part of part of occurrent stage 9 motile blastula stage MotB The embryo is composed of 400-500 cells and is no longer surrounded by a fertilization envelope. Most cells have completed at least one additional mitotic division after the early blastula stage and the cell divisions are now less synchronous than at earlier stages. The embryo remains spherical in shape and one cell layer thick. It does not display any morphological indications of the embryonic axes or of the vegetal plate. The cells have started to flatten on their inner (basal) surface, further contributing to the enlargement of the blastocoel, which has expanded since the early blastula stage. ecao_developmental_stage