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1. 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
   - blastosphere

Derived forms: blastulae, blastulas

See also: blastular

Type of: conceptus, embryo, fertilised egg [Brit], fertilized egg

Encyclopedia: Blastula