part of develops into developing embryonic structure late extended germ band embryo fat body primordium gonadal sheath proper primordium primordium fat body/gonad primordium Primordium which develops into the fat body and gonadal sheath. The cells that comprise it are specified from stage 10 (Jemc, 2010), though the first morphological sign of its development comes during stage 11, when the outer of the two layers of the trunk mesoderm thickens medially to become 2-3 cells thick. Segmentally arranged groups of cells split off from inner most layer of this thickening, becoming sandwiched between the somatic muscle primordium and the circular visceral muscle primordium. By stage 13, these segmental clusters have fused into continuous columns on either side of the embryo. These bands split into dorsal and ventral subdivisions. A sub-population of cells in the dorsal subdivision in parasegments 10-12 split off to form the gonadal sheath primordium during stage 14-15. The other cells then form the fat body primordium proper. bipotential lateral mesoderm FaB/GP2 fly_anatomy.ontology FBbt:00005520 P2 FaB/GP gonadal mesoderm somatic trunk mesoderm derivative