A 4D visualization of zebrafish somitogenesis and neural keel formation. The Quicktime movie shows progressively dorsal optical sections in a segmenting embryo. Note the midline alignment of neuroepithelial cells in the presumptive floorplate region. This alignment reflects the location of the neural midline and is the first overt morphological sign of bilateral symmetry in the neural rudiment. Video made available by Mark Cooper through Zebrafish - The Living Laboratory.