Fig. 8. When the embryo has reached approximately 25 mm in length, the lens epithelium undergoes extensive proliferative activity. The newly formed cells begin to internalize at the equator and elongate into secondary fibers. Fibrogenesis is marked by the reorientation of the cells in the anteroposterior direction. The basal portions of the cells elongate posteriorly, while the apices of the cells proceed anteriorly. Continued deposition of new cells at the equator causes previously deposited cells to be buried in the lens substance. A continual accretion of these cells at the equator is the basis of the continued growth of the lens throughout life.