gastric caecum primordium fly_anatomy.ontology embryonic gastric caecum FBbt:00005629 Primordium of the gastric caecum of the larva. There are four of these per midgut. They first become apparent as evaginations at the anterior end of the fused midgut primordium during stage 16. FBbt:00017027 FBbt:00005629 embryonic structure