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Isozyme analysis of mMDH in Crithidia asclepii and C. oncopelti by means of electrophoresis and densimetry method suggests the diploidness and genetic exchange in these organisms. Synthesis of mMDH in C. asclepii is checked by duplicated polymorphic loci MDH-1 and MDH-2, each with two alleles. In C. oncopelti two "daughter" loci are functioning too, polymorphic MDH-1 with 3 alleles and monomorphic MDG-2. Resemblance and differences in the isozyme spectra of mMDH can be used for taxonomic purposes.

Protein spectra of two parasite-host systems were studied by means of gel chromatography and disk electrophoresis: ectothermic (Eubothrium crassum — Salvelinus lepechini) and endothermic (Diphyllobothrium dendriticum — Larus fuscus). The level of low molecular proteins and proteins with high electrophoretic mobility in tissue extracts from D. dendriticum and liver of L. fuscus was higher than in extracts from E. crassum and liver of S. lepechini. These differences are, apparently, due to a great difference in temperature of hosts' internal media (fish — 10 to 15C, bird — 40C).

Characteristics and differential diagnosis of the new genus Oschmarinetta are given. The type species is O. leipoae (Johnston et Clark, 1948) comb. n., syn.: Raillietina (R.) leipoae J. et C., 1948 from brush-turkeys of South Australia. Many genera of davaineid cestodes with unpaired genital system, their morphological characters are enumerated. Some notes on the systematics of davaineids are made in connection with the revision of the collective genus Raillietina.

The nervous system of Dicrocoelium lanceatum and Fasciola hepatica is formed as orthogon including endon and a system of paired longitudinally oriented nerve trunks which are united by transverse commissures. The specific characters of the nervous system of D. lanceatum and F. hepatica are as follows: the location of the peripharyngeal ganglion, topographical anatomy of paired pharyngeal nerve, the character of structure and ways of direction of the paired cephalic nerve, localization and function of additional ganglia.

The evolution of the head of the Cucullanina has some parallel processes. At first, there is a reduction of the head receptors (from 18 in the family Quimperiidae to 4 in some members of the family Cucullanidae). Secondly, the concentration of the receptors around the mouth takes place. And at last, all head receptors in these nematodes have a tendency to be morphologically identical. The background of these processes is the reduction of the six initial lips and the development of the different fixatory devices. Most primitive apparently are the nematodes which heads have numerous morphologically different receptors (these receptors have dispersive arrangement). The most progressive nematodes are probably those that have a reduced number of the receptors on the head. Such receptors have a reduced concentration and morphology. The processes mentioned above are accomplished parallel in different systematic groups of the Cucullanina. Thus, the ways of getting equal structure and arrangement of the nematode head sensor organs in different taxa may proceed independently.

The main distal receptor complex of mites belonging to 21 species of the genus Haemogamasus was studied by means of scanning electron and light microscopy. The tarsal complex contains a similar number of sensillae of 5 types and includes 4 porous thin-walled and 3 porous thick-walled setae (probably olfactory receptors), 12—14 grooved setae with cavities and fine canals in thick walls (probably thermoreceptors), 4 smooth setae (taste organs), and 2—3 microsetae of unindicated function. All sensillae are arranged in two groups thus forming 2 functionally different parts of the complex. Relative position of each hair within the complex is identical in all the species studied while the differences between the species concern mainly the setae size.

Field experiments were conducted during the settling of young animals of Citellus pygmaeus in four areas 4 to 13.6 hectares in size. From 3 to 6 animals were caught in each area and labled by administering radioactive substance (0.5µ of glycine 14C or methionine 35S) and colouring hair on the head. In a day or two labled sousliks were caught again and in 6—7 days a total catching of animals and collection of ectoparasites from their hair and burrows done. In all, 942 sousliks were caught in the experimental areas and 2624 specimens of fleas of different species and 2305 ticks of R. schulzei collected. The average number of fleas which were labled on one little souslik for a day was 0.1 to 2.3. The number of labled fleas in the above areas coincided with the number of fleas infected with plague in the areas of epizootia. The level of parasitic contact in settlements of little souslik cannot provide the development of plague epizootia by transmission of the agent through fleas.

Comparative karyological studies of the subspecies T. autumnalis autumnalis and T. autumnalis brunnescens were carried out. Karyotypes of these forms differ distinctly in the structure of Y-chromosome.

Studies of the effect of P. gallinaceum on Ae. aegypti in different periods of the agent's sporogony and during different gonotrophic cycles of the vector have shown the absence of strong inhibition of mosquitoes' fecundity.

The biology of Aedes impiger Walk, from the polar region of the European part of the USSR has been studied and literary data have been summarized. Its biological peculiarities such as rapid and simultaneous development of larvae and pupae, a short period of seasonal activity, long daily activity, the presence of autogeny and long obligate diapause provide a distinct localization of the active period of the life cycle within a season. A. impiger develops quicker than other spring species of mosquitoes, emerges the first and can serve as phenoindicator for specification of developmental periods and mass emergence of bloodsucking mosquitoes.

A study of the electrolytic contents of blood serum, erythrocytes and muscles of carp infected with Ichthyophthirius multifiliis was carried out. Whatever the infection intensity, a characteristic increase in the cations K+ and Na+ ratioin the plasm and muscles of infected fishes takes place. The above dependence, which is expressed in the intensification of active ions transport, is associated with mobilization of organism's protective functions.

A new microsporidian parasite of a freshwater crustacean Cyclocypris ovum L. from the lake Vrevo in the Leningrad district is described by means of light and electron microscopy methods. Infected specimens were found in autumn in less than 1% of the population. Microsporidian parasites seem to develop in the connective tissue and fat cells. Numerous sporoblasts are formed by means of rosette-like budding of multinuclear sporont's plasmodium. The sporont's membrane is retained and it plays a pansporoblastic envelope role. The spores are oval-elongated, in freshwater smears measuring 3.4 (3.3—3.5) x 1.7 (1.6—1.8) µ. Exospore is two-layered, endospore is well developed. The anchoring disc has a typical form, the polaroblast is lamellary, occupying 1/4—1/3 of the spore's volume. The polar filament is anisofilar and appears as 2—3 coils of the thick part, one intermediate coil and 4—6 coils of the thin part in a single layer. The spore is uninuclear. Preliminarily, the new microsporidian species is regarded as belonging to the genus Vavraia.

Having examined a collection of myxosporidians the authors describe 3 new species: Leptotheca quadritaenia from the gall bladder of Epigonas telescopus, the only representative of the species which has 2 long ribbon-shaped appendages on the tops of the valves, Leptotheca simplex from the urinary bladder of Hippoglossus hippoglossus, Trilospora minuta from the gall bladder of Coryphaenoides rupestris. The latter relates to the Trilosporidae Schulman, 1959, family from which the only one species T. californica Noble, 1939, was known.

Description of a new species Dactylogyrus narzikulovi from gills of Varicorhinus capoeta cheratensis natio steindachneri from the basin of the Amudarja River (Central Asia) is given.

The paper reports the initial stages of the formation of ecological parasitology in the Leningrad University in thirties. A special attention is paid to the activities of A.A. Philipchenko (1884—1940) whose role has been little known up to now.

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