part of overlaps develops from larval tracheal system embryonic/larval spiracle fly_anatomy.ontology Spiracle of the embryo or larva. In the latter, there are 10 pairs of spiracles, but only the most posterior is functional at all larval instars. The anterior spiracle becomes functional at the second larval stage. FBbt:00005600 FBbt:00000406 larval spiracle larva spiracle embryonic/larval spiracle primordium