Cobalt filling of sensory projections from internal and external mouthparts in Drosophila.

Phase-contrast microscopy of 2.5 micron plastic sections reveals five different kinds of sense organs on the internal mouthparts of Drosophila melanogaster: a ventral group of sensilla on the epipharynx, three kinds of sense organs in the middle part of the sucking apparatus (the cibarium), one of them being described here for the first time, and an additional type of sensillum in the dorsal pharynx (Fig. 1). Three of these internal sense organs resembling each other structurally form similar projection patterns in the tritocerebrum, whereas external taste receptors on the labial palps show a different pattern in the suboesophageal ganglion (Fig. 12). The central projections of these internal and external sensilla were traced by applying an ethanolic solution of cobalt on the intact cuticle.