Timelapse of dorsal side during gastrulation shows migration of hypoblast and underlying yolk syncytial layer (YSL) nuclei (larger bright spots). The prechordal plate can be seen as a more clumped mass of cells as it moves toward the animal pole. Alexa-Histone injected into YSL, free Alexa permeates to label deep cells in blastoderm. Sphere is approximately 700 microns in diameter. Video made available through Mark Cooper and Zebrafish The Living Laboratory.