They remain in ProPhase one of meiosis until puberty is reached. And when that female individual reaches puberty, she begins the process known as the menstrual cycle. And what the menstrual cycle describes is it describes the process by which the primary ocy eventually develops into that X cell, that single ovum that can be fertilized by the sperm cell to produce the zygote. So when the female reaches puberty, a cycle begins known as the menstrual cycle, in which one primary oocyte will eventually undergo meiosis one to produce a secondary oocide which will remain frozen in metaphase II of meiosis until the process of fertilization. And during fertilization, meiosis II will be completed and aromature ovum, the excel, will be formed. So to see exactly what we mean by that, let's take a look at the following diagram.