- blastula, blastodermic vesicle - 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
--1 is a kind of embryo, conceptus, fertilized egg
--1 has parts:
--1 has particulars: blastosphere, blastocystblastocoel, blastocoele, blastocele, segmentation cavity, cleavage cavity