1. Blastosphere: 1 n 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 Synonyms: blastula Types: blastocyst , blastodermic vessicle the blastula of a placental

2. Blastocyst - the blastula of a placental mammal in which some differentiation of cells has occurred blastodermic vessicle 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

3. Blastosphere definition: 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 synonyms: conceptus, blastodermic vessicle, cleavage cavity, trophoblast, embryo, blastocoel, blastula, blastocoele, blastocele