Zebrafish embryo at 80% epiboly. The initial frame shows the junction of the enveloping layer with the yolk cell. The next frame is at a focal plane deeper within the embryo. The blastoderm margin is visible. Dark nuclei within the yolk syncytial layer are also apparent. As the sequence progresses, one sees closure of the blastopore. The ending sequence shows a small opening--the remnant of the yolk syncytial layer--and a constricted germ ring. This video made available by Mark Cooper thru Zebrafish - The Living Laboratory. The videos in this group can also be found in the Developmental Landmarks page of the Fishscope web site.