ABSTRACT
Based on the expression pattern of the segment polarity genes engrailed and wingless during the embryonic development of the larval head, we found evidence that the head of Drosophila consists of remnants of seven segments (4 pregnathal and 3 gnathal) all of which contribute cells to neuromeres in the central nervous system. Until completion of germ band retraction, the four pregnathal segment remnants and their corresponding neuromeres become arranged in an S-shape. We discuss published evidence for seven head segments and morphogenetic movements during head formation in various insects (and crustaceans).
In contrast to Wiesmann, Scholl (1969) believes that in Carausius (Phasmida) the second (optic) pair of coelomic cavities in front of the antennal segment derives from the intercalary coelom.
