Dr. Murai Éva - Gubányi András szerk.: Parasitologia Hungarica 27. (Budapest, 1994)

and Kovács-Gayer 1986b, Yokoyama et al. 1990). The second phase of the development of parasites belonging to this type takes place in the ureter and urinary bladder in a coelozoic manner. The secondary cells, which in most cases already contain tertiary and quaternary cells at that stage, leave the epithelial cells, change into small plasmodia and form 2-10 spores. In the plasmodium the tertiary cells represent the sporoblasts while the quaternary cells correspond to the nuclei of future spores. The tissue specificity of Hoferellus-type myxosporeans is determined by the cell type in which intracellular development takes place. Usually they can be considered organspecific parasites, although certain Chloromyxum and Myxidium species are likely to be capable of developing in both the kidney and the liver (Dyková et al. 1987). The development of Myxidium lieberkuehni as outlined by Lorn et al. (1989) can be considered a special form of coelozoic development, in the same way as that of Chloromyxum inexpectatum described by Baska (1990,1993) from the renal glomeruli where the plasmodia form a xenoma with the glomerular epithelium. Sphaerospora-type development This type of development (Fig. 4) is characteristic of Leptotheca and Ceratomyxa species, in addition to the numerous representatives of the genus Sphaerospora. For a long time, Sphaerospora-iype development was known to consist of only two blood stages and one renal, or occasionally epithelial, stage (Csaba 1976, Lom et al. 1983, Csaba et al. 1984, Molnár and Kovács-Gayer 1986c, Baska and Molnár 1988). Recently, Voronin (1993) has demonstrated that the development of also these parasites includes an intracellular stage which precedes the blood stages. Thus, in the same way as with other myxosporeans, development continues intracellularly after the invading Actinosporea sporoplasms have gotten to the species-determined site of colonization. The first developmental stage of Sphaerospora renicola establishes itself in the endothelium. By internal cleavage, the trophozoite getting into the blood (C-protozoan, UBO) gives rise to a secondary cell which then divides into eight other secondary cells. Subsequently, tertiary cells develop within the secondary cells. After the disruption of the primary cell, the secondary cells, together with the tertiary cells included by them, may initiate another cycle of 8. After a certain time, from the tertiary cells a second blood stage (K-protozoan) develops, in which about 40 secondary and 2-2 quaternary cells arise by internal cleavage. The nucleus of secondary cells transported by the blood stream to the renal glomeruli and getting, through the latter, into the convoluted tubules corresponds to the nucleus of pseudoplasmodia. The tertiary cells develop into a spore each. In my opinion the pseudoplasmodium is a form analogous with the pansporoblast. The development of the PKX organism, which is probably a parasite of Sphaerospora nature and the causative agent of proliferative kidney disease of salmonids, is somewhat different but similar in its tendency. The second blood stages (K-protozoans) that accompany the circulating primary blood stages and get jammed in the swimbladder capillaries, in the choroid of the eye and in the renal parenchyma are described by many researchers studying Sphaerospora-type development as swimbladder etc. stages, while actually they are blood stages occurring in the capillaries of