The ultrastructure of the pecten oculi in the chick

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Abstract
The ultrastructure of the pleats of the pecten oculi was studied in the newly-hatched and adult chick. The blood vessels display several, rather unusual features, such as peri-endothelial cells and numerous microvilli which project into the lumen. Based on the arrangement of the basement membrane, the lack of fenestrations, and the incomplete pericapillary investment, the capillaries belong to the type A-1-[alpha]. In distinction to the findings of other workers, the endothelial lining consisted of cells displaying evident cell membranes and numerous terminal bars. The basement membranes are thickened extensively by additional ground substance material containing reticular microfibrils. Great variation exists in the arrangement of pigment cells. Intercellular spaces, into which numerous pigment cell processes may project, may be present in some areas whereas they are absent in others. Some evidence exists that the covering membrane of the pecten may be continuous with the internal limiting membrane of the retina. The role and the origin of the peripectinate cells, however, remain obscure. It is important to stress the great variation in cellular arrangement and structure encountered as the result of variations in the techniques employed. Consequently the results of experimental investigations need to be interpreted with considerable caution.