developmental stage Medaka stage 2b OlatDv:0000050 Zoological Science 11: 825-839 (1994) - 60 min Stage 2b (60 min) Blastodisc stage b: The male and the female pronuclei migrate toward and associate with each other at the center of the thick cytoplasmic disc at the animal pole. Chromosomes then appear and divide into two groups at the poles of the spindle marking the end of this stage. The layer of cortical cytoplasm covering the yolk sphere is very thin except where it forms the cap-shaped blastodisc. By the end of this stage, most of the oil droplets from the animal hemisphere have already migrated to the vegetal hemisphere. Two dimple-like pits on the blastodisc serve as markers to locate the future blastomeres. - 60 min blastodisc stage b medaka_ontology