A blastocoel(e) or blastocele or cleavage cavity or segmentation cavity is the central region of a blastula (or blastosphere). It is filled with fluid. A blastocoele forms during embryogenesis when a zygote (a fertilized ovum) divides into many cells through mitosis.
The adjectival of "blastocoel(e)" is blastocoelic.
See also: embryo