develops from external sensory organ precursor cell external sensory organ precursor cell IIb external sensory organ precursor cell IIIb pIIIb fly_anatomy.ontology The reference paper (Gho et al., 1999) provides evidence for the existence of this intermediate stage between pIIb and the birth of the eo neuron in the wing mechanoreceptor development. There may be some question as to whether this can be generalized to all external sensory organs, but in the absence of evidence that the development of these organs is distinct I have applied this stage to all external sensory organ development. ds060308. FBbt:00006022 Precursor cell daughter of an external sensory organ precursor cell IIb. In the development of antennal olfactory sensilla, there are two classes, pNa and pNb, which each divide asymmetrically to produce up to four types of sensory neuron per sensillum (Endo et al., 2012; Chai et al., 2019). In the microchaete lineage, there is one of these cells (the other daughter of pIIb is a glial cell), which divides to produce one neuron and one apical sheath cell (Gho et al., 1999).