Visualisation of fluid flow by injecting polystyrene beads into the cerebral ventricles of anaesthetised albino X. laevis larvae at stage 47-49. Serial multi-coloured dots represent the trajectories of each bead from 0.7 to 5.3 seconds. The brightness of the video frames are inverted, and the trajectories of the beads were visualised by red - > orange - > yellow - > green - > blue - > purple, in turn, using a combination of Image-J software and its plug-in "Color Footprint Rainbow". (a) The beads diffused into the third cerebral ventricle mainly along the left wall of the ventricle just after the injection. (b, c) The beads moved with left-right asymmetrical circulation in the third ventricle (b) and exited through the cerebral aqueduct along the wall of the third ventricle (c). In many individuals, a left-right asymmetry in bead movements in the third ventricle was observed (see Table 1 and Table 2). (d) Within the lateral ventricles, the beads move along the distal walls toward the medial walls creating a semi-circular movement. (e-h) In the cerebral aqueduct, the beads moved rostrally in the dorsal region [(e) and (g) magnified view of (e)] and caudally in the ventral region [(f) and (h) magnified view of (f)]. (i, j) In the fourth ventricle [(i) dorsal side; (j) ventral side], beads tended to concentrate toward the centre and move to the anterior in the dorsal region, whereas beads tended to flow toward the sides and move to the posterior in the ventral region. cp: choroid plexus; lv: lateral ventricle; ca: cerebral aqueduct (aqueduct of Sylvius). All panels are dorsal views (see Additional file 1: movie 1, Additional file 2: movie 2, Additional file 4: movie 4, Additional file 5: movie 5, Additional file 6: movie 6, Additional file 7: movie 7, Additional file 8: movie 8, and Additional file 9: movie 9). Duration of recording; (a) 5.3 sec; (b) 1.0 sec; (c) 0.9 sec; (d) 1.2 sec; (e) 0.9 sec; (f) 0.7 sec; (i) 1.5 sec; (j) 2.6 sec. Scale bars, 0.1 mm.