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

where they are expuised into the outworld with the help of macrophages (Fig. 2). The majority of spores, however, get stuck in the macrophage centres of the spleen, liver §*trapiscAnf Fig. 1. Myxobolus-type development. Extrapiscine development is followed by two intracellular stages, Plasmodium formation and then sporogony and spore dejection. (1) During extrapiscine development, stages of Actinosporea develop in Oligochaeta intermediate hosts. (2) Actinosporeans floating in the water infect the fish through the skin. (3) The sporoplasms released from actinosporeans colonize the epithelial cells, undergo a limited number of divisions, then migrate, probably along the nerve tracts, to a site specific of Plasmodium formation. (4) Sporoplasms (trophozoites) that have invaded a host cell specific of the development of the given species start to grow by multiple endogenous divisions and form a plasmodium. (5) In large cells the plasmodium develops intracellular^/, while small cells become disrupted and the plasmodium continues its development extracellularly. As a result of serial divisions, vegetative nuclei and generative cells appear within the plasmodium. (6) The plasmodium is surrounded by a cell layer, so-called "cyst wall", formed of host cells. These cells are of the same type as those in which the parasite commenced its development. Internal cleavage of the generative cells gives rise to pansporoblasts. (7) The number of sporoblasts (1-2 or more) developing in the pansporoblast is characteristic of the given species. From each sporoblast a spore develops. (8) After the formation of the spore the pansporoblasts undergo necrosis, the cyst wall bursts, and from the plasmodia developing near the surface the spores get into the outworld and continue their development in oligochaetes.