part of part of immediately preceded by immediately preceded by occurrent mid-blastula stage stage 10 late blastula stage B4 LB pre-HB prehatched blastula Late-B The embryo is composed of about 600-1000 cells. Most cells have completed at least one additional mitotic division since the mid-blastula stage and developed an apical cilium. The embryo is still spherical in shape and one cell layer thick. It still lacks obvious morphological landmarks of the embryonic axes and of the vegetal plate. Cells have further continued to flatten along the apical-basal axis, accentuating the enlargement of the blastocoel. They are also now joined to one another apically by septate and adherens junctions and laterally by desmosomes. ecao_developmental_stage