Summary
The fine structure of blood capillaries and their surroundings in the hemispheres of the hagfish, Myxine glutinosa, is described. As in other species, one or more endothelial cells delinate the lumen. Where such cells meet, they show complicated interdigitations. At some places tight junctions (“zonulae occludentes”) are found.
The cytoplasm pressents at places many glycogen particles, ergastoplasmic membranes and free ribosomes in addition to the usual organelles. In addition, the luminal surface gives origin to deep invaginations from which channels penetrate into the cytoplasm. Numerous, presumably pinocytotic vesicles ranging from 450–1000 Å in diameter are present in the endothelial cell cytoplasm. A special type of cytoplasmic tubules is also present. The basement membrane is very thick, and measures 1000 Å at the narrowest place.
Only one type of glial cell is present. This cell has certain characteristics in common with astrocytes of mammals but is for certain reasons considered to be a primitive glial cell. All capillaries have a complete lining of glial elements. The glial processes in contact with the vessels vary in shape and size. Glia cell bodies also participate. Closed contacts are present between the glial cells, but also desmosomal attachments are observed.
The finding that capillaries in the hemispheres of Myxine are entirely surrounded by processes or bodies of glial cells shows that even at the most primitive vertebrate level glial cells are essential for the transport of material from the blood into the nervous tissue.
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Addendum. After the paper was submitted for publication, Dewey and Barr have considered the possible role of the „zonulae occludentes“ in electronic coupling between cells [J. Cell Biol. 23, 553–585 (1964)]. The reader is referred to this paper.
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Mugnaini, E., Walberg, F. The fine structure of the capillaries and their surroundings in the cerebral hemispheres of Myxine glutinosa (L.). Zeitschrift für Zellforschung 66, 333–351 (1965). https://doi.org/10.1007/BF00334716
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DOI: https://doi.org/10.1007/BF00334716