part of develops from develops into embryonic/larval gonadal sheath muscle cell developing embryonic structure dorsal closure embryo gonadal sheath proper primordium gonadal sheath specific anlage The primordium of the gonadal sheath. This arises from clusters of cells in parasegments 10, 11 and 12 of the dorsal branch of the fat body/gonad primordium which split off during stage 14 and then cluster around the germ cells. gonadal mesoderm fly_anatomy.ontology somatic gonadal precursor FBbt:00005473 SGP primordium fat body/gonad primordium somatic trunk mesoderm derivative visceral trunk mesoderm derivative