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Cyclic changes of the midgut epithelium were observed in females of 5 ticks species of the genus Ixodes during 7—10 days of feeding. The midgut epithelium of unfed females is represented by the digestive cells of nymphal phase and stem cells. The digestive cells of nymphal phase are functional during 1.5—2 days after attachment of the tick, and then, after the tearing away they go into the gut lumen. The secretorycells substitute the digestive cells of nymphal phase and finish their growth during the 4—4.5 days. Secretion of digestive enzymes is performed by the holocrine type with tearing away a whole cell. Intracellular digestion takes place in the digestive cells of four consequent generations. The secretory and digestive cells form a peritrophic matrix on their surface. The presence of peritrophic matrix gives an evidence the maturity and functional activity of the secretory and digestive cells. We suggest, that the peritrophic matrix takes part in intracellular digestion, namely in the process of micropinocytosis. The phagocytosis was not found in the ticks investigated. Digestion in the midgut lumen is performed by enzymes of the ruptured secretory and digestive cells, that is proved by the haemolysis of erythrocytes in the zone of their contact with these cells. The digestive cells of each generation functioned almost synchronously, with largest difference in starting about 12 hours.

The twelve flea species were revealed on bank voles. Only four of them (Amalaraeus penicillige, Ctenophthalmus uncinatus, Megabothris turbidus, Peromescopsylla bidentata) were abundant in some seasons of the year. Four other species (Ct. agyrtes, Hystrichopsylla talpae, P. silvatica, Rhadinopsylla integella) are the parasites of bank vole too but their numbers were always low in the study areal. The four last species (Amphypsylla rossica, M. walkeri, Doratopsylla dasycnema, Palaeopsylla soricis) are not peculiar to bank vole. They occurs on it occationally from other animals — the voules of Mucrotus and shrews. The most species diversity of fleas on bank vole was observed at the period from August to Oсtober, the least one — in late winter, spring and early summer. The total abundance indices of fleas on the voles (mean number of the insects per host) ranged in different monthes from 0.17 to 5.65. The time of minimum flea numbers was August—September. The peak abundance was reached in springtime (March—April).

Discrete variability of four P. osculatus characteristics descriptive of cestodes' major functional complexes: attachment and trophic-reproduction, was determined. Phenotypic diversity of P. osculatus from 2 samples collected at different stages of the population reproductive period was analysed. Unequal adaptation of phenotypes to the ambient conditions was hypothesised.

The results of analisis in the blood of healthy and ones infected with the plerocercoides Ligula intestinalis bream Abramis brama L. over index common lipids (CL) and them quality content, peroxidation (POL), peroxid gemoliz erythrocytes (PGE), common antioxidant activity (CAA) are displayed. It is plerocercoids L. intestinalis effects points character lipids exchanges. At ones infected individual comparatively with healthy increase of CL, alteration correlation lipids fraction, intensification POL and PGE as well as a decrease of CAA, that negative effects on vital function of the blood.

The effect of gravity and light on vertical distribution of Cryptocotyle concavum (Heterophyidae) and Maritrema subdolum (Microphallidae) cercariae in the water column was experimentally studied. Maximal larvae concentration was found in zones where the highest probability of contact with potential host is considered.

Muscle formation in Intoshia variabili (Orthonectida) has been studied in the course of development of the sexual (free-living) specimen. The muscle system originates in the early embryogenesis as a distinct continuous layer located between the outer cell layer and the inner cell mass. Later this cell layer disintegrates into separate muscle strips. The presence of a distinct muscle system in Orthonectida and the pattern of its development evidences for placing this group into Triploblastica rather than into Diploblastica.

Scoleces of two dilepidid genera, Kowalewskiella Baczynska, 1914 and Himantaurus Spasskaja et Spassky, 1971, were investigated. The rosteilar hooks of both are of davaineoid type, which is quite uncommon for the family. The morphology of their rosteilar apparatus, especially the form of proboscis, differs much. But when the rostellum is retracted, the crown of hooks is folded in the same manner: hooks tips assume anterior direction. The muscular system of rosteilar apparatus and the transformation of scolex in the act of rostellum's retraction of Kowalewskiella finds close analogy in Aploparaksis (family Hymenolepididae s. 1.), and of Himantaurus — in Paradilepis (family Dilepididae). But such morphological and functional resemblance between scoleces of Kowalewskiella and Aploparaksis from one side and of Himantaurus and Paradilepis from another is undoubtedly a result of convergence. The morphological types of rosteilar hooks in these pairs of genera are very different.

Striking resemblance of pathological alterations in the development of insects caused by 1) infection with microsporidia, 2) infection with other parasites, and 3) variety of adverse environmental factors is discussed.

Brought description trematodes Psilotrema acutilostris Oschmarin, 1963 received as a result experimental studying a life cycle. Installed that in conditions of Primorye land a role of intermediate host trematodes execute snailes of Parafossarulus spiridonovi and P. manjuricus. The most further development trematodes goes with formation adolescaria. Adult worms P. acutilostris were growing in the chicken.

New species of the myxosporidian genus Chloromyxum is described from salmonid fishes collected in Karelia, Norway and Finland in 1992—1998.