immediately_preceded_by developmental stage Medaka stage 18 Medaka stage 19 2 somite stage OlatDv:0000220 Zoological Science 11: 825-839 (1994) - 1 day 3 hrs 30 min Stage 19 (1 day 3 hrs 30 min) 2 somite stage: A groove appears in the dorsum of each optic lobe. At the end of this stage (3 somites), two slight knobs are recognized behind the optic vesicles. The blastopore is completely closed. The expansion of the enveloping layer is accomplished without an accompanying increase in the number of constituent cells [18]. - 1 day 3 hrs 30 min medaka_ontology