Abstract
The organon vasculosum laminae terminalis has been studied by many investigators in various animals. Recently Weindl et al. ('67)1) studied electron microscopically the organ of the rabbit, particularly the vascular system of the organ. Although there are many investigations on the organ, its function remains obscure. Therefore, in the present study the author attempted to investigate this organ electron microscopically with special reference to the ependymal cells. The ependymal cells, unlike the ordinary ones, have neither cilia nor microvilli. Instead, two kinds of ependymal protrusions can be found, which is confirmed by making their three-dimensional reconstruct ions out of their serial electron micrographs. The first type is not a microvillus, but a fin like thin fold of the apical cytoplasm akin to the marginal fold of Fawcett ('63, '65, '66)2-4). This type of protrusion has not been reported previously in the ependymal cells. The second type is a protrusion of the kind that is irregular in shape and size, and in most cases, it shows "coated" and uncoated invaginations or vesicles. Moreover, in the apical cytoplasm are observed a large number of smooth-surfaced vesicles and some multivesicular bodies and also dense bodies. All these structures are considered to be closely related to absorption.
