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Study of the apron in 9 species of the genus Dermacentor from the fauna of the USSR has revealed differences in its structure. The subgenus Dermacentor (s. str.) differs from two other subgenera both in the shape of the apron itself and in the shape of the postgenital sclerite and setae of perigenital area. Close species within each of two other subgenera differ in apron proportion, shape and size of denticles along its hind edge, and sometimes in their number. In spite of the statistically reliable interspecific differences in apron structure a wide range of individual variability of some details and geographical specificity of samples from various places of the area were observed in species with a vast area.

The ixodid ticks Hyalomma asiaticum, H. anatolicum, Dermacentor niveus were infected experimentally with Karsha virus. The virus replication has been proved to occur in the tick's organism. The titre of the virus grows gradually in infected ticks. Entering the tick's gut during its feeding virus particles penetrate into the gut walls where primary multiplication and accumulation of the virus take place.

The reaction of males of Aedes diantaeus to different auditory stimuli was studied in natural environment during swarming and under laboratory conditions. The males were attracted by 250—420 Hz that corresponds to the main frequencies of flight tones of sympatric females and the range of sensitivity of male Johnston's organs. Behavioural data show that in natural environment swarming males are attracted by flying conspecific and heterospecific females rather than by dead or immobilized females. Contact with heterospecific females always ended in parting of mosquitoes while contact with cospecific females resulted in pairing. Thus, swarming males of Aedes diantaeus localize females by their flight tones but recognize the females of their own species in contact.

3143 fleas belonging to 22 species were collected from 4704 small mammals and 29 nests of common vole on the territory of the Moscow State University agrobiostation "Chashnikovo" (45 km southward from Moscow) in the period of 1965 to 1976. Redbacked vole, common field mouse, common shrew, common vole, and pygmy shrew and of fleas the species C. penicilliger, C. turbidus, Ct. agyrtes, Ct. uncinatus, P. soricis were dominant. An adaptation of mass species of fleas to definite species of warm-blooded hosts was found out. The decrease ofjthe abundance and occurrence indices of fleas with increasing number of small mammals was noted. Some fleas of hair as well as fleas parasitizing small mammals during cold time of the year stay on dead animals for most long periods.

On the basis of the survey of histological preparations of healthy and Polypodium-infected oocytes of acipenserids caught in the Ural cases of parasitism of Polypodium in Huso huso and Acipenser nudiventris are recorded. The forms of the parasite in the oocytes of these species as well as those of Acipenser stellatus are described for the first time. The developmental stages of Polypodium are precisely coupled with stages of oogenesis of its host. Stolons with inverted cell layers occur only in immature females while stolons with a normal position of germ layers in maturing hosts. An early stage of infection, a binucleate cell, has been found in a junior generation of oocytes in A. nudiventris. A similar coordination of the life cycle of the parasite with stages of the sexual cycle of the host, similar reactions of the oocyte to the presence of the parasite, as well as similar sizes of the cnidocysts of Polypodium occuring in oocytes of the three acipenserid species suggest that Polypodium from all Ural acipenserids belong to a single species, P. hydriforme, that occurs in the Volga.

Morphology of Bivaginagyrus obscurus from Pseudorasbora is described. B. obscurus differs from species of the genus Dacfylogyrus by 2 vaginae, shape of median hooks, seat of gill filament and length of additional ventral bar. Morphology of Silurodiscoides infundibulavagina and some other species of this genus parasitic on Parasilurus asotus is described. The morphology of Pseudoancylodisciodes from Pseudobagrus fulvidraco is characterized by 2 ventral bars and peculiar seminal vesicle. Morphology of Bychowskyella pseudobagri from Pseudobagrus fulvidraco is described. The testis in this type species is located more ventrally than the ovary.

5 species of monogeneans are known at present whose egg bundles are usually attached to the opisthohaptor of the parent worm by long stalks. This, apparently, can be regarded as a phenomen of a peculiar parental care.

In three species of gastropods from the Kanino-Kolguev shoal-water the daughter sporocysts of the genus Microphallus and the genus Atriotrema containing formed metacercariae were found. Larvae of Margarites groenlandicus are identified as Metacercariae margaritae-groenlandicus 1 Sannia et James, 1977 while those from Cryptonatica clausa and Buccinum maltzani are new forms; Metacercaria cryptonatica-clausa and Atriotrema sp. Some morphological characteristics of metacercaria found and their differential diagnosis with relative forms are given.

Results of studies of differences in the infection rate of natural populations of Bithynia inflata with trematodes (including Opisthorchis felineus) in the nidi of opisthorchiasis in the Sumsk and Chernigov Districts of the Ukrainian SSR and Tomsk District of the RSFSR are given. It has been shown that in the Ukraine over 1/3 of all populations of the specific intermediate host of opisthorchis does not take part in the circulation of the agent due to fundamentally different reasons: resistance to the infection and hyperinfection with parthenites of trematodes.

Electron microscope studies of integuments of cystacanth of P. strumosoides Lundström, 1942 have shown that their architectionics is subject to the general structural pattern of integuments of all acanthocephals studied. Epidermis of studied larvae is characterized by the presence of a thick layer of glycocalyx on the surface of the body, the formation of a system of hypodermal fibres, a peculiar structure of inner part of hypoderm, which is separated into a special "tubular" layer. The above peculiarities provide a longer stay of formed larvae in the intermediate host and favour their infection of the definitive host. The hypodermal structure of the studied cystacanths has a definite similarity with that of the wall of larval cyst of cestodes belonging to the suborder Hymenolepidata.

Manifestation of sexual dimorphism at the preimaginal phase was studied on the laboratory culture of Ixodes persulcatus. It has been found out that larger engorged larvae produce, in general, larger nymphs and smaller larvae produce smaller nymphs. The classification of engorged nymphs into large (over 2.9 mm) and small ones (less than 2.9 mm) has made it possible (with 100% probability) to obtain females from the former and males from the latter. Differences in linear sizes of scutum, gnathosoma and its appendages in male and female nymphs were determined that has made possible the identification of sex in hungry nymphs.

Distinct differences in the intensity and dynamics of the infection with cysts of toxoplasms of law virulent (Czech) strain of brain of mice of three different pure lines and strainless ones differing in the sensitivity to the agent during a chronic period of infection have been noted. In sensitive mice of AKR line the period of formation and growth of cysts as well as the period of their elimination from the brain is longer than in less sensitive ones. In this connection cysts in the brain of these mice turned out to be larger than in the brain of Jess sensitive mice of GC57BR line. Activation of the infection in the brain, revealed microscopically, is observed most commonly in mice of AKR line (40%), more seldom in GG57BR (9.1%) and strainless ones (7.7%) and is not observed at all in resistent BALB/c. Lethality of these mice was by 9 months of infection 87, 40, 41 and 5.3%, respectively. 1—1.5 year after the infection in animals without relapses the infection level of brain was equally low.

Five new species are described as follows: M. haematopterus from gills, fins and skin of Cyprinus carpio haematopterus; M. gibelio from connective tissue of gill filaments, fin rays and kidneys of Carassius auratus gibelio; Myxobolus waleckii from gills of Leuciscus waleckii; Myxobolus junchisi from gills, muscles, kidneys and spleen of Cyprinus carpio haematopterus; M. alacaudatus of Cyprinus carpio haematopterus and Carassius auratus gibelio; Myxobolus divergens carassii from gills, muscles, fins, and cartilaginous tissue of operculim of Carassius auratus gibelio and Cyprinus carpio haematopterus.

Summary is absent.

Summary is absent.