Blastulas

A blastula is a stage in early embryonic development. It is a hollow sphere of cells formed after fertilization and prior to gastrulation. The blastula is a crucial stage in development, as the cells go on to differentiate, eventually forming the body structures and organs of the organism. In humans, the blastula stage can be seen four or five days after fertilization. This stage is also significant for the study of stem cells, as the cells in the blastula are undifferentiated and can be used for medical treatments such as those for degenerative diseases.