A cytoplasmic structure exhibiting a peculiar configuration of agranular reticulum has been found in the rat pinealocyte, and has been designated a canaliculate lamellar body. It consists of a number of fenestrated, flat cisternae which are closely spaced. They bear some distant resemblance to the annulate lamellae previously reported in a variety of cell types. Profiles of stacks of lamellae in a plane of section always display two distinct aspects, the surface and the cross-sectional views of flat cisternae. A surface view shows the hexagonal arrangement of pores or fenestrations. The pores in successive lamellae are aligned precisely, one behind the other, so that clear, cylindrical channels are seen running perpendicular to the lamellae as indicated by transverse sections of the lamellar stacks. Large canaliculate lamellar bodies are composed of many extended series of lamellar stacks which pursue a tortuous course and cross one another. Occasionally the canaliculate lamellar body is located deep in a nuclear invagination, which reminds one of the so-called nuclear pellets (Kernkugeln) reported by light microscopy. The functional significance of the body is unknown.
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