substage of immediately preceded by developmental stage oogenesis stage S13 oogenesis stage S13A oogenesis stage S13B FlyBase_development_CV FBdv:00005280 Oogenesis stage during which 9-11 nurse cell nuclei remain at the anterior of the oocyte. During this stage, the nuclear membrane of the oocyte nucleus disappears, indicating the start of meiotic pro-metaphase. Temporal ordering number - 10220. An alternative division of stage 13 into two sub-stages, A and B, has been defined on the basis of chorion development (see FBrf0043885). This ontology uses an alternative subdivision based on nurse cell nucleus number and oocyte meiosis, as the former at least, is easier to score than chorion ultrastructure.