immediately_preceded_by developmental stage Medaka stage 22 Medaka stage 23 12 somite stage Formation of tubular heart OlatDv:0000260 Zoological Science 11: 825-839 (1994) - 1 day 17 hrs Stage 23 (1 day 17 hrs) 12 somite stage (Formation of tubular heart): The anterior portion of the straight-tubed heart reaches beneath the posterior end of the eye vesicle. A pair of semi-circular Cuvierian ducts (blood vessels) and the vitello-caudal vein begin to form on the yolk sphere. Kupffer's vesicles shrink. The neurocoele is formed in the fore-, mid- and hind-brains. The spherical optic lenses are completed. A blood island becomes pronounced in the ventral region between the 6th and 11th somites. The anterior (the 3rd - 5th) somites assume a slightly dog-legged shape. The oil droplets have coalesced into a single large drop. - 1 day 17 hrs medaka_ontology