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By means of hystochemical and electron microscopy methods frontal and uterine glands in four members of caryophyllid cestodes at different stages of their ontogenesis have been studied. Two types of frontal glands were found out; glands of the first type are formed due to specialization of scolex integument and are connected with the protection of worms from the hosts immune effect. Glands of the second type are separated from the integument by cellular contacts. Uterine glands are a modificated wall of the parasite's uterus. The glands secretion provides the protection of eggs during their penetration through the medium of the definitive host's gut.

Ultrastructural organization of embryonal membranes of eggs in 5 species of hymenolepidats belonging to two families (Dilepididae — D. bacilligera, D. tundra and Hymenolepididae — A. raushi, M. microskrjabini, W. pacificum) parasitic at the larval stage in various aquatic invertebrates was studied. An unusual embryophore, a multicomponent structure 10 mkm thick, in D. bacilligera is described. The obtained data on comparative micromorphology of the embryonal membranes testify to the presence of specific peculiarities in their structure and permit to regard them as a complex of cenogenetic structures adapted to concrete conditions of the environment in the broad sense. A connection of fine structure of the embryonal membranes, embryophore above all, with processing of food by intermediate hosts, aquatic invertebrates of various taxonomic groups, is shown.

The structure of scolex in the cestode Nematoparataenia southwelli from mute swan from the Kurish Spit of the Baltic Sea is described. The revision of the genus Nematoparataenia Maplestone, Southwell, 1922 has shown that the species N. brabantiae Cotteleer, Schyns, 1961 and N. skrjabini Mathevossian, Okorokov, 1959 should be considered synonyms of N. southwelli. Genetzinskaya's view (1944) is confirmed concerning the belonging of the genus to the group of davaineata cestodes (Cyclophyllidea, Davaineata).

Helminth fauna of Rana lessonae Cam. and R. arvalis in regions subjected to a strong anthropogenic influence was studied. It is shown that the distribution of two most abundant species of nematodes, Oswaldocruzia filiformis (Goeze) and Cosmocerca ornata (Dujardin), in investigated hosts populations is in keeping with negative binomial distribution.

Identification of serotonin and dophamin in M. salmonis was conducted by means of some fluorometric methods. The presence of negligible amount of a serotoninlike component and substance close in its spectral characteristics to dophamin was shown.

The localization and modes of attachment of Blastocrithidia miridarum trypanosomatids in the intestine of Adelphocoris quadripunctatus were studied at the ultrastructural level. In the hosts' crop the flagellates fill the folds and intercellular space of the epithelium making densely packed masses in the latter. In the midgut B. miridarum are attached by interdigitation of their flagella with microvilli of the epithelial cells. The distal parts of flagella are enlarged and form outgrowthes which favour the anchoring of the flagellates on these cells. In the crop, midgut and rectum B. miridarum are often wedged into masses of extracellular membrane formations or introduce their flagella into the masses of these formations. Rarely an unusual way of attachment of the flagellates to extracellular membrane formations with the help of folded bulges of parasite plasma membrane is observed. In the midgut and rectum of A. guadripunctatus bugs about 5% of B. miridarum form clusters of epimastigotes in which parasites are joined for a long time by a complex flagellum containing several axonemes and paraxial rods. Formation of these clusters contributes to anchoring of the parasites inside their hosts.

Mechanisms of effect of some morphophysiological parameters of cattle (age, colour, weight, skin area, intensity of defensive movements) on the attacking and attaching activity of tabanid flies were studied. Investigations were carried out in the south of the Pskov District in small herds by the method of simultaneous recording of attacking and attaching tabanids on all animals of the herd. It was established that differences in the attaching activity of Haematopota, Tabanus and Hybomitra flies depend mainly on the parameters affecting the efficiency of their attacks and connected with the age of animals, intensity of defensive movements and the host's skin area. The former correlates with the age of cows negatively while the latter positively. Therefore, more tabanids attach themselves to old animals than to young ones. For Chrysops flies the main factor determining their intensity of attachment is the intensity of attacking. When attacking the Chrysops flies show preference to animals of dark colour independent of their age. It is shown that the increase in the attacking intensity results in the decrease of its efficiency and therefore reduces the probability of attachment for each individual.

Materials on occurrence and abundance of 36 species of fleas on 17 species of small mammals are systematized. A great similarity between faunas of ectoparasites of rodents and predators has been shown by means of special indices. The conception of parasitic field is formulated which implies the phenomenon of community of the fauna of plague vectors parasitic on its potential carriers. Some aspects of the formation of parasitic field and its possible effect the epizootic process are considered. It is established that the similarity between the faunas of fleas from different animals is ensured in this region first of all by a wide distribution of specific parasites of gerbils.

Two new spicies of Trypanosoma, T. mikailovi sp. n. and T. ibragimovi sp. n., from the blood of Rana ridibunda Pall. found in the Divichinsky Bay of the Caspian Sea is described.

Two new genera of the lepocreadiid trematodes, Gibsonia gen. n., (type species — G. hastata sp. n.) from Macrourus carinatus Günther, 1878 (Macrouridae), collected in Falkland area, and Muraenolepitrema gen. n. (type species — M. magnatestis sp. n.) from Muraenolepis microps Lönnberg, 1905 (Muraenolepidae), collected in the South Georgia Isl. area, are described. Gibsonia gen. n. differs from all known genera of the family Lepocreadiidae by unusual body shape divided into 2 parts, suctorial formations, great number of glandular cells and musculary bulge of the body sides; it differs from the closely related genus Lepidapedon by separate genital pores. Muraenolepitrema gen. n. differs from Myzoxenus by bursa shape, separate genital pores, lobed shape of genital organs.

The structure of the surfaces of midgut and salivary glands in hungry and engorged females of Hualomma asiaticum was studied by means of scanning electron microscopy. Preparations were fixed in glutaraldehyde osmium and then dehydrated by the critical point method and gold or platinum coating. Different periods of fixation at room temperature or at 4°C did not affect the condition of surface structures of gut and salivary glands.

Fleas of Ctenophthalmus rettigi Rothschild, 1908 (12 females, 12 males) collected in 1980 and 1982 in the North Caucasus in the Levashinsky region of Dagestan not far from the village of Urma were referred by the authors to the nominative subspecies described from Rumania. According to their taxonomic characters fleas of this species, collected in different places of Transcaucasia, are also referred to the nominative subspecies and not to C. rettigi smiti Klein, 1962, as before (Rostigaev, 1967; Tiflov, Skalon, Rostigaev, 1977 and oth.). The ways of distribution of hosts of C. rettigi fleas are suggested.

A new species of Myxosporea Alatospora solomoni from Trachurus mediterraneus is described. Two more species Sphaeromyxa balbiani from Blennius sanguinolentus and Ortholinea divergens from Symphodus roissali are found in the Black sea for the first time.

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