substage of immediately preceded by developmental stage oogenesis stage S12C oogenesis stage S13 oogenesis stage S13A FlyBase_development_CV Temporal ordering number - 10210. 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. FBdv:00005279 Oogenesis stage during which 12-15 nurse cell nuclei remain at the anterior of the oocyte. At this stage, the oocyte nucleus has reached its maximum volume and its chromosomes are compressed into a 5-7 micrometer karyosome.