Fig. 2. Schematic diagram showing secondary fiber development or lens growth at selected stages. Lens epithelial cells in the peripheral GZ undergo mitosis and some daughter cells are selected to terminally differentiate into secondary fibers. As these cells migrate posteriorly, their shape changes from low cuboidal to high columnar and finally to elongate, crescent fiber. However, it is most important to note that the in addition to a crescent curvature, the ends of most secondary fibers have additional curvature in opposite directions away from the polar axis but within growth shells.