The view is from the animal pole. The focal plane is deep within the blastoderm. The focal plane changes as the embryo rolls during the sequence.
Deep cells undergo radial intercalation to form a coherent sheet known as the hypoblast.
The dark centers which come into view are nuclei located within the yolk syncytial layer. The embryo rolls once again. The sequence ends with a cross-sectional view of the enveloping layer ensheathing the embryo. The head anlage lies between the enveloping layer epithelium and the brightly labelled yolk cell.