer optic anlagen. The lamina and medulla are formed by the outer optic anlage; and the lobula and lobula plate by the inner optic anlage. One isolated neuroblast was observed to participate in the development of the lobula. The neuropiles and cortices of the lamina, medulla and lobula plate are formed with discrete spatial and temporal orientations, resulting from the distal displacement of ganglion cells from their site of proliferation. In regard to the lamina, medulla and lobula plate, ganglion cells and neuropile located distal to the site of ganglion cell production are older and more differentiated than those located more proximally. The displacement of ganglion cells also results in specific directions of formation for the lamina, medulla and lobula plate and the formation of the first optic chiasma. The lamina forms in a posterior-to-anterior direction; the medulla and lobula plate in a medial-to-lateral direction. The first optic chiasma forms because the lamina and medulla form in opposite directions and the fibers extending between them cross-over one another and form a chiasma.