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|Noun||1.||fertilized egg - 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|
animal, animate being, beast, creature, fauna, brute - a living organism characterized by voluntary movement
blastosphere, blastula - 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
gastrula - double-walled stage of the embryo resulting from invagination of the blastula; the outer layer of cells is the ectoderm and the inner layer differentiates into the mesoderm and endoderm
morula - a solid mass of blastomeres that forms when the zygote splits; develops into the blastula