Summary
Distal to the flame cells, the protonephridial tubules of fresh-water planarians are circumferentially composed of at least two cells attached by septate junctions; and may be divided, on the basis of morphological criteria, into three longitudinal regions. The cells of nonciliated ductules and ciliated collecting ducts appear to be absorbing material from the lumen; and a distinct proximal-distal polarity is present in each individual cell. At the proximal pole are concentrated micropinocytotic caveolae with amorphous and structural coats on the luminal and cytoplasmic surfaces, respectively. Proceeding distally, a Golgi complex is situated between the micropinocytotic vesicles and large, basophilic, paracrystaline granules. This unusual polarity is interpreted to be important to the resorptive function of the cells.
In four areas of the worm, the branched collecting ducts combine to form single osmoregulatory (O. R.) ducts. The O. R. cells have many mitochondria located in slender processes formed by basal and lateral invaginations and interdigitations. The adjacent plasmalemmas of normally fixed cells are separated by a 180 Å gap; but higher tonicity fixative shrinks the cells, increasing the apparent extracellular space. The O. R. cells differ from analogous cells in higher animals in their function as an osmoregulatory epithelium in the absence of a basement membrane.
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References
Anderson, E.: Oocyte differentiation and vitellogenesis in the roach, Periplaneta americana. J. Cell Biol. 20, 131–155 (1964).
Braun, G., G. Kümmel, and J. A. Mangos: Studies on the ultrastructure and function of a primitive excretory organ, the protonephridium of the rotifer Asplanchna priodonta. Pflügers Arch. Ges. Physiol. 289, 141–154 (1966).
Curran, P. F., and J. R. McIntosh: A model system for biological water transport. Nature (Lond.) 193, 347–348 (1962).
Dresner, I.: Effect of incubation in controlled media on the fine structure of the collecting tubule in the albino rat (Rattus rattus). Anat. Rec. 160, 341 (1968).
Graham, R. C. and M. J. Karnovsky: The early stages of absorption of injected horseradish peroxidase in the proximal tubules of mouse kidney: Ultrastructural cytochemistry by a new technique. J. Histochem. Cytochem. 14, 291–302 (1966).
Hyman, L. H.: The invertebrates, vol. II. New York: McGraw-Hill Bock Co. 1951.
Kaye, G. I., and N. Lane: The epithelial basal complex: a morphophysiological unit in transport and adsorption. J. Cell Biol. 27, 50A (1965).
Martin, A. W.: Comparative physiology (excretion). Ann. Rev. Physiol. 20, 225–242 (1958).
McKanna, J. A.: Fine structure of the protonephridial system in planaria. I. Flame cells. (In press) (1968).
Pedersen, K. J.: Studies on the nature of planarian connective tissue. Z. Zellforsch. 53, 569–608 (1961).
—: Some observations on the fine structure of planarian protonephridia and gastrodermal phagocytes. Z. Zellforsch. 53, 609–628 (1961).
Roth, T. F., and K. R. Porter: Yolk protein uptake in the oocyte of the mosquito Aedes aegypti, L. J. Cell Biol. 20, 313–332 (1964).
Wetzel, B. K.: Contributions to the cytology of Dugesia tigrina (Turbellaria) protonephridia. Fifth internat. congr. for electron microscopy Q 10 1962.
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This investigation was supported by NIH Pre-doctoral Training Grant 5T1 GM 723-07.
The author is grateful for the interest and guidance of Dr. Orin M. Lofthus and Dr. David B. Slautterback; and is pleased to acknowledge the generous support of undergraduate research by the President and Fellows of Carleton College, Northfield, Minnesota which made possible the initial stages of this work.
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McKanna, J.A. Fine structure of the protonephridial system in planaria. Z. Zellforsch. 92, 524–535 (1968). https://doi.org/10.1007/BF00336663
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DOI: https://doi.org/10.1007/BF00336663