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Sanitation of the mollusk population with highly effective cercaricide preparations can be used for the control of opisthorchosous infection. Low concentrations of molluskocides which are sublethal for non-infected mollusks have turned to be lethal for hyperinfected individuals. All tested molluskocides display a cercaricide effect in concentrations which are considerably lower than molluskocide ones. Low concentrations of cercaricides are toxic both for cercariae and parthenites from the liver of mollusks and for freely swimming cercariae. Disastrously affecting the freely swimming cercariae microdoses of cercaricides prevent the infection of the second intermediate hosts. Microdoses of cercaricides which are lethal for cercariae are not toxic for the majority of hydrobionts including fishes of all age groups. As far as the dynamics of the infection level of Bithynia with O. felineus is characterized by a one-peak curve with a distinct peak in the middle-end of July the treatment of water bodies with microdoses of cercaricides should be carried out just in this period.

Data on the biology and morphology of cercariae of Diplostomum phoxini (Faust, 1918) Arvy et Buttner, 1954 are given. The cercariae were found in Radix auricularia from the middle part of the Burulcha river (Ukranian SSR, Crimea). In November, 1974 the invasion extensity of mollusks was 16.3%. No cercariae were found in spring and summer samples.

Three new species of cystophorous cercariae, Cercaria appendiculata Pelseneer, 1906, C. octocauda Tschubrik, 1952 and C. saccocaudata Tschubrik, 1966, are described from the gastropod Tectonatica clausa (Broderip et Sowerby). C. saccocaudata is a larva of trematodes of the genus Lecithaster. The development of parthenites of this species carries out within one summer season. Parthenites of C. appendiculata and C. octocauda are capable to survive unfavourable winter conditions and produce cercariae in the next summer. The above three species were found to eject cercariae through the ejaculatory tube which is an important adaptation of chemiurids to the infection of the second intermediate hosts.

The data are given on the morphology of cestodes of the genera Gyrocoelia Fuhrm., 1899 and Infula Burt, 1939. It has been found that in the spermatheca of the female of G. perversa there are spermatozoids with an elongated head typical for Plathelminthes. In the spermatheca of the female of I. burhini were found spermatids with long tails. The final formation of spermatozoids in I. burhini takes place in the spermatheca. The taxonomic position of the species of Gyrocoelia found in the waters of the USSR has been made more precise: G. polytestis Saakowa, 1952 and Gyrocoelia sp. II Schaldibin, 1960—1961 are reduced to synonyms of Infula burhini and Gyrocoelia sp. I Schaldibin, 1960—1961 to a synonym of G. perversa. The number and size of the hooks of proboscis in the species of the genus Gyrocoelia vary in wide ranges and cannot be used as a taxonomic character. The number of testes and the structure of the egg membrane are constant for the species of this genus.

Studies were carried out of the permeability of the cuticle of Trichinella spiralis (Owen, 1835) for fluorochromes and histidine, the filling of the mid-gut and the aminoacids contents in it. The quantity of glicogene in different organs was estimated. A conclusion has been grown that a larva consumes food through the integuments of its body; intestinal Trichinella use within the first 20 hours of their development the reserves of glicogene and later consume food monomeres and oxygen from the host's mucous membrane through their integuments. The mode of feeding of Trichinella was formed during their evolution as an adaptation to parasitism on the mucous membrane of the host.

Data are given on the effect of warm waters of the Kanakovskaya hydro-electric power station on the infection level of the roach young with myxosporidians. 1641 one-year old specimens of roach were examined. 11 species of myxosporidians are reported from the zone of warm waters influence while in the control gulf beyond the warming zone — only 7 species. Within the larval period only two species, Chloromyxum legeri and Zschokkella costata, were recorded. Their developmental cycle was retraced. Under the influence of warm waters the developmental period from plasmodium to spore in Ch. legeri is accelerated: from 20 days in "cold" waters to 15 days in "warm" ones. In winter period in warm water zone a sporeformation of many species of myxosporidians takes place. At the same time the infection with plasmodial stages keeps on a high level that indicates to a continuous active feeding of the young even in winter.

A new method was employed for studies of parasite-host relationships between ixodid ticks and their hosts. It has been established that ixodid ticks are able to desensibilize the reactive sensibility of the host and to satiate themselves without unhibiting the latter. Every day and long parasitism of the ticks on cattle (in nature) and increasing doses of secretion of the ticks' saliva (sensibilizer) lead apparently to the weakening of the host's organism (desensitization). However, under laboratory conditions in hosts a resistence to bites of ixodid ticks can appear.

Adult individuals of I. persulcatus are characterized by uneven assimilation of nutrients in digestive cells of the mid-gut. In the mid-gut of females and males exist simultaneously parts with different degrees of exhaustion. Physiological age of a hungry individual is determined by three items: "main" physiological age; degrees of exhaustion "accompanying" it; and, in addition, by different degrees of exhaustion of individual digestive cells in the limits of one portion of the mid-gut. Calculation of the area of the portions of the "main" and "accompanying" degrees of exhaustion has shown that the former is always maximum one. This suggests the availability of different food resources in hungry ticks of different physiological ages.

10 strains of Francisella tularensis were isolated from 4 species of gamasid mites, Laelaps muris, L. multispinosus, Hyperlaelaps amphibius and Haemolaelaps glasgowi, in natural nidi of tularemia in the Tumen district. Under experimental conditions L. muris is often infected with tularemia agent on sick animals but preserves it at an indoor temperature not more than a week and does not transmit it transovarially. Haemogamasus ambulans preserve the agent within the same period. L. muris and Hirstionyssus isabellinus do not transmit the tularemia agent to healthy animals through a bite.

The paper presents data on the specific composition, number, hatching sites, seasonal and daily activity of mosquitoes attacking man and reindeer and the influence of weather factors on the attacking activity of mosquitoes in Central Siberia. 23 species of 3 genera are reported from Central Siberia as follows: Anopheles maculipennis, Culiseta alaskaensis, Aedes beklemishevi, A. cantans, A. caspius dorsalis, A. cataphylla, A. communis, A. cyprius, A. diantaeus, A. excrucians, A. fitchii, A. flavescens, A. hexodontus, A. impiger, A. intrudens, A. leucomelas, A. nigripes, A. pionips, A. pullatus, A. punctor, A. rempeli, A. sticticus, A. cinereus.

Under experimental conditions fleas X. cheopis engorged and assimilated blood of 4 species of rodents, man, pigeon and two species of reptiles. Histological investigations have shown that the structure of food clot, destruction rate of blood cells and general duration of digestion are change ed considerably depending on the host's blood. In females the digestion of white mice blood to haematin at 23—24° lasted not over 12 hours, the digestion of blood of hamsters and man — 12 to 20 hours, of guinea pigs and reptiles — 18 to 25 hours and of white rats and pigeons — from 20 to 30 hours. In males the digestion carries out somewhat slower. The above differences in blood digestion can apparently create unequal conditions for pathogenic microbes in the intestine of fleas that affects the preservation and reproduction of the agent in the organisms of these carriers.

A very rare case of development of warble fly on non-specific host Microtus in Hissar mountain in Tadzhikistan has been established.

On studying the changes in the epithelium of the mid-gut of Ceratophyllus tesquorum, C. laeviceps and Leptopsylla segnis intranuclear crystals were found during the process of digestion. They were recorded both from young and adult insects. The crystals were absent from nuclei of cells of regeneration nests, epithelium of the fore-intestine, any other organs or from nuclei of epithelial cells of the stomach of young non-feeding individuals. They were found neither in young nor in adult individuals of Xenopsylla conformis and Neopsylla setosa.

The effect of 0.2—2 mg/g of insectine (Bacillus insectus) upon the Ist-IInd stage larvae of X. cheopis is very negligible but it manifests itself in the subsequent low (9 to 30%) development and hatching of imagos. The III stage larvae are more resistent and after the effect of 10 mg/g of the preparation 9% of larvae formed cocoons which later developed into imagos. Adult fleas poorly responded to 0.2—2 mg/g of insectine. However, 10—30 mg/g of insectine caused in four days a mass death of fleas and their population decreased to 70% as compared to control.

A comparative study was carried out of the synthesis of DNA, RNA and protein in blind appendages of the intestine of healthy and infected with E. tenella chickens. It was established that the inclusion of P³² into DNA and C¹⁴-orotic acid into RNA increases in 2—10 days after the infection. An intensive inclusion of C¹⁴-lysine into protein of blind appendages was observed in 2—6 days after the infection of chickens. Under the effect of the parasite an activation of metabolism of DNA, RNA and protein takes place in blind appendages of the host's intestine.

Two new species of myxosporidians with gigantic spores are described from the gall bladder of Alepocephalus australis caught at 1500 m depth. Both species differ in gigantic sizes of spores that apparently is characteristic of myxosporidians of fishes inhabiting such great depths.

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