blastocoele /blas″təsēl′/ [Gk, blastos, germ, koilos, hollow] , the fluid-filled cavity of the blastocyst in mammals and the blastula or discoblastula of lower animals. The cavity increases the surface area of the developing embryo to allow better absorption of nutrients and oxygen. Also called cleavage cavity, segmentation cavity, subgerminal cavity. Also spelled blastocoel, blastocele.