Dr. Murai Éva szerk.: Parasitologia Hungarica 19. (Budapest, 1986)

and some trophozoites that had got stuck there. In some cases the epithelial cells of the tubules almost completely disappeared, and their presence was indicated only by a small islet containing cell nuclei and trophozites (Fig. 3). The lumen was filled with trophozoites, separated from the renal interstitium only by the basement membrane of the tubule In such cases the basement membrane was thickened and gradually became replaced with connective tissue. In the lumen of the tubules some trophozoites remained compact, but most of them had disintegrated to secondary units. Disruption of the tubular epithelium and release of the trophozoites into the lumen must have started centrally in the Hoferellusinfected area. Therefore, in distal portions of the tubules there still were intracellular Hoferellus trophozoites, although the lumen was already filled with trophozoites released from proximal portions of the tubules (Fig. 4). However, signs indicative of degeneration were already visible on the cell membrane of the distal portions as well. In the tubular portion containing remnants of syncytia and cell debris, left over after Hofe rellus infection, proliferation of connective tissue had started from the direction of the peritubular connective tissue (Fig. 5), and fibroblasts accompanied by a few phagocytes penetrated the detritus containing epithelial cell nuclei, cytoplasmic debris, and one or two Hoferel lus trophozoites (Fig. 6). The amorphous mass formed in this way had become surrounded by several layers of connective tissue. Parallel with connective-tissue proliferation, the centrally located debris became concentrated (Fig. 7) and islets formed of epitheloid cells appeared around it. In that stage, infection changed its location and spread to the lumen of the ureter where large numbers of plasmodia formed of trophozoites were seen (Fig. 8). DISCUSSION The present investigations have confirmed the results obtained by MOLNÁR, CSABA and KOVÁCS-GAYER (1986) on the development of H. cyprini. In one of the 12 fish examined, infection was at the stage when intracellular Hoferellus stages get into the lumen of the renal tubules. In the remaining 11 fish this process must have taken place early in January or in the end of December, since in these fish there were only coelozoic developmental stages in the ureter, and infection of the convoluted tubules was indicated by debris-containing foci demarcated by connective tissue, formed in the place of intracellular developmental stages. As it has been shown histologically, in a certain stage of development, usually in January, the intracellular trophozoites of H. cyprini get into the lumen of the renal tubules, into coelozoic position. This is not an active process, i.e. the trophozoites do not migrate into the lumen, but get there due to degeneration of the syncytium formed by the parasites. In histological preparations the areas containing intracellular parasite stages appear spherical or oval in shape. Actually, in the opinion of LOM and DYKOVÁ (1984), they are elongated formations situated along the convoluted tubules. An interesting feature of intracellular infection is that it usually involves only one side of the tubules, and on the other side there frequently are epithelial cells devoid of infection. If in certain portions of the infected area degeneration takes place earlier, in a tubule portions distal to that area intracellular and coelozoic forms will occur simultaneously (Fig. 4). In such a case H. cyprini stages situated in the lumen should not be mistaken for developmental stages of Sphaerospora renicola which differ from H. cyprini both in size and in seasonality. The excretion of trophozoites is soon followed by the destruction of nuclei pushed to the basement membrane of the syncytium-forming cells and of the intact tubular epithelial cells, since connective tissue proliferating from the direction of the basement membrane compresses the remnants of the epithelium and syncytium. Passed-off Hoferellus infection is characterized by foci encapsulated by several layers of connective tissue, similar to those developing in tuberculosis, Ichthyophonus infection, or infection by some other myxosporean. Obviously, DYKOVÁ, LOM and GRUPCHEVA (1983) and LOM and DYKOVÁ (1985) must have seen similar foci. The opinion of the above authors, i. e. that Hoferellus foci represent a blind alley of development, must be due to the fact that