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|Noun||1.||blastosphere - early stage of an embryo produced by cleavage of an ovum; a liquid-filled sphere whose wall is composed of a single layer of cells; during this stage (about eight days after fertilization) implantation in the wall of the uterus occurs|
conceptus, fertilized egg, embryo - an animal organism in the early stages of growth and differentiation that in higher forms merge into fetal stages but in lower forms terminate in commencement of larval life
blastocele, blastocoel, blastocoele, cleavage cavity, segmentation cavity - the fluid-filled cavity inside a blastula
blastocyst, blastodermic vessicle - the blastula of a placental mammal in which some differentiation of cells has occurred
trophoblast - the membrane that forms the wall of the blastocyst in early development; aids implantation in the uterine wall; "after implantation of the blastocyst in the uterine wall the trophoblast divides into two layers, the chorion and the placenta"