|Source: Centro Riproduzione Assistita, Catania, Italy.|
Note:This 12-cell embryo is now at the earliest stage at which the embryo can be called a "morula," which is the scientific word used to describe a ball of cells. This term will continue to apply until a cavity begins to form inside this spherically shaped clump of cells. The age is approximate.
1. zona pellucida
2. perivitelline space
|All ages referenced to fertilization, not last menstrual period.|