Here you can see the lens development process at work in a cross section of tissue from an adult mouse. In mice, as in humans, a single layer of rod-like epithelial cells (far left, blue/green) gives rise to specialized lens cells (middle, blue/green) throughout life. The new cells resemble their progenitor cells, with the nuclei (blue) and cytoskeletal protein actin (green). But soon these cells will produce large amounts of water-soluble proteins, called crystalline, to improve their transparency, while gradually breaking down their nuclei to eliminate light-scattering mass. What remains are fully differentiated, enucleated, non-replicating lens fibrous cells (right, green), which refract light onto the retina at the back of the eye.