part of larval tracheal system developing embryonic structure tracheal precursor cell FBbt:00005041 fly_anatomy.ontology Somatic cell that gives rise to the larval trachea. At embryonic stage 10 the tracheal precursor cells form ectodermal placodes that invaginate to form the tracheal pits by early stage 11. After invagination, the cells in the pit become tracheal cells and begin to form branches, the epidermis fuses, closing the pit and leaving a spiracular branch joining the trachea to the epidermis. somatic precursor cell