MAURIZIO DE ANGELIS / SCIENCE PHOTO LIBRARY MAURIZIO DE ANGELIS / SCIENCE PHOTO LIBRARY
Human egg cell. Computer illustration of a human ovum (egg cell), showing the zona pellucida (outer layer). After fertilisation the nuclei of the sperm cell and the ovum fuse to form a zygote. The zygote then undergoes repeated mitosis (cell division). Cell division occurs approximately every twenty hours, to form a cluster of cells known as a morula, which continues to divide to form a blastocyst, and subsequently the embryo.
Model release not required. Property release not required.