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.
This embryo, resembling a hollow rubber ball filled with fluid, is called a blastosphere.
2
The earliest one-celled protozoa were probably succeeded by many- celled animals of the type of the blastosphere, and these by gastrula-like organisms.
