When a female is born her ovaries already contain all the eggs (ova) that she will produce in her lifetime. These are initially undeveloped eggs and it is only after the process of puberty that they will become viable. Usually only one egg will complete the maturation process at a time and it is the egg released during the process of ovulation.

Follow the link to view the menstrual cycle animation seen in class:

Menstrual Cycle animation

The following video also comments on the topic:

Menstrual Cycle Data Analysis

The Menstrual Cycle Flash Cards
Menstrual Cycle Flashcards pt 1
Menstrual Cycle Flashcards pt2