Visualisation of bead movements injected into the fourth ventricle within the fourth ventricle in stage 39 (a-c) and stage 42 (d-f) anaesthetised non-feeding embryos. Anterior is to the top. (a) Bright-field image of a stage 39 embryo (dorsal view). Orange box indicates the area of recording in (b). (b) Trajectories of the beads (diameter = 5.8 μm) within the fourth ventricle are shown in a separate embryo (dorsal view). The trajectories show the existence of some flow, but a discrete pattern was not apparent. (c) Magnified view of (b). Note the non-directional bead movements. (d) Bright field image of a stage 42 embryo (dorsal view). (e) Trajectories of the beads (diameter = 5.8 μm) within the fourth ventricle in the same embryo (dorsal view). Note that a radial CSF flow, from the centre of the ventricle toward the wall, is generated at stage 42. (f) Magnified view of (e). See Additional file 10: movie 10. Duration of recording; (b) 2.7 sec; (e) 0.9 sec. Scale bars, 0.5 mm (a, d) and 0.1 mm (b, e).