430 legs and the antennae (Fig. 2a). Interestingly, the expression in the thoracic limb buds extends from there into the lateral tissue of the thoracic segments posterior to the limb buds, and thus is not restricted to the limb buds (Fig. 2a, arrows). A weaker expression is detected in the maxillary and labial segment, where distinct buds are not yet developed. A separate expression domain is present in the anterior head in the region where the labrum will develop. As the germband grows, a punctate expression in the ventral nervous system appears and the expression in the thorax Dev Genes Evol (2009) 219:427–435 becomes restricted to the leg limb buds (Fig. 2b). During later germband elongation stages, the punctate expression pattern in the ventral nervous system becomes stronger and some cells in the brain also express Sp8/9 (Fig. 2c). These brain cells are located at the rim of the head lobes in the area where the optic centers develop and also nearer to the ventral midline in the protocerebrum (Fig. 2c). All limb buds, including the emerging buds of the labrum, the mandibles, and the maxillae, now express Sp8/9. In fully elongated embryos, the expression pattern persists, but the Fig. 2 Expression of Sp8/9 in Oncopeltus embryos. a Early germband elongation stage. Arrows point to expression extending from the thoracic limb buds into the lateral tissue of the thoracic segments posterior to the limb buds. b Mid-elongation germband stage. c Embryo approaching the final stages of germband elongation. d Fully elongated germband stage. e Retracted germband stage. f Magnification of a leg at the retracted germband stage show- ing the expression rings of Sp8/ 9 abutting the presumptive joint constrictions (arrowheads). All embryos are oriented with the anterior end to the left. Abbreviations: lr labrum, an antenna, md mandible, mx maxilla, lb labium, t1 prothoracic leg, t2 mesothoracic leg, t3 metathoracic leg