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Additions to the method of estimating the absolute and relative numbers of the pasture ticks in test areas are proposed. Additions take in attention the influence of ticks immigrating to the test area in dependence upon the isolation rate of that area. It has been stated that in the period 1987—1991 the mean relative number of I. persulcatus (mean tick number per 1 flag-kilometer of three decades) was 48, 27, 57, 29 and 38; the absolute tick number on test area (tick number per 1 hectar) — 1590, 691, 1194, 641 and 668; the absolute tick number near the field station — 1402, 647, 1496, 668 and 1108 respectively.

It has been shown by means of light and electronic microscopy, that the yellow body formation in Stomoxys calcitrans is connected with the autolysis of follicular epithelium and the further accumulation of its remains. It takes about 2 days and does not depend upon nutritional conditions of flies. New formed yellow bodies of the first and second gonotrophic cycle are usually colourless structures with some PAS-positive inclusions, which correspond to the large telolysosomes on ultrastructural level. They lose such inclusions later and accumulate the yellow pigment in their content. Yellow body of the last oviposition always lies in close contact with the previous one, because of the continuity of the egg development in flies. Then they are consolidated in a single mass and enlarged with successive oviposition as a big and dence body. Therefore, there is no possibility to count the exact number of ovipositions in Stomoxys calcitrans basing on the number of ovarian yellow bodies. So, it is proposed to take into account all possible combinations of the follicular relics, such as dilatations, new and old yellow bodies.

Two new species of Neotrombicula Hirst, 1925 are described from Western Kopetdagh. N. orestias sp. n. is similar to N. nagayoi (Sasa e. a., 1950) and differs from it by barbed lateral seta of palpal tibia, presence of only 6 setae in first dorsal row, another configuration of 2—4 dorsal rows, sharp twist of posterior margin of the scutum, more thin dorsal setae and its barbs, strongly barbed sensillae and by some measurable characters. N. agriotricha sp. n. is similar to N. minuta (Schluger, 1966) and differs from it by barbed lateral seta of palpal tibia, another fD, significantly longer barbs of scutal and dorsal setae, more short and numerous barbs of sensillae and longer setae of idiosoma. Both new species resemble one another by specific arrangement of D in 3—4th rows, sitilarly barbed sensillae and D, barbed lateral seta of palpal tibia.

The ultrastructure of the microsporidian primary described as Pleistophora obtusa and transferred later to the genus Microsporidium (Sprague, 1977) has been studied. The most striking feature of its life cycle is the presence of a short intermediate stage between mero-and sporogony. All other development stages possess monocarions. Sporophorous vesicles contain even number of spores (from 4 to 32) resulted from "rosette-like" budding. The walls of the sporophorous vesicle are thin and fragile. The secrete formation of lamellar and tubular structures are abandant inside the vesicles. Exospore consists of two layers. The polar tube has isofilar structure and forms 6—8 coils inside the spore. Polaroplast is separated in two parts altering in the density of lamellae. The parasites are localized mostly in the Daphnia pulex fat body. The size measurements of living spores are 4.3—4.6 X 2.6—3 micrometers. The comparative analysis of polysporal microsporidia genera) of the subclass Nosematida is given. The peculiarities of the nuclear structure of different development stages as well as other ultrastructural features allow us to establish new genus Larssonia. The new combination Larssonia obtusa comb. n. is given for the former Microsporidium obtusa. The survey of polysporal species of the genus Microsporidium from Cladocera and their comparision with L. obtusa lead to the conclusion that Microsporidium sp. III 10 Loubes, 1979 seems also to belong to the genus Larssonia.

The mass infection of larvae and youngsters of carp fishes with the peritrichoid Ambiphrya ameiuri has been recorded in natural condition in the Rybinsk water reservoir. The uneven localisation of ambiphryans on the body surface has been observed on the hosts Blicca bjorkna and Abramis brama. Most high density of parasites was on the breast, back and 'tail fins. The morphological variability of ambiphryans in dependence upon their localisation on the fish body has been observed. Detailes being significant for the taxonomy have been studied by mean of the scan electron microscope. It has been found, that the scopulae (greatly developed attaching organ of A. ameiuri) in cases of heavy infection cover about 50—60% of the skin epithelium of fish larvae. In these cases the significant part of skin epithelium, which performs the respiratory function, is excludes of the active oxygen supply that cause the illness and death of young fishes.

One new species of parasitic copepod Enteropsis arcticus sp. n. (Ascidicolidae) is described from the ascidian hosts Molgula cirtina, M. arctica, Ascidia prunum and Cheliosoma makeyanum collected in the Bay Chupa of Kandalaksha Gulf (White Sea).

The main purpose of the present study is the investigation of relationships of Pneumocystes carinii with the organism of white rat Wistar, which is natural carrier of this parasite. The serie of experiments has shown that the immunosupressor Tricort-40 (corticosteroid of prolonged activity) in a short time reactivates the pneumocyst infection. The parasites have been observed in a great number in the lungs and rarely in the liver. The reactivation and dissemination of the pneumocyst infection have been achieved constantly and with great expression by the combinative immunosupression of rats, by the medicamental immunosupression (injection of T-40) and biological one (infection with amastigotes Leischmania infantum). The developing mixt-infection (with pneumocysts and leischmania) could be the basis for the parasitocenological relationships.

Topographic anatomy of the nervous systems of the trematodes Azygia lucii and Phyllodistomum angulatum was studied by the histochemical method of cholinesterase detection. The cholinergic part of the nervous system of A. lucii is represented by the brain, the ventral, dorsal and lateral longitudinal cords, by rather long complementary anterior branch of the ventral cord, and by very short anterior branch of the dorsal cord. All cords are connected with numerous commissures. In the anterior region of the body, between the brain and the ventral sucker there are distributed 9 ring commissures. Behind the ventral sucker there has been revealed up to 18 commissures, 10 of wich are ring ones. The regularity of the distribution of commissures is disturbed only in the region of the ventral sucker. The nervous system of such type can be regarded as a regular frequent orthogon. In Ph. angulatum has been revealed another type of the nervous system — an uneven orthogon. It is represented by the brain, 3 pairs of longitudinal nerve cords, small complementary anterior branches of ventral and dorsal cords, 5 ring commissure between the oral — and ventral suckers and one ventral commissure behind the ventral sucker. The origin of regular frequent ortogon in A. lucii and the irregular orthogon in Ph. angulatum is explaned by certain morphological peculiarities of their structure: the body shape, musculature development and the reprodactive system localization. The morphological diversity being a characteristic for the trematod nervous system allows to relate them with Neorhabdocoela suborder Typhloplanoida.

Some aspects of the evolution of ectoparasites are considered.

Basing on materials collected from the fishes of the south part of the Indian and Pacific oceans, 2 new species of trematodes are described: Liliaoralis cataluphi gen. n., sp. n., Steganodermatoides notocanthi sp. n. The diagnosis of the new genus and discrimination are given. The detailed anatomo-morphological descriptions, illustrations and differencial diagnoses are given for each of new species.

In the Maritime Territory of Russia (Far East) the fish Percottus glehni Dybowski was recorded for the first time as the host of the nematode Philomethroides lusiana (Vismanis, 1966). The parasites (young females) were localized in the swelling on the head of the fish.

Summary is absent.

Summary is absent.