Fig. 1. (A-C) SEM images of the external chemosensory organs of the larval head. (A) Frontal overview; (B) enlarged view of the ventral organ (VO) and (C) dorsal (DO) and terminal (TO) organs. VO and TO probably have gustatory functions, whereas the DO serves both gustatory and olfactory functions. MH, mouth hook. The arrow in C points to one of the pores of the dome (DM). Scale bars, 20 µm. (D) Expression of the lacZ reporter in the Gal4 driver line MJ94, showing the position of the larval eye - the Bolwig's organ (BO) - in front of the cephalopharyngeal skeleton (dark brown). Further reporter expression also visualizes the positions of DO, TO and the dorsal, ventral and posterior pharyngeal gustatory sensilla (DPS, VPS, PPS). Scale bar, 100 µm. (E) Wiring diagram showing the central projections of the head sensory organs to the optic lobe (OL) tritocerebrum (TR), suboesophageal ganglion (SOG) and antennal lobe (AL) (modified from Python and Stocker, 2002a). AN, BN, LN, MN and LBN: antennal, Bolwig, labral, maxillary and labial nerves, respectively. LI, PN, local interneurons of the AL, projection neurons; LPR, lateral protocerebrum; MB, mushroom bodies; PH, pharynx.