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A laboratory culture of Ornithodoros papillipes free of spirochaetes was infected with Borrelia sogdiana by feeding on guinea pigs having spirochaetemv of blood. During the next 9 years spirochaetes were passed exclusively transovarially in 8 subsequent daughter generations of ticks. According to the data on the infection rate of ticks with spirochaetes the frequency of the transmission of the pathogen by infected females increased from 11 per cent in the parental generation to 47 per cent in the VII^th daughter generation, and the infection rate of the female progeny in the generation in question from 10.7 to 29.8 per cent. In 3 of 14 investigated lines of the VIII^th daughter generation the spirochaetes lost their virulence for guinea pigs. It is suggested that in the case of normal circulation of spirochaetes between mammals and ticks the strains of the pathogen are constantly affected by the disruptive selection and genetically polymorphic. In the case of the passage of spirochaetes only via ticks the disruptive selection is replaced by the direct one that increases the ability for transovarial transmission. Substrains of the pathogen become more monomorphic and in a number of cases lose their ability to develop in mammals.

It is suggested that the intimate contact between the first instar larva and tissues of the host is the most important reaction in the immunological relationship in this disease. Various larval tissues are antigenic, but haemolymph from the third instar larva is most convenient for use in serological studies. Shock reactions are probably due either to the reaction of antibodies in the tissues of a previously sensitised host with larval secretions and excretions, or to the direct reaction of mid-gut material from dead larvae with the host tissues, whether these contain antibody or not. The toxic activity of the midgut material of the first instar larva has probably been underestimated. Several new lines of approach to the problem of the host-parasite relationship in hypodermosis are suggested, including possible work on the likely lipidophilic metabolism of the first instar larva of Hypoderma bovis.

During the "rodent—flea—rodent" circulation of the causative agent of plague some periodical changes occur in the agent's phenotype. These changes are associated with various conditions of existence of bacteria in the organisms of two different hosts: vertebrate animal and flea. The above scheme of the development of the bacterial population suggests the life cycle of the agent of plague — obligate parasite.

The article concerns two ways of realization of the morphological ability of integument in some gamasids for extension of the cuticle reduction of hard plates and extension of the epicuticular folds. The attempt was made to correlate these two ways of extension of the soft cuticle with two types of parasitism in Gamasoidea. It is shown that nest-burrow bloodsuckers such as Dermanyssus gallinae are characterized by the extension of the epicuticular folds whereas the reduction of hard plates is common to "pasture" mites (Ornithonyssus bacoti, Sauronyssus saurarum, Ophionyssus natricis).

A new species Aedes (Ochleratatus) montchadskyi from the basin of the Ili river belongs to the communis group. The adults differ from Ae. pullatus by variegated femora, mesotergit without longitudinal dark bands and the absence of lateral abdominal triangles of light scales. The hypopygium differs from that of Ae. detritus by a wider wing of the claspettes and a wider basal lobe which is twice as wide as high. Larvae differ from Ae. leucomelas and Ae. caspius by 2—3-branched frontal hairs, a more slender siphon (index 3.3—3.5) and long barbed 3-branched lateral hair of the saddle.

In the Crimea and Turkmenia, where Phlebotomus papatasi occurs in abundance, sandflies were caught by means of light traps with aspirator and 250 W electric lamp. In the Crimea Ph. papatasi did not get into the light traps. In Turkmenia Ph. papatasi was attracted by light as well as the other species of sandflies. The above differences are apparently due to ecological peculiarities of this species in different geographical zones.

Dactylogyrus aristichthys was introduced in the USSR in the fifties during the acclimatization of Aristichthys nobilis in ponds. Recently an increase in the number of these parasites has been recorded that resulted from a high density of introduced fishes. All age groups are susceptible to the infestation. The parasite is located on inner lateral sides of gill leaflets. D. aristichthys develops at warm time of the year, at water temperature from 14° to 30°. Eggs develop outside the host. The duration of embryonal development depends on temperature: at 30° larvae hatch in 2 and at 5—8° in 16 days. Larvae live in water for 8—11 hours; they are localized for the first time in mouth cavity and later on leaflets. The life cycle of D .aristichthys (from egg to adult) makes 11 to 13 days at water temperature from 17 to 23°. Maximum infestation rate is several thousands of parasites per a fish and falls on July. Due to such high infestation rate these parasites are very dangerous.

In the basin of the Amu-Darya the species of parasites normally characteristic of the Balkhash province of the Mountain-Asiatic subregion and those occurring only in the Turkestan province are recorded as being dominant. In the basin of the Syr-Darya palaearctic and mediterranean species are known to be dominant, the mountain-asiatic species being small in number. Differences in the parasite faunas of fishes from the Amu-Darya and Syr-Darya may serve as a basis for distinguishing Amu-Darya and Syr-Darya districts within the Turkestan province of the Mediterranean subregion.

During studies of the medium on which ascarids (Ascaris suum) were maintained the following cultures were isolated: Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris and Enterococcus sp. All isolated cultures were sensitive to colimicin and micerin. To inhibit the microflora in the medium and in the intestinal tract of ascarids it is expedient to use colimicin together with micerin and nistatin. Such combination provides for 100 per cent sterility of the medium and 90 per cent sterility of the intestine of the cultivated ascarids.

Concurrent registration of locomotor activity of ventral and dorsal neuromuscular bands in ascarids, which were not separated from their anterior part, has shown certain regularities. The separation of their anterior part has changed the character of their rythmic activity. Locomotor activity of the ventral band represents intermittent contractions alternating with relaxation, whereas the dorsal band produces continuous contractions and relaxations of the same frequency and amplitude. With the separation of the anterior part or under the effect of nanophin or diplacin (1.10^-4 g/ml) there are observed changes in the locomotor activity of dorsal and ventral bands. These changes are probably due to different innervation of bands. This suggests that the rythm of dorsal bands is miogenous and that of ventral ones is neurogenous.

Three species of the genus Nadejdolepis were found among 29 species of hymenolepidids collected from charadriiform birds during the Chukotka helminthological expedition of the Academy of Sciences of the USSR to the Anadyr lowland in summer of 1961. A new species Nadejdolepis ansa sp. n., was found in the greater sand plover (Charadrius mongolus Pall.). The paper contains a description of these species.

95 muskrats from the Tomsk region were examined. In the gill bladder of 15 animals (15.8%) the fluke Opistorchis felineus (Rivolta, 1884) Blanchard, 1895 was found. The intestines of 11.1 and 17.7% of animals contained the remains of pike, roach and crusian carp. Defficiency in vegetable food and regular winter mass deaths of fishes in water bodies inhabited by muskrats leads to the feeding of the latter on dead fishes and consequently to infestation with O. felineus. A constant connection of muskrats with aquatic: media favours a regular infestation of water bodies with eggs of the parasites and maintains a high degree of fishes infestation with metacercarians that increases the danger of infestation of man with О. felineus.

Nyctotherus cordiformis from Rana temporaria bears bipolar and shortened somatic kineties, a thigmotactic dorsal stripe, noted for a first time and a series of cilia-free sutures (preoral, dorsal, subapical, caudal and caudo-lateral). The preoral ciliary apparatus (PCA) includes prefundibular and infundibular parts with 60 and 40—45 membranelles, respectively; no secondary PCA was found. Villeneuve-Brachon's hypothesis (1940) of the origin of Nyctotherus from Metopus via M. circumlabens was carefully reexamined and confirmed, excluding an intermediate species; it may be a fresh-water species of M. es-type. The kinetome and PCA's changes were traced step by step in the line Cyclogramma — Dexiotricha — Tetrahymena — Protocruzia — Blepharisma — Metopus — Nyctotherus; ecological aspects of this evolution are discussed. Nyctotherus is not unique within the order in possessing polytenic chromosomes in exconjugant stages; polytenization was observed in Metopus, Brachonella and might be expected to occur in at least 12 genera with 210 species of Heterotrichida. In its turn, Nyctotherus gives rise, independently, to Plagiotoma and to a short Clevelandella — Paraclevelandia line. Paranyctotherus seems to be a trichostome (family Balantidiidae).

Some information is given on the multiplication of toxoplasms of RH strain. During 5—6 days after infection intensive multiplication of toxoplasms takes place in the cells of mesothelium, in macrophages, histiocytes and omentum. "Pseudocysts" are formed as a result of multiplication of one or more trophozoites having penetrated into the cell. The multiplication stages of toxoplasms resemble most of all the longitudinal fission. However trophozoites lying in pairs may be formed due to copulation of isogametes. The presence of dumb-bell-shaped nuclei in many trophozoites and dividing nuclei in paired individuals speaks, however, in favour of longitudinal fission. The possibility of hologamic copulation is confirmed only indirectly. In addition to small trophozoites large ones, which may be taken for zygotes, are occurred sometimes. The technique of fluorescent cytophotometry of nuclei stained with auramin 00—SO₂ has revealed three groups of trophozoites with nuclei containing different quantity of DNA: the 1^st group with inconsiderable amount of DNA (4—8 conv. units); the 2^nd group with double amount of DNA (10—16 conv. units). Indices of DNA in both groups may correspond either to pre- and postsynthetic amount of DNA or to its haploid and diploid content. The first supposition is more probable. The 3^d group is very small and characterized by inconsiderable amount of DNA (16—38 conv. units). These are either dividing nuclei of zygotes in the postsynthetic phase, which is less probable, or nuclei of trophozoites ready to the consequent binary fission characteristic of schizogony. Thus in the postsynthetic phase, the nucleus will have a four-fold amount of DNA. Then, 4-nuclear schizonts are formed which divide into four trophozoites. Large polynuclear schizonts have not been detected. Stages of en-todiogenia were not detected by the Romanovky-Gimsa method. Together with longitudinal fission there are binuclear individuals in which nuclei are located along the longitudinal axis of the body. No sexual processes seen to occur in toxoplasms.

Summary is absent.

Summary is absent.