What is a hollow sphere of cells during embryonic development called?

During embryonic development, the term for a hollow sphere of cells is referred to as a blastula. This structure forms after several rounds of cell division following fertilization and is an important stage in the development of multicellular organisms.

The blastula consists of an outer layer of cells, known as the blastoderm, surrounding an inner fluid-filled cavity called the blastocoel. This stage is crucial as it precedes gastrulation, where cell layers will rearrange to form the different tissues and organs of the organism.

Understanding the blastula's role helps clarify its significance in embryonic development, distinguishing it from other stages and structures like the zygote, amniotic sac, and ovum, which serve different functions in reproduction and fetal development.