noun.
An early embryonic form produced by cleavage of a fertilized ovum and consisting of a spherical layer of cells surrounding a fluid-filled cavity.
The Century Dictionary and Cyclopedia
noun.
In embryology: An embryo of one of the Metazoa, in the stage in which it consists of a sac formed of a single layer of cells.
noun.
In Haeckel′ s vocabulary of embryology, same as blastosphere, .
the GNU version of the Collaborative International Dictionary of English
noun.
That stage in the development of the ovum in which the outer cells of the morula become more defined and form the blastoderm.
noun.
An early form in the development of an embryo, consisting of a sphericallayer of cells filled with fluid; a blastosphere.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
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
Word Usage
"It’s not a solid ball but a hollow one, and it is called the blastula."