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The material was collected in the Tanysk Inlet and neighbouring regions of the Okhotsk Sea in 1969—1971. 438 animals were examined in spring and 342 — in antumn. 11 species and 4 larval forms were registered. The trematode Phocitrema fusiforme and nematode Terranova decipiens were found only in spring and larvae of Diphyllobothriidae gen. sp. and Terranova sp. — in autumn. A reliable difference in the invasional extensity during these seasons was established from 8 species of helminths.

Compound egg membrane, multilayer walls of the body in the daughter sporocyst, endocyst and aggregate cysts are specific cenogenetic adaptations of Dicrocoeliidae. These cenogeneses provided the increased viability of Dicrocoeliidae during their larval development and promoted their transition to new habitats, adaptation to new hosts.

Two new species of trematodes of the family Microphallidae Travassos, 1920 were found in the Posjet Bay (the Sea of Japan). Cercaria orientalis 6 sp. n. was found in Littorina brevicula and Littorina mandchurica; Cercaria orientalis 7 sp. n. — in Falsicingulcb athera.

An identification and a redescription were made of a species described by Kathariner (1894) as Gyrodactylus medius. The author has added new data to its morphological and metrical variability, to its occurrence and distribution. We believes that G. carpio Kritsky et Mizelle, 1968 is a synonym to the species G. medius.

Studies were carried out of the localization of young and adult cestodes of Hymenolepis nana in the host intestine. It was established that young and adult cestodes change their localization place within a day and display a distinct tendency to forward movement.

The paper presents a description, figures and differential diagnosis of a new nematode species, Neoxysomatium caucasicum sp. n., found in the intestine of slow worms of the Caucasus. The new species differs from N. brevicaudatum (Zeder, 1800), a widely distributed parasite of amphibians and reptiles, slow worms in general, of Europe by the length of spicules, gubernaculum shape, length of vagina and other characters.

Six species of ixodid ticks were recorded from the Leningrad region as follows: Ixodes persulcatus P. Sch., Ixodes ricinus L., Ixodes trianguliceps Bir., Ixodes apronophorus P. Sch., Ixodes lividus Koch and Dermacentor pictus Herm. The first two species are the vectors of tick-borne encephalitis. Many-years observations have shown that I. persulcatus is adapted to elevated moraine hilly, low-lying lake-glacial landscapes and dark-coniferous forests of southern and middle taiga. I. ricinus prefers low-lying lake-glacial and lake landscapes and piny south taiga and small-leaved forests. Each ten days on constant routes calculations of the number of ticks were made. Two types of seasonal changes in I. ricinus activity as well as an autumn pick of I. ricinus nymphal activity were established. The seasonal changes in the life cycle of this tick were found to be associated with the data of indicational phenology.

A study of the peculiarities of the territorial distribution of Dermacentor nuttalli was undertaken in 1972 in the Koibalskaya steppe (Khakass autonomous district). For this purpose D. nuttalli larvae were collected from vegetation on a drag-skin.

Observations were carried out on the destruction rate of blood erythrocytes of Rhombomys opimus Licht. and Gymnodactylus caspius Eichw. in the sand flies Phlebotomus papatasi, Ph. mongolensis, Ph. sergenti, Sergentomyia arpaklensis and S. grekovi at a temperature of 23 to 25° and a relative air humidity of 62 to 68%. It was established that in the Phlebotomus the destruction of blood erythrocytes both of Rhombomys opimus Licht. and Gymnodactylus caspius Eichw. proceeds considerably slower than in the Sergentomyia. Besides, beginning from the end of the 2-nd stage digestion considerable differences were noted in the erythrocytes destruction rate between individuals belonging to the same species. These differences are especially distinct when the material is treated by the dispersion analysis method.

Aedes implicatus Vock., a mosquito species known formerly from North America only, is found in mountain areas of the Amur region (Soviet Far East). The description of its female, male genitalia and larva (IV instar) is given as well as some data on its breeding places and biology. It belongs to early spring species and is rather common but nor abundant. The form of the claspette filament in A. implicatus males found does not differ from that of A. cataphylla, therefore it cannot be used for distinguishing these species as many authors do. For this purpose can be used a prominent finger-like apical lobe and cluster of long and stout setae arising from its dorsal base; these features are absent in A. cataphylla and A. leucomelas, the species close to A. implicatus by male genitalia.

24 species of black flies were recorded from the tundra of southern Yamal. Of them seven species attacked for bloodsucking. A description of their hatching places is given; the effect of weather conditions on the seasonal variations in the number and daily rythm of the activity of black flies is discussed.

According to the author's observations in the lowland, foothill and mountain zones the incidence of sheep infestation with the bot fly accounts to nearly 90%, the average infestation being from 40 to 50 larvae per one animal. The bot fly has two generations. The first generation develops from October to May, the second one — from June to August. The flight on the mountain pastures proceeds exclusively on account of females which fly after the sheep from valleys 40 to 50 km and even more. The I-st stage larvae are localized in the walls of the nasal cavity and in the ethmoid bone where the moulting takes place; the II-nd and III-d stage larvae — in the frontal sinus and partly in the horn base.

The treatment of colonies of the great gerbil (Rhombomys opimus Licht.) with 10% DDT dust from the apparatus of deep dusting (ADD-63) should be regarded as a measure of urgent current antiplague prophylaxis. The evaluation of the effect of desinsection works in 1966—1968 showed that their postlabour effectiveness attained 85 to 95% in 10 days after dusting and fleas perished en masse during the first 1—3 days. However, deep dusting cannot be considered a prophylaxis measure of long duration in the control of fleas since on treated areas their number again became high in 2—12 months.

In chickens having had coccidiosis the absorption of Fe⁵⁹ in the thin part of the intestine noticeably increases. A considerable rise in the concentration of Fe⁵⁹ was observed in the thin part of the intestine, spleen and especially in the bone marrow. A hightened need of chickens for Fe is resulting from anemia intensively developing on a background of coccidiosis. In blind appendages (the place of the development of E. tenella endogenic stages) the specific activity of Fe⁵⁹ decreases that can be explained by intensive destructive processes in this part of the intestine.

Chickens were one or three times infected with oocysts of Eimeria tenella (100.000 oocysts per one chicken) in order to study the activity of phosphotases of the mucous coat of the thin intestine. It was established that a single infection of 20-, 40- and 60-day-old chickens decreased the activity of alkalinous phosphotase. The activity of acid phosphotase did not change. In the experiment with three successive infections these indices were different on the 20th day after the first infection and after each of two subsequent infections. On the 20-th day after the first infection no changes were noted while after two subsequent infections an increase of the activity of alkalinous and acid phosphotases was registered.

Laboratory tests were undertaken to ascertain the factors affecting the activation of dried and non-dried sporangia of Coelomomyces milkoi noted for high pathenogenicity to Tabanus autumnalis and Chrysops relictus. The activation of dried and non-dried sporangia poured with water and the emergence of zoospores from them carried out at a temperature of 10 to 40°. A temperature of 25 to 30° created optimal conditions for zoospore emergence. Zoospores emerged from dried sporangia poured with water after one to three year maintenance under laboratory conditions.

6866 larvae of Chironomus sp. were collected in boggy tundra of the Chaunskaya Inlet coast (north-western Chukotka). In 5 larvae (0.073%) cysticercoids of the family Dilepididae were found. The experimental infection of Calidris alpina nestlings has proved the belonging of these cysticercoids to Trichocephaloides megalocephala. The description of the cysticercoids and a cestode form developed from them is given.

In the southern spurs of Kuznetzky Alatau there was found a nidus of great abundance of the tick Ixodes pavlovskyi Pom. The area examined refers to aspen- fir- birch forest with well developed underwood. Here I. pavlovskyi prevails in number over I. persulcatus Sch. Of 51 series of I. pavlovskyi hungry imagos were isolated 12 strains of the tick-borne encephalitis virus that makes 23% of virus carriage in series and 2.6% — in specimens.

In a temporary water body, on an open area of the forest there were found larvae of Aedes annulipes infected with microsporidiosis. A microsporidia formed from 3 to 8 spores from one sporont. The variations in a spore size increased 3 µ.