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Reasons of differences in clinical forms of tick-borne encephalitis within certain regions and throughout all area are analysed. It is supposed that the epidemic potential of natural focus depends upon temperature conditions during the winter period.

The general morphology of the internal genital organs in Myobia murismusculi females have been studied by means of light and electron microscopy. It is shown, that their reproductive system is composed of the single ovary, long complex oviduct, cuticular vagina and receptaculum seminis. The apical region of the ovary is formed by the numerous processes of gonadian somatic cells. These cells generate the ovarian sheath and probably take place in oocyte's metabolism. Any nutritive cells in the Myobia ovary are absent. The vitellogenetic oocytes develope in the ovarian pouches like in other trombidiform mites. The oviduct consists of three parts, each of them has a specific ultrastructure and type of secretory product. Two proximal parts of the oviduct produce the egg-shell components, while the third distal part never contains oocytes. It could be suggested that this part produces a special secret onto the oocyte surface to glue the oocytes to the hairs of host.

A revision of chigger mites species, being closely related to Neotrombicula vulgaris (Schluger, 1955), is given. 2 new species are described: N. aideriensis sp. n. from Western Kopetdagh and N. macrovulgaris sp. n. from Western Caucasus. N. aideriensis sp. n. differs from all other species of the vulgaris group by presence of single barb on the lateral seta of palpal tibia in most specimens. This species differs also from N. vulgaris by lesser width of scutum, shorter setae of scutum and idiosoma and by longer legs. N. macrovulgaris sp. n. differs from all other species of the vulgaris group by longer legs, more numerous idiosomal setae and by larger scutum. N. vulgaris is recorded for the first time in Bulgaria, Turkmenistan (Western Kopetdagh) and Krasnodar Territory, N. baschkirica Kudryashova, 1998 — in Chuvashiya, Kirov Province, Komi Republic and Tyumen Province, N. kharadovi Kudryashova, 1998 — in Russia (Altai Territory) and in Karaganda Province (Kazakhstan). The latter species is reported from several new hosts. Variation of morphometric parameters in the vulgaris group are investigated by the methods of multivariate analysis, the pattern of correlations between them is shown. A complex of diagnostic features in the group is revised. Discriminant functions produced by the computer program DIADIS (A. L. Lobanov, ZI RAS) allows to determine confidently representatives of the vulgaris group. Ecogeographical component of intraspecific variability and character variance at the specific level is revealed in vulgaris group. N. macrovulgaris characterized by the largest scutum, numerous setae and long legs was found in the most rigorous, cold and damp climate (alpine zone of Western Caucasus). On the other hand, N. kharadovi, wich have the most fine scutum and shortest setae, inhabits rather dry and warm Middle Asia and neighbouring territories. The sample of N. vulgaris collected in the steppe part of Stavropol Territory differed from the material collected in mountain forests of Western Caucasus by low values of the most part of measurements. N. kharadovi samples from plains of Middle Asia differed from samples of this species collected in Western Pamirs, Central Kazakhstan and Altay Territory by more fine scutum and shorter setae.

The formation of parasite fauna in the european smelt Osmerus eperlanus (L.) accidentally introduced into the Sjamozero Lake ecosystem (South Karelia) have been analysed. The data for the study was obtained during the period of 1969—1996. It is found out, that the parasite species diversity developed from 3-4 species in the beginning of the study up to 17 species in 1996. The parasite fauna of the european smelt evolved from the species with a compound development cycle (Camallanus, Diplostomum, Ichthyocotylurus) to the species with a direct (Trichodina, Capriniana, Glugea). At present the smelt parasite fauna is mainly represented by species haying a wide range of hosts and parasitizing on many fish species inhabiting this water ecosystem.

A new genus Brachylepis gen. n. hymenolepididean cestodes associated with common shrews (Sorex) in Siberia and Russian Far East is created. These genus includes three species removed from the genus Mathevolepis: Brachylepis morosovi (Karpenko, 1994) comb. n. (type species), B. sorextscherskii (Morosov, 1957) comb. n., and B. triovaria (Karpenko, 1990) comb. n. The new genus is characterized by the gradual strobila with a little number of segments, unarmed scolex with apical glandular organ, by lack of internal seminal vesicle and differential seminal receptacle, by form of uterus as horse shoe in young worms and buble-like in mature worms. A tendency of inverse proportional dependence between the number of uterus segments in the strobila and the number of hexacanths in the uterus has been noticed. The table of differential characters for the species of the genus Brachylepis is proposed.

The subfamily Entobdellinae consists of 2 genera and 10 species. Diagnoses for the subfamily and genera, list of species with synonymy, hosts and location are provided.

The list of helminth parasites of the herring gull Larus argentcitus from the Baikal Lake includes 57 species, among them 24 species are recorded for the first time. It is shown, that main subpopulations of the herring gull in different regions of the Baikal Lake are distinguished by the species composition of the helminth fauna, infection rate of parasites and structure of helminth communities.

During the parasitological research of fishes in the Lake Superior (USA) in August — September of 1994, an infection of blood in sculpins (Cottus ricei Nelson, C. cognatus Richardson) with trypanosomes was recorded for the first time. The description of three morphological groups of the genus Trypanosoma is provided: Trypanosoma sp. I from blood of C. ricei, Trypanosoma sp. II and Trypanosoma sp. III from blood of C. cognatus.

Among females and larvae of mosquitoes collected in 1969, 1981—1984 in the area of the Sayano-Shushenskaya hydro-electric power station (140 km up the Yenisei river from the Abakan city) 5 genera and 30 species were recorded. Based on recent collections and reference data (Gornostaeva e. a., 1969; Gornostaeva, Danilov, 1986) the fauna of the region in question includes 31 species of mosquitoes (Anopheles — 1, Culiseta — 2, Coquillettidia — 1, Aedes — 22, Culex — 5).

The paper displays the results of faunistic study of nematodes and proboscis worms, parasites of fishes, in basins of the Dvina river, Mesen river and Pechora river. 18 nematode species and 7 proboscis worm species were recorded in the first basin, 11 and 7 species in the second basin, 8 and 4 species in the third basin. Total number of parasite species in the region examined: 21 nematode species and 9 proboscis worm species.

Adult females of the Philonema sibirica from the baical grayling Thymallus arcticus baicalensis are described for the first time. Some morphological peculiarities are recovered in a comparison to original description.

Summary is absent.