Abstract
An unique tubular configuration of the endoplasmic reticulum was discovered electronmicroscopically in a canine thyroid carcinoma. The striking round tubules are aligned parallel to one another and have a regular diameter of about 45 nm. Mostly a number of 3–7 tubules are present in one cisterna of the endoplasmic reticulum, forming a bundle with rather straight course. Longitudinally, a length of up to 5 μm can be traced in thin sections. Continuity of the tubular membranes with those of the endoplasmic reticulum is well established, whereas free endings obviously do not exist. Most of the tubules reveal an internal structure consisting of 1–7 longitudinally oriented filaments. It is suggested that the tubules represent a partial modification of the endoplasmic reticulum. Their relation to well known special arrays of the endoplasmic reticulum is discussed.
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