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Females and males of ixodid ticks (Ixodes and Dermacentor) infected parenterally with the tick-borne encephalitis virus at the adult or nymphal phase and containing the virus in the saliva are able to transmit the agent in the first minutes after the bite of the sensitive animal host. Preservation of the cement conus produced by saliva in the animal skin enhances the infection intensity because the quantity of the virus in the conus is comparable with that in the tick's body. The virus quantity in the fluid saliva, excreted by I. persulcatus females and measured during different periods of bloodsucking (at least during the first three days), increases 10 to 100 times in comparison with a comparable volume of hungry ones.

The formation of aggregations of related females is a peculiarity of the intrapopulational organization of long-tailed souslik that results in the accumulation of Citellophilus tesquorum, the main vector and keeper of the plague microbe in the Tuva plague nidus. The plague agent is adapted to the existence on the territory occupied by aggregations of females that manifests itself in the delay of the beginning and prolixity of block-formation periods in fleas. The transfer of the agent from one place to another takes place only at the high abundance of long-tailed souslik. When the number of the souslik is low the plague microbe circulates in the ranges of one or several neighbouring aggregations of females having no possibility for succesful transfer to a new place.

Results of studies of gamasid mites and argasid ticks collected from 12 species of bats from Pribaltica and Leningrad district are given. There,were found 1 argasid species (the most northern point on the territory of the USSR) and 16 species of gamasids (6 spinturnicids and 10 macronyssids), 15 of them are new for this region. Ornithonyssus pipistrelli is new for the USSR and Macronyssus crosbyi is new for Palearctic. The dominating species of gamasids are recognised.

Amino acid composition of water-soluble and water-insoluble proteins of 8 strains of Tr. vaginalis is studied. 17 amino acids are found in both protein hydrolyzates. Despite the complete coincidence of their qualitative compositions there are reliable differences in the quantitative contents of some amino acids. Differences in the contents of main amino acids of water-soluble proteins of different strains reflect the belonging of the latter to different sero-groups. No reliable differences in the quantitative contents of amino acids of both water-soluble and water-insoluble proteins in strains belonging to one sero-group are recognised.

In connection with the localization of G. dogieli in tissues of definitive hosts, in the parasites there are observed characteristic adaptive transformations, which lie in the emergence of powerful fixing mitotrichia, stimulation of the secretory function of the tegument, modification of the suckers and strong development of longitudinal muscular layers in the strobila. The complex proboscis system of the worms includes glands of syncytial structure which release secretion products into the environment. Cytoplasmatic processes of the walls of excretory canals are found to surround the elements of the nervous and genital systems, thus forming peculiar primitive envelopes around the latter.

The dependence of immunological reactions of fishes infected with Ichthyophthirius multifiliis infusoria was elucidated. The invasion of the parasite results in the activation of the immune system, increased phagocytosis and a growth of the activity of oxydase enzymes. With the increased number and sizes of parasites a decrease of the above parameters below the control values is observed. Changes of the immunological values are most dynamic at high (20—25°) and they are slower at low (10°) temperatures.

The ability of different helminths to secrete lysozyme during their development has been revealed. Postparasitic larvae of the helminths and mature individuals do not posess such an ability. The level of lysozyme contents in the host's haemolymph depending on the degree of parasite's maturity as well as its contents in non-infected insects was studied. The role of helminth's lysozyme as a factor of the rise of non-specific resistence of the host-parasite system is discussed.

The effect of host infection doze (10, 100, 1000 eggs) and developmental stages of helminths (larvae, adult nematodes) on the relationships in the system "Toxascaris leonina — Alopex lagopus" was studied experimentally. It has been established that 100 eggs are the threshold dose for helminths and 1000 eggs for the host. More distinct changes in the indices are characteristic of the parasite. Dynamics of host-parasite relationships in the development of the parasitic process correspond1 to helminth developmental stage. Larvae of T. leonina are most pathogenic for the host.

A progenetic form of Caythocephalus (truncatus?) cestode was found in Gammarus hirsutus from waters of West Tien-Shan (Talassky Alatau). Its description and figure are given. A possible reason of progenesis origin in C. (truncatus?) is considered.

The effect of water temperature on sexual maturation of D. vastator was studied. It was established that sexual maturation period is in reverse relation to water temperature. With temperature increase from 10 to 28° the time necessary for reaching sexual maturity decreases from 18—20 to 3 days beginning from the moment of parasites attachment to gills of carp young. The period from the emergence of the first sexually mature parasites to maturation of all individuals decreases from 3 to 1 day. The question of sexual maturation periods of parasites of this species in different parts of their distribution area is discussed.

In «Lotos» detergent solutions of 10, 50 and 90 mg/l-1 there were established statistically reliable differences in the contents of haemoglobin, density and active reaction of haemolymph of molluscs infected and non-infected with parthenites of trematodes. In the control group of infected and non-infected individuals statistically reliable are the differences in the density of haemolymph while in experimental group differences are statistically reliable in all indices.

The ultrastructural transformation of the extrasporal coat of the microsporidia Holobispora thermocyclopis and Lanatospora bosminae was revealed. Under the influence of water the cavity between the extrasporal coat and the spore wall is formed and seems like the sporophorous vesicle. The biological role of this transformation of extrasporal coat is discussed.

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