A prominent feature of one class of astrocytes is the presence of large numbers of 9 to 10 nm cytoplasmic filaments occurring throughout the perikaryon and extending into the cell processes. They are said to be slightly smaller than neurofilaments and instead of being distributed individually, they tend to be aggregated in conspicuous bundles. A large bundle of closely packed filaments coursing along a mitochondrion in a glial cell process is shown in the accompanying micrograph.