The objective of the proposed research is a more complete ultrastructural understanding of the uveal and inner scleral components of the eye, with particular reference to the development of those features which serve the containment of intraocular fluid (IOF) separating it from the general connective tissue compartment of the body and acting as a resistance to IOF pressure. Developmental acquisition of occluding ("tight") junctions among mesenchymally-derived epithelioid uveal cells and/or establishment of special impermeable or high resistance connective tissue matrices are mechanisms by which IOF containment may be served, but neither have heretofore been sought out with modern fine structural techniques. The eyes of hamster embryos and fetuses as well as eyes of developing chicks and amphibians will be studied using scanning, high resolution transmission and freeze-fracture electron microscopy. Patterns of uveal mesenchymal cell behavior during formative stages of the choroid and sclera, and the possible emergence therein of intercellular junctions and/or unique extracellular matrix arrangements will be principal targets of the investigation. In the light of recent fine structural and physiological understanding of various intercellular junctions, this study has fundamental significance for any ocular disease in which the balance of IOF pressure or content is involved.