secondary oocyte, an oocyte in the period between the first and second maturation division. It is derived from a primary oocyte shortly before ovulation by a division that splits off the first polar body. If fertilized, it divides into an ootid and the second polar body. Otherwise, it perishes. In humans, it is a round cell about 0.1 mm in diameter and consists of protoplasm that contains some yolk enclosed by a thin cell wall, the vitelline membrane. It is surrounded by the zona pellucida and corona radiata.
