Lens Regeneration in Amphibians
It is an amazing fact that between all vertebrates only certain amphibians have the unique ability to regenerate lens, iris and retina in adult lire. The amphibians also change in their capability to regenerate a lens and in the source of cells from which a new lens is formed. Members of sub-order salamandridae (salamander, Triturus) have the significant ability of growing a new lens from the dorsal iris epithelium (neural ectoderm).
This is a unique instance of metaplasia, as the regenerating iris is derived from neural ectoderm and may be regarded as an extension of the brain whereas the original lens is derived from the epidermal ectoderm. This kind of regeneration has demonstrated that even adult differentiated cells can keep their potential to produce other cell types. In the larvae of the South African frog. Xenopus laevis an invagination of corneal epithelium gives increment to a ball of cells which transforms into the new lens. The procedure of the new lens regeneration in X. laevis more closely duplicates the embryonic process, like both the first lens and the regenerate lens develop from cells of epidermal ectodermal origin, though, even so it is a case of metaplasia, since differentiated cells of corneal epithelium give rise to lens cells that are morphologically and biochemically very different from those of the corneal epithelium. The regenerating capability in this anuran however species disappears at metamorphosis.