Fig. 8. A 200-μm thick section of the anterior uvea of a monkey eye, reacted for the demonstration of intravenously injected horseradish peroxidase (HRP). The ciliary body stroma is filled with black, HRP reaction product that has leaked from its fenestrated vessels. The ciliary muscle shows relatively little staining resulting from the nonfenestrated vessels that serve it. The dark coloration of the iris is not HRP but the normal dark pigmentation imparted by the pigmented epithelial layers on its posterior surface.