ANALYSIS OF NEURAL ELEMENTS IN HEAD-MUTANT DROSOPHILA EMBRYOS SUGGESTS SEGMENTAL ORIGIN OF THE OPTIC LOBES

We describe the development of 20 sensory organs in the embryonic Dros ophila head, which give rise to 7 sensory nerves of the peripheral ner vous system (PNS), and 4 ganglia of the stomatogastric nervous system (SNS). Using these neural elements and the optic lobes as well as expr ession domains of the segment polarity gene engrailed in the wild-type head of Drosophila embryos as markers we examined the phenotype of di fferent mutants which lack various and distinct portions of the embryo nic head. In the mutants, distinct neural elements and engrailed expre ssion domains, serving as segmental markers, are deleted. These mutant s also affect the optic lobes to various degrees. Our results suggest that the optic lobes are of segmental origin and that they derive from the ocular segment anteriorly adjacent to the antennal segment of the developing head.