A. Introduction B. Materials and Methods C. General Topography D. The Normal Structure 1. Nonpigmented epithelium a. Internal limiting membrane b. Cell membrane and β-cytomembranes c. α-Cytomembranes d. Golgi apparatus e. Mitochondria f. Nucleus g. Granules h. Ground substance 2. Pigment epithelium a. Cell membrane and β-cytomembranes b. α-Cytomembranes c. Golgi apparatus d. Mitochondria e. Nucleus f. Granules g. Ground substance h. External limiting membrane E. Alterations in Structure and Function 1. Appearance of epithelium in young rabbits 2. Apperance of epithelium after treatment with acetazolamide F. Comment G. Conclusion H. Summary A. Introduction Since the publication of the analysis of the ultrastructure of normal and acetazolamide (Diamox)-treated nonpigmented ciliary epithelium in the rabbit eye (Holmberg, 1957), the investigation has been extended to include the pigment epithelium in adult rabbit and both epithelial layers in monkey, human, and young rabbit eyes. The ultrastructure of the ciliary body capillaries and of