part of develops into developing embryonic structure primordium mushroom body primordium Embryonic structure from which the mushroom body is derived. The development of the mushroom body proceeds as follows: axonogenesis of embryonic Kenyon cells starts late in embryonic stage 14. The axons from these cells extend towards the lateral protocerebral tract (LTP). During stage 16, a second set of Kenyon cell fibers form a second tract, closely apposed to the first. By late stage 16, both tracts extend anteriorly beyond the LTP to form the distal part of the peduncle. These tracts make a sharp medial turn close to the boundary with the deutocerebrum to form the medial lobe. By late stage 17 the vertical lobe has emerged as a collateral outgrowth from the point where these tracts bend. Finally, the calyx forms near to the end of embryogenesis. embryonic central brain mushroom body FBbt:00005666 FBbt:00005508 VFB:FBbt_00005508 fly_anatomy.ontology central brain primordium embryonic central brain mushroom body anterior ectoderm derivative