Fig. 1.

Glycol methacrylate sections from a 6-WG embryonic human eye. A: At low magnification (A), the lens (L), retina (R), optic nerve (ON), and choroid (C) are apparent. Vitreous (V) fills the chamber between lens and retina. B: Magnification of the boxed area in A, where the relationship between retina, the monolayer of retinal pigment epithelial (RPE) cells, and choroid can be seen. Arrows point to the forming choriocapillaris. The separation between retina and RPE is artifactual. A,B: Hematoxylin and eosin. Serial, Wright’s Giemsa-stained, sections of retinal pigment epithelial cells (RPE) (top in all) and developing choriocapillaris (below RPE) are shown in C–K. C: A single cell with moderately acidophilic (pink) cytoplasm is present just posterior to the pigmented RPE cells (top). D,E: Nucleated cells aggregate in this area that have intensely acidophilic cytoplasm, which is a characteristic of embryonic hemoglobin staining in erythroblasts. F–H: Mesenchymal-like cells with spindle-shaped nuclei become part of the aggregate or island of cells and in some areas appear to surround the erythroblasts while in other areas the erythroblasts form the outside of the aggregate (F). I–K: The island divides into several clusters of cells and individual erythroblasts as well. L,M: At higher magnification, the lumen-like nature of the center of the aggregate becomes more apparent and the presence of several types of cells in the center of the island is more obvious.