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Vital schemes (according to Beklemishev, 1942, 1945, 1956) of initial forms determine the possibility of their transition to parasitic mode of life and the way of formation of parasitism. On the example of lower and higher Diptera the role of initial trophic behaviour in the evolution of parasitism is shown. When passing to exploitation of vertebrate animals lower Diptera preserve in their behaviour typical traits of predators-entomophags. When passing to muco-and haematophagy higher Diptera preserve the main behavoristic features of saprophags that results in an increasingly close relations with the host. Changes in the host—parasite relationships involve the necessity of agents' adaptations to a new system of relations of their hosts. On the example of nematodes of the order Spirurida there was traced the role of the evolution of trophic behaviour of vectors, namely higher Diptera, in the evolution of the vital scheme of agents.

Trophic relations between ground beetles and ixodid ticks were studied by serological method. Most close food relations were observed in four species of the genus Pterostichus. The greatest number of positive reactions were recorded in P. aethiops (23.5—43.3%). 14.3—20.7%, 9.3— 18.5%, 14.5—15.4% of P. niger, P. melanarius and P. oblongopunctatus respectively took part in the feeding on ticks. On the basis of obtained positive reactions it was concluded that encounters of predators (ground beetles) and preys (ixodid ticks) take place under natural conditions. The beetles can play a part of biological regulators of the abundance of ticks.

Three new species are described: Pteronyssoides pastoris sp. n. from rose-coloured starling Pastor roseus (L.) (type host) and from gray starling Spodiopsar cineraceus (Temm.), Pteronyssus yungipicinus sp. n. from lesser sharpwinged woodpecker Yungipicus kizuki (Temm.), Hemifreyana kurbanovae sp. n. from white-tailed plower Vanellochettusia leucura (Licht.). A brief review of the literature on Avenzoariidae of the USSR is given.

The effect of some ecological factors on the infection of birds with blood Protozoa was studied. Most favourable conditions for circulation of Haemoproteidae on the Kurish Spit were recorded in July. The possibility of the infection of young small passerine birds from the first broods with Haemoproteidae is most high first of all at the expense of their longer stay in the nesting territory in the period of the active transport of parasites. The presence of Leucocytozoidae in Kurish populations is explained mainly by the distribution of birds. The registration of Leucocytozoidae from birds on the Kurish Spit in spring and autumn is the result of the flight of extensively infected northern populations. It is noted that a constant change in the populational composition of the ornithofauna during seasonal migrations should be taken into account when studying the parasites of wild birds. Otherwise the characteristic features of the circulation of parasites in the region in question can be distorted as a result of the overlap of data on the infection of birds of different populations. The dependence of the infection on sex and size of birds — hosts and the role of the nesting period in the distribution of some Haemosporidia are analysed.

The new species Blastocrithidia miridarum sp. n. is described from murid buds (the fam. Muridae) collected in the North-West of the USSR. The laboratory culture was obtained on Liquid and dense nutrient media. The problems of cultivation, morphology of cells in the host's gut and in liquid nutrient medium as well as the structure of colonies on the dense nutrient medium are discussed.

Four-year summer observations have shown that G. takedai distribution in Salmonidae of Sakhalin is limited by the rivers entering the Aniva Bay. Maximum infection of pink salmon (Oncorhynchus gorbuscha) amounts to 70—100%, that of masu salmon (Oncorhynchus masou) to 9.0—45.6% and was recorded in September. Dynamics and possible ways of infection are discussed.

Glandular formations in cercariae of six species belonging to different families, Cryptocotyle lingua (Creplin, 1825) Lühe, 1899 (Heterophyidae), Podocotyle atomon (Rudolphi, 1802) Odhner, 1905 (Opecoelidae), Mesostephanus appendiculatus (Ciurea, 1916) Lutz, 1935 (Cyathocotylidae), Haplometra cylindracea (Zeder, 1800) Loos, 1899 (Plagiorchiidae), Cercaria ubiquita Lebour, 1911 (Microphalidae), Bucephalus polymorphus Baer, 1827 (Bucephalidae), are studied. Differences in morphology, topography, chemical composition of the secretion of glandular formations in species belonging to different systematic groups are shown. The question of a further study of glandular formations in trematodes is discussed.

When studying helminth fauna of Orthotomicus laricis Fabr. on larch in the Magadan region there was found a new nematode species, Parasitylenchus klimenkorum sp. n., which differs from other species of the genus in the shape of spicules of parasitic males. In larvae and pupae of this bark beetle nematodes are localized in the abdominal cavity; in imagos they penetrate the thorax, head, coxae and even femurs of the legs. The development of the parasite proceeds with an alternation of two gamogenetic generations. Karyogamically inseminated females infect larvae of bark beetles, reach maturity in pupae and begin to produce progeny. In imago of the host males and females of the following, fully parasitic generation become mature. Larvae develop to the 4th stage and during the reproduction of the host leave it through the gut. The copulation of males and females of partially free-living generation takes place in passages, after that females become infectious and males die. Study of the life cycle of P. klimenkorum confirms the role of biological character of the development with an alternation of two bisexual generations in the diagnostics of the genus Parasitylenchus.

The paper describes the flight periods and dynamics of abundance of horse botflies, life span of females and males, effect of environmental factors on the activity of flies and their behaviour, potential fecundity of different species of botflies, duration of embryonal development, preservation of viability of larvae in egg membranes, localization of different stages of botflies in the host, and methods of their control.

The development of Cephaloidophora pacifica Avdeev in liver diverticles of Euphausia superba, unlike the gastrointestinal tract, reaches only the stage of gametocyte. The paper considers the reasons which do not allow Sporozoa to accomplish sexual process in this organ.

Electron microscopy study of sporogenesis in Kudoa quadratum has been made. The following peculiarities in sporogenesis of the species were noted: two-cellular sporoplasm, possible development of spore without pansporoblast formation. The question of the existence of heterogamy in Myxosporidia or acceleration of trophozoite development is being discussed.

Experiments were conducted on crossed infection of the specific intermediate host of Opistorchis, molluscs of Bithynia inflata from different and remote populations, with eggs of O. felineus from different nidi of the desease. The strains of the agent were found to be heterogenous that is expressed in different degree of compatibility with the intermediate host.

The dependence of the total number of larvae (potential fecundity) on the body length of females of nematodes was investigated. The reliable differences between indices of fecundity of C. lacustris in lakes with different trophic levels were noted.

The new genus Crenatobronema gen. nov. is erected in the family Spinitectidae with the type species C. guentheri (Baylis, 1929) comb. nov. Description and figures of adults and larval forms of the nematodes are given.

Pathotylenchus gen. n. is erected for a group of species of the subfamily Merliniinae which have 6 lines in the lateral field and stylet longer than 60 µ. Two new species of ectoparasitic nematodes from rhizosphere of Coniferales are erected. Geocenamus patternus sp. n. differs from other species of the genus in the longitudinal striation of the cuticle along the whole length of the body. Pathotylenchus nurserus sp. n. as distinct from the close species P. kirjanevae has a cylindrical tail with a widely rounded annular termination and a longer stylet as compared to P. superbus.

Summary is absent.