develops from develops into prothoracic gland prothoracic gland primordium FBbt:00005497 fly_anatomy.ontology The primordium that will form the embryonic/larval prothoracic gland, a substructure of the embryonic/larval ring gland. It originates in the dorsal ectoderm of T1, from which it segregates during stage 15 to form bilateral clusters near the heart precursors. In late embryogenesis, it partially fuses with the corpus allatum. dorsal sensory complex primordium dorsal ectoderm derivative ring gland primordium