Ciliates such as Paramecium have specialized sites for endocytosis and exocytosis. Most of their surface is not available for internalization of membrane because of the underlying alveolar sac system. However to the right of each basal body or pair of basal bodies is an indentation of the plasma membrane called the parasomal sac. This penetrates through the septum and ends as a coated pit. This micrograph also illustrates the normal view of mitochondria in P. caudatum which are filled with tubular cristae. In cacodylate-buffered fixations the cytosol contains abundant electron-opaque glycogen storage granules which seem to be removed during collidine-buffered fixations. TEM taken on 5/28/69 by R. Allen with Philips 300 operating at 60kV. Neg. 14,800X.