Left panel, schematic illustrating the anatomy at the 2 bony ray stage (endothelium, cyan; osteoblasts, yellow). Middle panel, still image of the developing endothelial spout/plexus labeled by Tg(fli1a:EGFP) at the 2 bony ray stage. Right panel, DIC video of blood flow in the developing endothelial spout/plexus. White arrow points to the position of blood cells travelling ventrally through the HD into the developing plexus. Time is displayed as MM:SS. Scale bar, 50 μm.