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The parasitic system ixodid tick (parasite)—vertebrate animal (host) is relatively stable in space and time. Equilibrium state in the system is maintained at the low levels of the hosts' infection and moderate intensity of their immunity. Parasite sensitizes the host's organism at the stage of feeding on antigens of its saliva and the host develops different degrees of resistance preventing the subsequent individuals of ticks from normal feeding. Antitick immunity is species specific. Its intensity is defined by the species belonging of the parasite and host, intensity and intervals between infections, availability of "anti-immune mechanisms" in tick and by many other factors, which are realized at the feeding stage. Regulation of the number of ticks, depending on their abundance in the host's population, is attained due to the oversparse, close to negative binomial distribution on hosts. This mechanism functions on the principle of feedback, so that at the excessive number of the parasite some individuals in the host's population, which are especially subjected to infection, do not cope with parasitic burden and die. However, ticks, which failed to finish their feening and represent a disproportionately great part of the whole parasite's population, die together with them and the parasitic system quickly restores its stability. In anthropocoenoses and ecosystems at different stages of anthropogenic transformation mutual regulation mechanisms of the parasite and host number break down. As a consequence, extremely high rises in the number of ticks and epizooties of agricultural animals associated with them can occur.

The new subgenus Sternalloptes Mironov subgen. n. is erected in the genus Alloptes. The members of this subgenus are specific parasites of the infraorder Lari birds. The main morphological characters which differ this subgenus from other ones of the genus Alloptes are as follows: absence of the setae d3 in both sexes, lateral margin of opistosomal lobes with 2 setae (l4, рае) in males, absence of setae l4, рае, pai in females. Three new species of the subgenus Sternalloptes are described from two species of terns living on the north coast of the Black Sea: Alloptes (Sternalloptes) niloticus sp. n. from the gull-billed tern Gelochelidon nilotica, A. (S.) thalassei sp. n. and A. (S.) cribripes sp. n. from the Sandwich tern Thalasseus sandvicensis.

Studies on the Siberian jerboa Allactaga sibirica from the Issyk-Kul Lake region and Inner Tien-Shan have revealed a complex consisting of 47 species of parasitic arthropods belonging to four orders: Acariformes, Parasitiformes, Anoplura and Siphonaptera. In the Issyk-Kul Lake region the following species of this complex were most abundant: Androlaelaps semidesertus — abundance index (AI 73.7%), Mesopsylla tuschkan kochkor (AI 52.3%), Ophtalmopsylla volgensis (AI 44.8%); in Inner Tien-Shan Dipolaelaps ubsunuris (AI 88.7%) and Amphipsylla primaris (AI 83.2%). The Siberian jerboa has close host-parasite relationships with the mites Cheyletus allactaga, Radfordia (Austromyobia) allactaga and the louse Eulinognathus allactagae. Index of similarity between the ectoparasite faunas of Siberian jerboa in the Issyk-Kul Lake region and Inner Tien-Shan amounted to 24.3%.

The analysis of morphological and functional peculiarities of sporo- and merozoites as disseminative stages of the sporozoan life-cycle is given. Penetration of parasites into the host's cells is a complex multistepped process very similar to the induced but not completed phagocytosis. As a result of that process the formation of the integrated cell system, which consists of the host's cell and the unicellular parasite takes place.

Development of microhemipopulation of Ph. rhionica rediae in the fresh-water snails Melanopsis praemorsa spontaneously infected with several species of trematode parthenites has been studied. In snails with primary infestation with sporocysts of Cercaria rhionica VIII (Strigeidae) or rediae of Metagonimus yokogawai (Heterophyidae) only the early developmental stages of the Ph. rhionica rediae can be watched. At the same time, the reaction of the host and the "primary" species of parasites is very different in that two cases. The number of strigeid sporocysts slowly decreases and at the end the death of snailhost takes place. In the case of the infection with M. yokogawai rediae the parthenites of that last species only supress the development of Ph. rhionica, but have not been vigorously supressed themselfs. On the contrary in the snails spontaneously infected with sporocysts belonging to the genus Mesostephanus (Cyathocotylidae) (in our experiments have been used two different species) the rediae of Ph. rhionica develope till maturity, but somewhat slower than in the control experiment. Simultaneously with the formation of the redial microhemipopulation the number of Mesostephanus sporocysts slowly decreases. When the first cercariae of Ph. rhionica appear (in 300 days from the begining of the experiment), the cyathocotylid sporocysts are not revealed in most snails. Thus, in that combination of parasites species one of them has replaced the other.

Fat-acidic content of lysosomal membranes and general lipids in two species of cestodes from cold-blooded and warm-blooded vertebrates has been studied. It has been shown that in Eubothrium crassum quantitative differences between fat-acidic spectra of lysosomal membranes and general lipids are negligible and in Diphyllobothrium dendriticum the saturation degree of lipids of membranes in higher as compared to that of general ones. It can be expected that in parasites, whose developmental cycle is connected with a change of hosts that have different body temperature, there evolved preadaptive mechanisms of fat-acidic spectra of lipids to thermal conditions of the environment in which helminth has to develop.

It has been established that bream becomes infected with the cestode C. laticeps when reaching body length over 160 mm and individuals over 340 mm are 100% infected. Seasonal studies on the distribution of C. laticeps in the host's population have shown that mature helminths are encountered within the whole year. Data on the changes in the parasite's population structure as well as the replenishment-residue ratio within different periods of the year are given. Population-genetic studies have shown that at the initial stage of the parasite inflow (fish length 160 to 250 mm) helminths infect those host individuals that are characterized by a high stability of development. When there is no inflow of a new generation of parasites, fishes possessing a more balanced genotype are infected with a lesser number of helminths than individuals having deviations in the stability of development. In the period of an active inflow of helminths individuals with high stability are infected with a greater number of parasites than those having deviations in the stability of development. The paper considers the mechanism of population-genetic interrelations in this parasitic system.

The helminth fauna of 24 kulans from Askanya-Nova and Badkhyz was studied. 42 species of helminths were found, 34 of which belong to strongylids. The helminth species composition of kulan is similar to that of other species of horses. This is a result of an intensive parasite exchange in the historical past when numerous populations of different Equidae species made long seasonal migrations over steppe inter-river lands of Asia and grazed for some time on common pastures.

The paper reports the results of studies on Microsporidia from the bloodsucking mosquito Aedes cataphylla for the period from 1974 undertaken in the Kiev and Chernigov regions of the Ukraine. A new species, Amblyospora cataphyllus sp. n., is described from larvae of the mosquito. Living spores oval or elongate-oval, 6.3—7.5X4.5—5.0 (most commonly 6.8X4.8) µm, fixed spores oval, 5.6—6.9X3.8—4.8 µm. Mucocalyx becomes distinct around spores in 10 to 15 days after the preparation is made. Spontaneously ejected polar tube 125 µm long. Exospore smooth or undulate, 170 to 310 nm thick, endospore 60 to 160 nm. Polaroplast elongated and curved, its 1/3 is composed of closely situated plates and 2/3 of more widely arranged ones. Polar tube anisophyllous, forms 18 to 20 spires in a spore, of which 3 to 5 spires form basal area and 14 to 16 form distal area (of them 1—2 most thick spires form intermediate area). Nucleus large, in a shape of half-ring. In living spores posterior vacuole crescentic, in fixed ones it is strongly deformed together with hind pole of spores. Sporogony of Microsporidia takes place in larvae of mosquitoes of both sexes. Infection extensiveness of IV stage larvae is 10%.

Blood-sucking midges were collected from cow in the first half of the May to July season during two years by means of the animal-baited trap method. Eleven species were recorded. Culicoides obsoletus, C. pallidicornis, C. punctatus, C. grisescens appeared to be common species.

The present investigation shows that the infection of the first year carps with Bothriocephalus opsariichthydis and Khawia sinensis depends on the fish genotype. It has been established that individuals falling behind in their growth are more heavily infected with Bothriocephalus while the largest individuals are more heavily infected with Khawia. By means of genetic marking the differences in the infection with the above cestodes were found to have a common mechanism consisting in the different growth rate of the first year fishes. It has been noted that fishes slowly growing within a season or arresting their growth during the infection period are given to a heavier infection.

The paper describes the basic proteins of chromatin of Digramma interrupta plerocercoids (Cestoda) and the nucleus isolation method. When extracting chromatin by 5% perchloric acid, histon H1 and its isoforms, HMG 14—17 and proteins with molecular mass 35.3, 36.6, 38.8, 45, 66.9, 88.5 kDa go into solution. It is shown that the treatment of nuclei 2M with NaCl results in the rebase of histons H4 and H2A, proteins with molecular mass 35.3, 38.8, 45 and 88.5 kDa from DNA-protein compleces.

The description of a new species of the genus Echinorhynchus — E. theragrae a parasite of Theragra chalcogramma from the Sea of Japan is given.

Data on type specimens of 70 nematode and 5 acanthocephalan species deposited in the Museum of the Laboratory of Helminthology AS with an indication of their generic assignment, collection number and type categories are given. For species recorded for the first time data on type hosts, localities, value of the material and authors of original descriptions are presented.

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