EMBRYONIC-DEVELOPMENT OF THE CORNEA IN THE EYE OF THE CLEARNOSE SKATE, RAJA-EGLANTERIA .1. STROMAL DEVELOPMENT IN THE ABSENCE OF AN ENDOTHELIUM

Embryos of the clearnose skate, Raja eglanteria, develop in sea water at 20-22 degrees C, hatching after 82 +/- 4 days (Luer and Gilbert, En viron.. Biol. Fishes, 13:161-171, 1985). Eyes develop as steadily enla rging spheres whose corneas have the same radius of curvature as the s clera. The cornea begins development as a 2-cell thick epithelium bene ath which by Day 12 there is only a basal lamina and a wispy matrix se parating it from the underlying lens. This matrix, modified by Day 16, is displaced on Day 22 by a few orthogonal plies of fibrillar primary stroma. Ply number increases to at least 13 by Day 30, reaching the f inal number of 20 +/- 2 by Day 42. Stromal fibroblasts (keratocytes) a ppear at the corneal periphery by Day 22, and in increased numbers by Day 30, a time at which no keratocytes are seen in the central stroma. However, by Day 40, many fibroblasts are present at the corneal perip hery, invading the primary stroma between plies, occasionally reaching even the central cornea. By Day 53, keratocytes are present between a ll plies, from corneal periphery to center. Thickness of each ply in t his secondary stroma increases, but the number of plies remains the sa me as in the primary stroma. Bowman's layer, non-invaded matrix beneat h the epithelial basal lamina, is not evident until Day 53. Sutural fi bers, first seen on Day 22, originate in the corneal epithelial basal lamina, traversing perpendicularly the plies of the primary stroma. Su tural fibers persist throughout development of the secondary stroma an d into adulthood. In contrast to chicks, skate corneas remain transpar ent throughout development, and never form an endothelium. (C) 1994 Wi ley-Liss, Inc.