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The inhibitory analysis has shown that E. tenella does not include ready folic acid into metabolic process but synthesizes its metabolite, 7.8-dihydrofolic acid (DHFA), from its precursor, para-aminobenzoic acid (PABA), which enters the host's organism. PABA can be fully substituted in the process of metabolism by sulphadimesin (SD) at the molar ratio PABA : SD = 1 : 16.7. As a concurrent antagonist of PABA SD is 6 times stronger in the parasite-host system of Coccidia than in bacteria in cultural medium. The increase in PABA content in relation to SD more than 1 : 16.7 intensifies the viability of Coccidia that is expressed in higher lethality of chicks, which reaches its maximum at PABA : SD = 1 : 1.25. A further increase in the content of PABA does not affect the host's lethality. The decrease in PABA in relation to SD lower than 1 : 16.7 reduces the viability of Coccidia. Nucleic bases G, A transforming in the organism into corresponding nucleotids and aminoacids, I-metionin and glycine, which are the products of biosynthesis with a participation of DHFA, do not stimulate the viability of E. tenella that apparently is associated with the non-capability of the host to assimilate timidin.

The influence of Lamblia on the hydrolysis of fat by lipase was studied in vitro. The hydrolysis rate of fat in the presence of live Lamblia and without them was determined colorimetrically by the quantity of the formed glycerine. In addition, the kinetics of this reaction was studied by the method of compensating potentiometry by neutralization of fat acids with alkali. The intact organisms were found to cause an inhibition of fermentative hydrolysis of fat. The importance of this fact from the point of view of interaction in the host-parasite system is discussed.

The data concerning biological peculiarities of spores of Myxosoma cerebralis obtained by the author and other researchers are summarized. The life cycle of M. cerebralis is well adapted to the seasonal cycle of the host owing to the fact that the infectivity of the spores is attained only after 4 months of aging in water and that the spores are highly resistive to freezing and drying. No sexual process during 4 month aging was observed. It is supposed that the maturity of spores depends to a great extent on the ability of polar capsules for extrusion.

Three types of cells (reserve, digestive and secretory) differing in their ultrastructural characters were found to exist in the epithelium of the midgut of nymphs of O. papillipes during the blood assimilation. Reserve and secretory cells are dominant at the first stage of digestion while digestive cells are most abundant at the second one. Ultrafine structure of secretory and digestive cells points to the labile relationship between these types of cells. The same digestive cells assimilate blood both by means of phagocytosis of formed elements and by pinocytosis of its liquid components. The identity of ultrastructural peculiarities of endocytosis and intracellular blood digestion in ixodid and argasid ticks is shown.

Experiments conducted during all seasons have established that F. hetera, one of the mass species of fleas in Mountain Altai, can be infected both by the strain of selective virulence typical to this nidus and by the non-typical non-virulent mountain-altai strain of plague agent. The non-virulent strain does not form in fleas the block of proventriculus and within 1.5—2 months they become free from the microbe. At the infection with the typical strain of the altai subspecies rare transmissions of the agent to Pallas' pika can take place as well as its long preservation in fleas.

The method of statystical analysis of the distribution of the 2nd and 3d instar larvae of Hypoderma bovis in 54 herds (8120 heads) of cattle from Czechoslovakia and in 20 herds (1809 heads) from Mongolia has shown that in most cases the negative binomial distribution models the distribution of larvae with sufficient reliability and that the variability in parameters of the distribution is stable independent on the parts of the area.

A comparative-karyologycal study of 12 species of black flies of the genus Prosimulium was carried out. Species referring to the groups hirtipes and macropyga have similar karyotypical characteristics differing in general in the degree of ploidy of chromosomal sets. Species which form the group alpestre possess peculiar karyologycal characters occupying due to this an intermediate position between the genera Prosimulium and Helodon. They should be separated into a distinct superspecies taxon, Ahaimophaga Chubareva et Rubzov gen. n. P. multicaulis differs karyotypically from other species of the genus Prosimulium but displays a great resemblance to species of Helodon; due to this it should be assigned to the latter.

The description of female, male genitalia and the fourth instar larva of a new species of mosquito, A. (О.) sergievi, from the Tuva ASSR (South Siberia) is given as well as data on its breeding places. It belongs to spring and early summer species and breeds both in fresh and salt waters. Anal gills in the larvae breeding in fresh waters are significantly (P > 0,001) longer than those from salt waters (mean ratio between the upper anal gill length and saddle length is 2/3 and 1/2, respectively). A. sergievi is apparently related to East Asia steppe zone (Mongolian — Chinese formations): besides Tuva, it is found in East Kazakhstan and may occur in Zabaikalye, Mongolia and North China.

The activity of imago, habitats of preimaginal stages, intensity of the autumn hatching of imago and the initial period of their hibernation were investigated in summer-autumn of 1975 in the Kalmyk ASSR. The activity of winged insects in September was rather high, decreased in mid-October and ceased virtually by the beginning of November. The pupation and emergence of midges take place up to the second decade of October. IIId and IVth -instar larvae hibernate.

A new species of monogeneans, Dactylogyrus tauricus sp. т., is described. The species was found on the gills of Alburnoides bipunctatus fasciatus from the Alma river (Crimea, USSR).

The spontaneous development of cysticercoids in the strobile of cestodes of Oochoristica sp. is described. The cysticercoids were found in the body cavity of Eremias velox Pal. Such development is supposed to be due to an anomalous localisation of the parasites.

Psilotrema simillimum has one intermediate host, the mollusk Bithynia leachi. Cercariae emerging from the mollusk encyst in the environment. Adolescariae become infectious in 3—7 days. In the definitive host trematodes become mature on the 9th day. The development of miracidium in an egg finishes in 19 days at 20—24C. Egg, miracidium, redia, cercariae, adolescariae and marites obtained in the experiment are described.

Two larval species of the genus Metorchis, M. bilis and M. xanthosomus, are reported from fishes of West Siberia. Larvae of the first species can develop into adult forms in birds (terns, gulls, ducks) and in mammals (cats, golden hamsters, white mice). Larvae of the second species developed only in ducks. Experimental infection of golden hamsters, white mice and black terns with M. xanthosomus failed. On the results of the experimental infection and literary data the synonyms, M. bilis and M. xanthosomus, are given.

A study was conducted on the changes in sulphhydryl groups in the haemolymph of Lymnaea stagnalis infected with partenites of Opisthioglyphe ranae, Planorbis corneus infected with partenites of Cotylurus cornutus and females of Viviparus viviparus infected with partenites and larvae of Echinoparyphium petrowi. At the infection in the haemolymph of hosts were recorded statystically reliable changes in the protein sulphhydryl groups which are blocked by toxines excreted by the parasites. The reduction rate in the content of these substances depends on the localization of the parasites and infection intensity of the hosts.

In the housings for live-stock flies of S. stercoraria eat up engorged mosquitoes and play a significant role in the regulation of their number.

After examination of sandfly collection from Agdam (Azerbaijan SSR) it was stated that all sandflies previously identified as Phlebotomus mongolensis belong to another species Ph. jacusieli. Ph. jacusieli has not been recorded in the fauna of USSR before. Probably all records of Ph. mongolensis in Transcaucasia are wrong. Description of Ph. jacusieli and some ecological data are given.

14 species of fleas were recorded from 173 nests of 47 species of birds. Most abundant of them are Ceratophyllus vagabundus, C. gallinae, С. borealis. The abundance of fleas was found to depend on season and hosts' habitat. The above species were most frequently encountered in nests in May. The high abundance index of fleas was registered in birds nesting in hollows, burrows of small mammals and in clefts of rocks.

For the first time data are given on the infection of larvae of gad flies with two species of Gordius sp. The infection intensity of larvae collected near water bodies at the low reaches of the Desna river was from 20 to 66.7%. The data obtained on the intra-cavity developmental period of Nematomorpha as well as on the infection intensity are of great interest due to unsufficient information on this phenomenon.

Summary is absent.

Summary is absent.

Summary is absent.