Dr. Murai Éva szerk.: Parasitologia Hungarica 23. (Budapest, 1990)

that in external morphology the slender cultured forms are very similar to the metacyclic forms in the leech, while the broader forms resemble the blood forms. The only exceptions are the rounded forms. Despite the smooth surface of the slender or contorted specimens, the cell surface of these forms is undulated by extrusions. They seem to be living and multiplicating but anomalous forms. TEM The first and second types of forms do not differ significantly in fine structure from the bloodstream stages of examined species of the family Trypanosomatiaae. The cell membrane is a dense or less dense single layer, covered by fine filamentous material. Under the membrane the very characteristic single layered structure of subpellicular microtubules can be observed (Fig. 5). In cultivated forms also the "concave" surface of pellicle, opposite to the origin of the preoral ridge, is devoid microtubuli. Nucleus The nucleus is rounded, and sometimes has irregular shape. It possesses a large, characteristic nucleolus which is absent from dividing forms. The nucleus is located centrally. Electron-dense chromatin is visible throughout the nucleoplasma and along two layers. RNA microbodies attach to the outer membrane (Fig. 15). In the dividing stages often only the outer membrane remains and the two daughter nucleoli are covered only by a single separated layer, within the common outer layer of the membrane (Figs 5 and 15). When the two daughter nuclei begin a second cycle of division, four nuclei are located within the original outer membrane (Fig. 16). Peripheral chromatin is in contact with the nuclear membrane. Kinetoplast - mitochondrion The single kinetoplast - mitochondrion complex is situated dorsally and covered with a double-layered membrane. The kinetoplast is elongated in the slender forms, but rounded or elliptical in the rounded ones. The DNA content is composed of an electron-dense network of fine fibres, the mitochondrial part is composed of tubes, ampulla or plate-like cristae. Concentric membrane structure is often observed (Fig. 12). The mitochondrial part is connected with an electron-dense plaque (Figs 11 and 12). Flagella The structure of the flagella corresponds to that of normal blood forms. The two basal bodies lie between the bottom of the flagellar pocket and the kinetoplast (Figs 9, 10 and 11). The basal body is connected to the axosome by a transitional zone. The paraxial rods of the flagella and the central double microtubuli originate at this level. The diameter of the flagellum is reduced to that of the terminal thread. The flagellar pocket of longer forms corresponds to that of the bloodstream forms. The large pocket posteriorly continues in a narrower postflagellar pit. The rounded forms do not have a typical flagellar pocket (Fig. 16). The anterior flagellum emerges from the pocket in the vicinity of preoral ridge. The recurrent flagellum originates posterior to the anterior flagellum, turns posteriorly and attaches to the surface of the cell (Figs 6 and 10).