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The theory of natural focality by Academician E.N. Pavlovsky, illustrated with examples of the fundamental types of corresponding diseases was expounded at the general meeting of the USSR Academy of Sciences on May 29, 1939. In the 30 years which have elapsed since then the theory has been widely acclaimed, and its basic principles applied in epidemiologic research by different institutes in many parts of the Soviet Union and many foreign countries. The theory of diseases with natural foci has been included in parasitological and epidemiologic textbooks and manuals.

The degree of identity of antigenic properties of haemolymph from 3d instar larvae and saline extract from newly hatched 1st instar larvae of Oedemagena tarandi was determined by Boyden—Stavitsky method of passive hemagglutination. The blood serum of guinea pigs, which were injected with haemolymph from 3d instar larvae, was employed as antiserum. With 8.2 ppm protein concentration the solution of haemolymph fully inhibited the ability of the antiserum, specific to this antigen, to agglutinate the erythrocytes treated with haemolymph of 3d instar larvae. The extract from 1st instar larvae didn't inhibit hemagglutination even with 1050 ppm protein concentration. In evaluating the results obtained and in carrying further investigation on immunity to warble-flies larvae it should be taken into account that antigenic properties of material from 1st and subsequent instar larvae are likely not identical.

The fauna of gamasid mites from lemmings of Vrangel Island comprises 11 species and lacks endemics. In microbiocoenoses of lemmings' nests dominating species of mites are as follows: Hirstionyssus isabellinus, Haemogamasus ambulans and H. nidi. In nests of the Arctic lemming (Dicrostonyx torquatus Pallas) Laelaps semitectus is very small in number, in nests of the Siberian lemming (Lemmus sibiricus Kerr.) the number of L. lemmi is insufficient. Most abundant species on animals are Hirstionyssus isabellinus (on D. torquatus) and Lael. lemmi (on L. sibiricus). In years of mass reproduction of lemmings the density of mites in biotopes varies from 1—2 to 10—13 thousand mites per 1 hectare.

Seasonal changes in the population of the mite Allodermanyssys sanguineus Hirst from Kirghizia were studied both under laboratory and natural conditions, in nidi of the distribution of this species. Eggs laid in various seasons are unequal physiologically. Protonymphs of the autumn population have a longer duration of life than have those of the spring-summer population. Mites can hibernate in protonymphal, deutonymphal and adult (females) phases. Protonymph is the main hibernating phase. Most abundant are mites in August and September. On the basis of seasonal changes in the number of mites and laboratory observations A. sanguineus can be referred to relatively xerophilous species among gamasid mites.

Three species of small rodents, which are very abundant in the forest zone of mountain Crimea, are hosts of larvae and nymphs of ixodid ticks. The adults of these ticks parasitize mainly ungulates. Differences were noted in the infestation of mice (Apodemus flavicollis Melch. and A. sylvaticus L.) and vole (Microtus arvalis Pall.) with ixodids. Among different age groups of rodents the highest infestation was observed in adult males.

The paper deals with the structure of the genus Pygmephorus Kramer, 1877 in a comparative aspect of two systems: Krczal—Sasa (Krczal, 1959; Sasa, 1961) and Gross (Cross, 1965). As a result of analysis of material and literature the author accepts the viewpoint of Krczal—Sasa: Pygmephorus is regarded as a distinct genus with the subgenera — Krczaldania, Вakerdania, Brennandania and Pygmephorus s. str.

The paper contains descriptions of 5 new species and substantiation of 4 new genera of monogeneans of the subfamily Ancyrocephalinae: Hemirhamphiculus armatus gen. et sp. n., H. similis sp. n., Parahemirhamphiculus pinguis gen. et sp. n., Atherinicus cornutus gen. et sp. n. and Diversohamulus tricuspidatus gen. et sp. n. They differ from other known genera in a number of characters concerning both the internal structure of the worms and some details of the structure of their adhesive mechanism.

The paper presents data on the development of Dactylogyrus extensus from egg to adult at a temperature of 14—15°. At this temperature the whole cycle lasts 18 to 20 days. A comparison of the author's data with materials of Prost (1963) and Paperna (1964) has shown that the opinion of D. extensus as a psychrophilic form is erroneous. D. extensus is a thermolabile species which can live and reproduce both at low and high temperatures.

Acetylcholinesterase and butyrilcholinesterase topographically associated with the nervous system were found in trematodes by means of Gerebtzoff's method (1959). Apparently, cholinenergetic transmission of nervous impulses is characteristic for trematodes. The division of the body into locomotor and genital portions in most of trematode species affects the structure of their nervous system. In the anterior (locomotor) portion longitudinal nerves are thickened and connected with ring commissures, in the posterior (genital) portion they are poorly developed and ring commissures are absent. In some species (Diplodiscus subclavatus, etc.) there is no division of the body at all due to some peculiarities of their biology. In this case the nervous system is uniformly developed along the whole body.

The paper contains a detailed description of metacercaria of the genus Diplostomum (D. petromyzi-fluviatilis), a specific mass parasite of the brook lamprey. Its first description published by Diesing in 1850 was insufficient.

8 species of cestodes of the genus Echinocotyle are found by the author in 348 specimens of waders of the Black Sea coast (Kherson district). Of them 7 species were for the first time recorded from the Ukraine. The description, figures and differential diagnosis of a new species, Echinocotyle ukrainensis sp. n., are given. The new species differs from other related species in smaller hooks (0.024—0.026 mm) of the proboscis and structure of the copulative apparatus. The distinct species status of E. uralensis (Clerc, 1902) is confirmed. The paper presents some information on hosts, time of detection of each species of cestodes and new redescriptions of most of them.

A new species of nematodes — Encephalonema ophthaltina Tchernobay, sp. n. (Filariata) — was found in the eyes of two species of Corvidae. Microfilariae reach remarkably great size. Females are described, males are unknown.

A new species of the genus Ergasilus (E. tissensis) was found on gills of some Cyprinids in the basin of the Tissa river (1962—1964). The paper contains a description of Ergasilus tissensis Djachenko sp. n. This species is close to E. sieboldi Nordmann.

The crossing was carried out of stem eelworms from onion, strawberry, and red clover which developed in onion bulbs. Experiments were set up in bulbs of onion. Parental pairs in six combinations gave productive progeny. Reproduction of hybrids between stem eelworms from red clover and strawberry was weaker than in parental forms. The number of other hybrid populations and the number of eelworms in control tests was almost equal. Among hybrids there were solitary specimens with morphological anomalies, mainly in the form of the tail. In two cases serious breakage was noted in the development of genitalia. The subsequent generations are to be studied.

In cytoplasm of nerve' cells and in foci of decay of myelin membranes of the white substance of patients dead of the diffuse sclerosis there were found peculiar bodies defined by the author as microsporidians (Encephalitozoon cuniculi). Polymorphism of the bodies is considered to be various stages in the life cycle of this species. A definite association was established between the presence of parasites in the brain and chronic diffuse sclerosis.

Cryptobia cyprini Plehn, 1903 is a causative agent of cryptobiosis in carp, common carp, goldfish and tinch. The effect of its pathogenic properties was also observed upon Ctenopharyngodon idella Val. There was observed mass mortality of these fishes from cryptobiosis caused by intensive reproduction of flagellates in the blood of the fish. Local sick fishes, Cyprinus carpio and Carassius auratus gibelio, were found to be the source of infection.

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