Fig. 7. A section through the eye of a human embryo at approximately the 18-mm stage. The lumen of the lens vesicle has been completely eliminated by the forward progression of the primary fibers. The anterior ends (the apices of the fibers) adjoin the apices of the epithelial cells. The epithelial cells appear more cuboidal than at previous stages, and the innermost cells of the primary fiber mass are beginning to denucleate. Carnegie embryo 5537. (Courtesy of Victoria Ozanics, Columbia University)