Intracisternal tubules and intramitochondrial filaments in cells of a snail, Limnaea.

Epithelial and peritubular cells associated with the reproductive tract of the snail, Limnaea stagnalis, contain an extensive system of endoplasmic reticulum that is often dilated with many closely packed intracisternal tubules. The intracisternal tubules are approximately 24-28 nm in diameter and they are often hexagonally packed. They have a two-layered wall, possess fine interconnections, and extend linearly for considerable distances, but angular bends in the tubules also occur. Mitochondria in the peritubular cells contain solid, filamentous structures 9-12 nm in diameter and triangular-shaped structures when sectioned in the mitochondrial matrix.