The pineal gland of the hamster has been examined with the electron microscope. The gland is composed of two types of parenchymal cells, a “light” and a “dark” cell. Blood vessels are infrequently encountered and display little perivascular space. Axons, nerve endings, pineal cell processes, and occasional glial processes ramify within the parenchyma of the gland. The parenchymal cells display abundant mitochondria, many with a tubular internum. Smooth and rough surfaced endoplasmic reticulum, a Golgi apparatus and lipid droplets are regular features of both cell types. Vesicles of varying size and containing electron dense centers are present in the cell body. Parenchymal cells branch extensively and are characterized by the presence of microtubules in addition to the usual organelles encountered in the cell body. Pineal cell process terminations regularly show accumulations of vesicles with electron dense granulations.
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