A morula is an embryo at an early stage of embryonic development, consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida.
The morula is produced by embryonic cleavage, the rapid division of the zygote. Once the zygote has divided into 8-32 cells, it begins to resemble a mulberry, hence the name morula (Latin, morus: mulberry).
This happens in mammals.
In humans this state is reached about 3 days after fertilization. At this point in time the clump of cells is usuall situated within the fallopian tube.
