Wadeson, P. H., and K. Crawford. 2003. Formation of the blastoderm and yolk syncytial layer in early squid development. 2003. Biol. Bull. 205:179-180.

To view the videos, click the links below.

Movie 1. Early cleavage through blastoderm formation, 4-16.5 hours post-fertilization (hpf), 21°C, observed with a Zeiss Stemi SV 11 stereomicroscope with a 1.6x Planapochromat lens. Images were captured every 5 min. In this video, first cleavage has already begun, and two small polar bodies are visible in the top half of this furrow. Second cleavage occurs perpendicular to the first, and third cleavage is unequal, resulting in the formation of four large blastomeres that mark the future anterior of the developing embryo. The polar bodies reside in or near the anterior midline. Fourth cleavage separates the inner blastomeres from their outer syncytial sister cells. Cleavage is synchronous through 8th cleavage, originating at the apex of the animal pole and radiating out across the embryo. Rapid nuclear movements are also visible during many of these cleavage events. Sixth cleavage continues to separate the inner blastoderm from the syncytial blastoderm and later correlates with the boundary of the cellular blastoderm that forms as cell movements begin.

Movie 2. Blastoderm formation to the onset of epiboly, 26-27.5 hpf, images were collected at 7-min intervals at 21°C. At the start of this sequence, a distinct blastoderm has formed and is surrounded by radiating pairs or clusters of outer blastomeres. As development continues, the blastomeres closest to the blastoderm migrate toward the center, while their outer sister cells simultaneously collapse into the cortex of the yolk cell. At the end of this video, the migrating cells become incorporated into the blastoderm, while their sister cells have become part of the yolk syncytial layer.