Scanning electron microscopy of the developing chick anterior corneal epithelium.

The anterior corneal epithelium of the developing chick was observed with the scanning electron microscope at various stages of development. In the earlier stages, up to about 15 days of incubation, the cells are characterized by regular polygonal outlines and a proliferation of microvilli on the surface. The microvilli then begin to coalesce and flatten so that the surface is rather smooth by about 19 days of incubation. Just prior to hatching, however, the cells begin to round up and once again become covered by microvilli. The cells then lift off the surface and expose the underlying cells. After hatching, the surface cells lose the synchrony of development that characterized the embryo and are found in various stages of senescence. The cells eventually lose their regular polygonal outlines and the corneal surface takes on a patchwork appearance.