Stage 23 (1 day 17 hrs)
12 somite stage (Formation of tubular heart)
Drown by T. Iwamatsu
(Abbr. bc: body cavity, bi: blood island, ea: otic (ear) vesicle, fb: forebrain, h: heart rudiment, l: lens, mb: midbrain, no: notochord, od: oil droplet, sm: somite)
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 neuro- coele 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.