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In species of the genus Dermacentor the gnathosoma shape variation consists of two components: correlated (allometric) and uncorrelated with sizes of individual variation. Proportion of size-independed variation is different in the species studied. These species constitute the following morphocline. In D. silvarum proportion of size-dependent variation is the highest, while sex differences are the least expressed. In D. marginatus, the proportion of allometric variation is less and sex dimorphism is more expressed. In D. reticulatus, the sex dimorphism is also well expressed; besides it displays noticeable degree of size-independent variation of palpa shape within each sex. The data presented herewith seem to support any idea of D. (s. str.) reticulatus being more ancient phylogenetically as compared with species of the subgenus Serdjukovia.

In nymphs of Ixodes ricinus both induction or prevention, and also maintenance or cessation of morphogenetic diapause are controlled by two-step photoperiodic reaction of shortday-longday type. Unfed and engorged nymphs of Leningrad population of this tick are characterized by similar critical photoperiods of the shortday elementary reaction at 18° (18 hours of light p. d.) and at 25° (16 hours of light p. d.), but photoperiodic response of unfed nymphs is more distinct. The longday elementary reaction in engorged nymphs is also thermolabile, but dependence on temperature is characteristic here not for critical photoperiod (18 houre of light p. d. at 18 and 25°), but for an efficiency of longday influences.

Taxonomical analysis of minuta group in the genus Neotrombicula has been carried out. Descriptions of 6 species has been corrected. The main corrections are as follows. 1). In N. scrupulosa fD = 2H-(6-11)-(6-9)-(6-8)-4-... The common fD = 2H-8-6-6-4-6-2. 2). N. lubrica differs from N. minuta first of all by the number of setae in the 4th dorsal row and in the first rows of V, and also by more dense punctation of scutum. 3). N. irata has fD = 2H-6-6-6-2-6-2 but not 2H-6-6-6-4-4-4 as in description. 4). Both N. irata and N. lubrica has SB anterior to PL, and in N. lubrica it is more anterior than in N. irata. One new species, N. dimidiata sp. n. has been described from Western Kopetdagh and Northern Tadjikistan. The new species is similar to N. minuta and differs from it by the presence of 2 setae in the 4th dorsal row against 4 in N. minuta, lesser number of setae in the anterior rows of V, greater values of D and V mean lengths and by greater Ip. The species clearly differs from N. lubrica by the shape of the scutum and by more sparse punctation of it. For N. scrupulosa an analysis of geographical variability has been carried out. The methods used had been previously devised for ticks (Filippova e. a., 1995). Monotonic multidimensional scaling on 8 characters (AW, SB, PSB, SD, AP, AM, Dm and NDV) has been used to obtain the picture of relative distances between groups. Almost all measurable characters, fD and NDV in the species shows a significant variability, but intervals of their values for different populations are overlapped. Comparing the diagram showing relative distances between groups from different localities (fig. 4) and the picture of their disposition on the map (fig. 5), one can conclude that it is a case of a cline, stretching approximately in the latitudinal direction. For N. corvi, N. lucida, N. scrupulosa and N. lubrica new hosts and/or new localities are pointed out. The distribution of N. minuta is probably restricted in the Southern Ukraine. Steppes and similar biotopes in Caucasus, Bashkiria, Northern, Eastern and Southern Kazakhstan, Altai Territory, Tuva and Mongolia are inhabited by another species, N. scrupulosa. In the mountains of the Middle Asia minuta-group is represented by several species appeared to be local.

The egg-laying activity in the fleas Leptopsylla segnis Schonherr declined when their number on the host (white mouse) was risen from 2-5 to 20. However, if the number of the parasites on host exceeded 30 the egg output per female increased. It is supposed, there is an density-dependent regulation of egg-laying activity in L. segnis, which operates in certain diapason of flea abundance. It appears that mechanism of this regulation is supressed by heavy infestation.

It is underlined, that the genital ducts in dilepidids may pass either dorsally or between the osmoregulatory ducts within a genus, species (Alcataenia) or even a strobilae (Birovilepis spasskayae). So, the opinion of Mathevossian (1963) is confirmed by the new material, that this feature is a characteristic of taxa of specific (if it is so), but not generic rank. The same case is observed in the pattern of alteration of rostellar hooks as well as their relative length in rows - a variety of combinations may exist in the same genus (Alcataenia, Vitta, Choanotaenia). The ratio of the main dimentions of scolex organs (rostellar apex diameter: suckers diameter, length of rostellum: suckers diameter, rostellar apex diameter: length of rostellum) is proposed for generic diagnosis. The new genus Glareovitta gen. n. is erected. The type and recently single species Glareovitta alexandri (Korniushin, 1966) comb. n. parasitizes the Black-winged Pratincole Glareola nordmanni (Charadriiformes: Glareolidae). The genus is characterized by the absence of egg filaments. Thin uterine capsules mentioned by Korniushin (1966) are thought to be outer egg envelopes, as in Icterotaenia, Monopylidium, Sobolevitaenia. The new genus differs from the genera mentioned above by unarmed suckers, proportions of scolex organs, relatively small cirrus pouch, and shape of the ovary. The feeding habits of its host, the pratincole, is rather peculiar: unlike other typical plovers these birds take a food in a flight, alike swallows.

Qualitative heterogeneity and its quantitative expression in geographically distant populations of Proteocephalus percae were studied. A wide spectrum of the possible values of the characters within which the expression of features is determined by environmental conditions, was detected.

The life cycle of Proteomonas brevicula in the experimentally invasied bugs of the family of Nabidae was studied. It was shown, that the development of parasites takes place in the rectum of the hosts. The only endogenic agglomeration of parasites was observed during the first 7 days. Then the group of the flagellates, which localised on the surface of the rectal glands, forms the transmission stages - endomastigotes. Two types of the cellular cycles, which realised in the life cycle Proteomonas brevicula correspond to the cellular cycles of the two strains of the flagellates representing the laboratory cultures of the Proteomonas. The fine structure of the P. brevicula as well as the modes of attachment of the parasites to the cuticular intima of the rectum were examined with the transmission and scanning electron microscopes.

570 males of Golden Hamsters were divided into 3 groups: I - free from invasion, II - once infected, III - repeatedly infected. Diurnal activity of cyclic nucleotides and enzyme of pentose-phosphate cycle (G-6-PhDG) was investigated in spring, autumn, and winter at 3, 7,11 a. m. and 3, 7,11 p. m. The Golden Hamsters once infected with opisthorchiasis do not show any seasonal changes in G-6-PhDG activity, but this invasion influences the total content of protein, diurnal oscillation of which depends upon seasons. In spring time the repeated invasion induces the diurnal rhythms of G-6-PhDG and of total protein content. Diurnal stereotype of cyclic nucleotides (cGMP, cAMP) demonstrates the dependence upon seasons and invasion frequency without any changes of the average diurnal level.

The morphology and ultrastructure of two new species of the aseptate gregarines Mastigorhynchus bradae sp. n. and Kamptocephalus mobilis sp. n. are described. The problem of the using of some ultrastructural features in taxonomical diagnoses is considered. The question of the including of both new-described species to the family Lecudinidae is discussed. Genus Kamptocephalus. Lecudinidae. Mucron is simple, not separated from the body, with apical smooth area, made up by the junction of epicytar folds' tops and thus the system of the radial tunnels is formed; hooks, exfoliations and papillae are absent. A structure of epicyte is aberrant: basal layer is absent, tops of the folds are flattened, and there are micropores on their lateral surfaces. Apical arcs are present; typical apical filaments are absent, however similar structures lie at the lower part of the basal layer. Type species - Kamptocephalus mobilis. Kamptocephalus mobilis sp. n. Trophozoites are elongate, ca. 110 X 30 µm. Mucron is rounded. Epicytar folds are elongate on the cross-section. There are 7-9 apical arcs and 9-11 apical filament-like structures. Nucleus is sphaerical, 13-21 µm, contains 1 excentric rounded karyosome. The other stages unknown. In Flabelligera affinis, middle gut (White Sea). Genus Mastigorhynchus. Lecudinidae. Similar to septate forms. An anterior part is transformed into the attachment organelle and is separated from the body by the circular string. It consists of a conical basal part and a whipe-like apical one. This apparatus could be thrown off. A structure of epicyte is aberrant: the folds have flattened tops and lack apical and filaments; micropores are on lateral surfaces of the folds. Type species - Mastigorhynchus bradae. Mastigorhynchus bradae sp. n. Trophozoites are elongate, cylindroid. <> is ca. 150 µm in length and ca. 35 µm in width; basal part of the attachment organelle is ca. 42 µm in length. Epicytar folds are trapeziform on the cross-section. Nucleus is spherical, ca. 14-29 µm, lies in the centre of <>. The only lens-like karyosome lies across the longitudinal axis of the body adjacent to the rear wall of the nucleus. The other stages unknown. In middle gut of Brada villosa (White Sea).

The complex influence of nitrate potassium and temperature on the movement activity and duration of glimmerial epithelium of gills of Anodonta cygnea in a norm and under the invasion with sporocystes Bycephalus polymorphus have been investigated. The increase of concentration of the nitrate potassium solution (from 10 to 1000 mg/l) decreases progressively the movement activity and its duration in ciliae, specifically in heavy invased individuals. The increase of temperature by each 10° (from 8 to 28°) together with the toxin concentration 28 mg/l decreases 2-3 times the duration of cilia activity, that corresponds the value of Vant-Hoff coefficient (Q10), while under the concentration 280 and 2800 mg/l it influences талу times more.

New species of the trematode Hemipera magnaprostatica from the hake Merluccius merluccius senegalensis cautched in the West Sakhara's waters is described. The trematodes of this genus are found in the Central-East Atlantic fishes for the first time.

A new earlier unobserved phenomenon was stated for the host-parasite system: increasing of the abundance of the specific S. lucioperca gills parasite - A. paradoxus after its decreasing instead of a continued decrease of the host abundance. It is proposed that such phenomenon is a marker of the critical situation of the host population.

A review of parasitological contributions made by A.V. Ivanov - the member of Russian Academy of Sciences, an eminent zoologist, morphologist and evolutionist is presented. He is an author of many papers on morphological descriptions of different taxa of parasitic gastropoden molluscs, their structure and morphogenesis, taxonomy and ancestry. Several his papers deal with Udonellidad - the Turbellaria parasites of marine Crustaceans. There are also several review on adaptations to parasitic style of life. This is why he has taken a honorary place in the parasitology. Many of his publications are to be considered as classic models of scientific studies.

Summary is absent.