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On the basis of morphological, zoogeographic and ecological data the evolution of fleas of the family Ischnopsyllidae has been analysed. Peculiarities of the host-parasite relationships in the family Ischnopsyllidae consist in their connection with relatively young families of Chiroptera: Vespertilionidae and Molossidae. Data on the connections with more ancient families Emballonuridae, Megader-matidae and others are lacking at present. The time of origin of the family Ischopsyllidae can be dated back either to Paleocene or, that is more likely, to the end of Eoceneabeginning of Oligocene. The place of origin of the family Ischonopsyllidae is south-eastern Asia. From here on the tribes Chiropteropsyllini and Ischnopsyllini spread over in Afrotropical, Indo-Malayn and Golarctic regions, the tribe Porribiini in Australian while the tribe Sternopsyllini in Neotropical region. Ancestors of the tribe Sternopsyllini reached South America via Australia and Antarctica. Fleas of the tribe Nycteridopsyllini penetrated into North America from Asia via their Beringian bridge later.

Investigation of the composition of Arthropod population in rooks' nests was carried out from 1981 through 1988 in forest-steppe and steppe of West Siberia (the Omsk District). In the ranges of the investigated territory the nidicolous population in the rooks' nests is practically uniform in its composition and abundance dynamics that depends on the nature of the colony position and biological peculiarities of rooks affecting the nest microclimate. Foretic relations between taiga ticks and rooks, without involving feeding on birds, are first noted.

The infection of mosquitoes with malaria plasmodia was found to be affected by relative (to full portion) blood amount of the infected donor, which they suck out, i. e. to what extent the engorged portion approximates to the limiting one when mosquitoes cease bloodsucking. The facts obtained show that the survival of plasmodia in a mosquito (most likely, the passing of ookinetes into the outer side of the mid-gut) is associated with the degree of its stretching during bloodsucking. The limit stretching may be also attained during feeding up on a healthy donor.

Closely related species of the genus Dermacentor Koch (the subgenus Serdjukovia Dias), D. marginatus Sulzer, 1776, D. niveus Neum., 1897, D. ushakovae Fil. et Pan., 1987, have vast distribution areas and display parapatric and partially sympatric relationships. Differentiation of these species by larva was worked out earlier mainly on the basis of morphometric characteristics of microscopic features with the use of elementary statistics methods (Filippova, Panova, 1985, 1988; Filippova e. a., 1986). In this case larvae from a laboratory culture of preliminary identified parents were used along with the ones from nature. Of 20 studied characters on the basis of Student's criterion for differentiation of D. ushakovae and D. niveus from D. marginatus were used: the scutum median seta length and its ratio to the width of cheliceral basal joint, length of the 2nd pair of preanal and epimeral setae; for differentiation of D. marginatus from D. ushakovae was used the length of the 1st pair of sternal setae and from D. niveus — the gnathosome width and the ratio between the gnathosome length and its width, as well as the ratio between the length of median setae of scutum and that of alloscutum setae. Methods of elementary statistics do not offer a common set of characters for a simultaneous identification of the three species. By means of discriminant analysis were studied noncorrelated characters of the same set and from the same samples (populations) of the above species: in all 11 samples, each consisting of 20 individuals. The ratio of median seta length to cheliceral basal joint width gives the highest number of coincidences in groups (species) (73.8 to 76.8%). There was developed a set of characters which intensify the effect of the above ratio: length of gnathosome, length of hypostome, length of cheliceral basal joint. The combination of these characters has made it possible to identify reliably the three species and has given the following coincidence in groups-species: D. ushakovae — 78.8%, D. marginatus — 80.0, D. niveus — 95.6%; on the average — 83.6%. Thus, only 16.4% of individuals were identified incorrectly. Then, by means of discriminant analysis of 11 groups-samples it has been shown what samples (populations) of each species deviate from coincidences in groups-species and to what extent they participate in the formation of the 16.4% of individuals, i. e. in what geographic points the overlapping of characters is most possible. Formulas for identification of the species in question by larva, obtained by means of the discriminant analysis, are suggested. The substitution of correspondent values of sizes into three formulas gives three values of X. An individual belongs to the species which has the maximum value of X.

Data are obtained on the fixation strength of carbohydrases on the structures of digestive-absorptive surfaces of cestodes and intestines of their fish hosts. A dependence of the parasite's digestive activity on the activity of the host's enzymes has been established. General regularities of desorption dynamics of carbohydrases in studied animals and their specific peculiarities are noted.

NAD dependent malate dehydrogenases of three trematode species, Notocotylus attenuatus, N. ephemera and N. imbricatus, have been investigated by electrophoresis. Seven different zones with 15 isoenzymes in N. attenuatus, 16 isoenzymes in N. ephemera and 11 isoenzymes in N. imbricatus have been found in MDH spectra. Isoenzymes of MDH are controlled by seven polymorphic locuses. The activity of isoenzymes of three slowly migrating zones is 10 and more times higher than that of fast zones (4—7). The genotypes of adults in one strain are genetically identical, independent ot the development in different definitive hosts. The spectra of MDH of the investigated Notocotylus species are different in slowly migrating isoenzymes (1—3 zones).

The development of microhemipopulation of parthenites of the trematode Philophthalmus rhionica, parasitic in Melanopsis praemorsa molluscs, is studied. The ways of migration of maternal and distribution of daughter rediae in the host are ascertained and the formation of germinal material of parthenites of different generations is examined in detail. Redioid embryos are suggested to develop from generative cells, distributed diffusely in the parenchyma of parthenites (free generative cells) and embryos of cercariae are formed from generative cells, which are components of germinal mass.

On the basis of examination of Clerc's preparation from a typical series (the Museum of Natural History, Geneva) and collections of the museums of the USSR and some foreign countries the validity of the species Aploparaksis pseudofilum (Clerc, 1902) has been restored and the list of its synonyms and definitive hosts in given. The life cycle of A. pseudofilum has been studied experimentally. Metacestodes belong to a modification of cysticercoid, a typical diplocyst, and are located in the coelom of intermediate hosts, oligochaetes: Bryodrilus arctica (Bell, 1962), Henlea diverticulata Cejka, 1912 (Enchaetraeidae); Octolasium lacteum (Oerly), Nicodrilus roseus (Sav.), N. caliginosus (Sav.), Eisenia foetida (Sav.), E. nordenskioldi (Eisen), Eiseniella tetraedra (Sav.), Dendrobaena octaedra (Sav.) (Lumbricidae).

Helminths are regarded as a lateral branch of the evolution progressively adapting to peculiarities of the ecological niche. The transition to endoparasitism is a consequence of allomorphosis due to which free-living forms of organisms could develop a new, qualitatively distinct, habitat. The ability to membrane digestion, which is thus acquired by integumentary tissues of helminths, leads to a reduction of the alimentary canal through substitution of the function. Emerging from relatively primitive ancestral forms endoparasites have achieved notable progress in the adaptation to a parasitic mode of life both in biological and morphofunctional respect and combine a high degree of species-specificity during their adaptation to definite hosts with sufficient plasticity of the adaptive reaction during hostal irradiation.

By means of immunochemical methods a considerable increase in Ca2+-transporting glycoprotein (GP) in liver tissues of golden hamsters at early stages of opisthorchiasis has been established. On the 3rd day after the infection GP amount increases 6 fold, on the 7th day — 15 fold. On the 14th day GP amount decreases but does not reach the control level. The control level is reached only on the 22nd day after the infection of animals. Ca2+-transporting GP belongs to the system of electrogenic transport of Ca2+ in mitochondria (MCh) and its increase in MCh of the liver is, apparently, the basis of destructive changes of these organelles.

In solutions of the detergent «Kristall» (0.9 and 90 mg. l.-1) there were established statistically reliable differences in the values of day rations and duration of food passing both in infected and free from infection molluscs. In non-infected individuals day rations increase 1.5 to 5 times and the duration of food passing 5 to 7 times. In infected animals the value of day rations decrease and the duration of food passing increases less intensively.

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During three weeks visit to U. K. the author has visited universities of Liverpool, Exeter, Birmingham and Stirling, as well as the Laboratory of Fish Diseases in Weimouth and the section of parasitic worms of the Natural History Museum in London. He had many talks with specialists in Fish Diseases and Fish parasitology, delivered several lectures.

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Summary is absent.

Summary is absent.