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It was established that for the distribution area of the species of helminths of migrating animals should be taken only that part of the earth surface on which its natural populations can develop for a long time completing there their biological cycles. Those areas where helminths occur as «brought in» can be called zones of dispersion. The helminth species always has its own distribution area the borders of which do not usually coincide with those of the hosts. When studying this relationship it should be taken into account that the helminth species is a parasite of not only one species of hosts but of the whole systematic or ecological group. The broadening or narrowing of its distribution area Within a historically short period of time is possible only as a result of man's activity.

A description and figures of four monogenean species of the genus Horricauda are given: H. bychowskyi sp. n., H. nagibinae sp. n. and H. trilobata sp. n. from the gills of Rhynchobatus djiddensis and H. forficata sp. n. from the gills of Rhinobatos hynnicephalus (South-Chinese and Yellow Seas).

At the infection of Pulmonata (Lymnaea stagnalis, L. peregra, Planorbarius corneus, Planorbis planorbis) and Prosobranchia (Viviparus viviparus) with partenites of trematodes the changes in haematological indices were noted, which depend on the participation of haemocytes in the protective reactions of the organism. As part of the study of haemolymph of freshwater molluscs statistically reliable differences in the size of cellular elements, besides eozinophilous microgranulocytes, and statistically reliable reduction in the nuclear-cytoplasmatic relation in infected P. corneus were established. The infection of molluscs with partenites of trematodes is accompanied by the increase of the total amount of haemocytes and by their diminution in size.

Data on the life cycle of the trematode Hasstilesia ovis are given for the second time in order to point to the errors occurring in helminthological literature. The species has one intermediate host, the terrestrial molluscs Pupilla muscorum and Vallonia costata. Cercariae are turned into metacercariae without leaving molluscs. Pathomorphological changes in the intestine of the sheep caused by these parasites are described. The authors came to the conclusion that the parasites have a pathogenic effect upon the host and cause a disease which should be called hasstileosis.

The species Metastrongylus confusus Jansen, 1964 parasitic in bronchia of pigs and wild boars was first recorded from the territory of the USSR. Its wide distribution (Byelorussia, the Caucasus, Transcaucasus territory, Uzbekistan) is noted. The description of the species and its figures are given.

A description of two species of Allantonematidae, parasites of the flea Ceratophyllus tesquorum Wagner, Psyllotylenchus tesquorae sp. n. and P. curvans sp. n. from Ceratophyllus turbidus Roths and the mermitid Pulicimermis ceratophyllae gen. et sp. n. from Ceratophyllus caspius Iof et Argyropulo is given.

The diameters of toxoplasms' cysts in native preparations of brain of bredless and inbred mice (AKR and CC57BR) infected with the toxoplasms of Czech low-virulent strain were measured. It is shown that the growth of cysts ceases by the 7th week from the infection and the ratio between cysts of different sizes does not change for 38 weeks and more. The curve of the ratio between cysts of different sizes, which in the period of infectious process stabilization is close to the even distribution curve, is apparently a result of primary parasitemia. By the 1st year of the infection a reactivation of the infection in some animals occurs judging by the rise of the number of small cysts. Stabilization and then reactivation of the infection are correlated with the dynamics of humoral antibodies.

Tests on the feeding of larvae of Ixodes persulcatus and I. ricinus on five species of Muridae have shown that forest and common voles have congenital protective reactions limiting the number of successfully fed parasites. Such congenital resistance is practically absent in common field mice and does not arise during the following parasitism of ixodid larvae. The congenital resistance is absent from steppe lemmings too but protective reactions limiting the number of successfully fed larvae arise during the further parasitism: of ticks.

A key to nymphs of five species of Dermacentor from central Asia is given. To recognize differential characters laboratory nymphs from the parents identified previously by the authors were reared. D. montanus and D. pavlovskyi are studied from one, D. reticulatus and D. niveus from two and D. marginatus from four geographical areas. The shape of scutal scapulae, structure of the anal valve, proportion and topography of peritremes, shape, size and number of scutal setae, shape of alloscutal and pleiral setae, proportions of auricles, hypostome, cheliceral bases and different parameters of palpal joints, structure and size of coxae I—IV and tarsi I, sizes of scutum and different parameters of gnathosoma are taken for specific diagnostic characters. The differential characters were checked on laborator nymphs of D. reticulatus, D. niveus and D. marginatus and on those collected beyond the territory of Central Asia.

The results of every day collections of adult Ixodes persulcatus in experimental fixed areas are compared with the data of a single collection of these ticks in the analogous areas. In the period of seasonal maximum of ticks the single collection amounts to 20% of the total number of activating individuals. The nature of activation and sex ratio in activating ticks are considered.

A new diagnosis of the genus Metanalges is given. Four species of this genus from different birds (the family Rallidae) were found: M. rallorum, M. grossus, M. fortis and M. crexi, sp. n. A key to males of this species is given. A new species, M. crexi sp. n., is described from corncrake Сrex crex captured in Kursha Spit, the south-eastern coast of the Baltic Sea. The new species is close to M. curtus but males differ from those of the latter by the shape of the opistosomal cleft, shape of lobes and interlobal membranes. M. crexi has no external membranes between setae l₅ and d₅.

The analysis of results of many year regular collections of ixodid ticks has shown that females (56%) were dominant in I. persulcatus while in I. ricinus were dominant males (52%). The ratio between sexes in both species changed noticeably as in individual years so during the imago activity season. In summer collections of I. lividus females were dominant every year, the share of which accounted on the average for 70% and varied from 69 to 75% within different seasons and from 60 to 83% within imago activity season. During hibernation and in spring the share of males and females was nearly adequate.

A more accurate description of the myxosporidian Sphaerospora pectinacia found in the perch, Perca fluviatilis, from Luvozero Lake (Karelia) is given. The vegetative stage as a disporous plasmodium is described.

Some problems of the biology of Myxobolus pavlovskii, a parasite of Hypophthalmichthys molitrix and Aristichthys nobilis cultivated in the ponds of the Krasnodar Territory, are studied. The dynamics of the parasite development on the host and the maturation speed of spores of myxosporidians depending on water temperature are shown.

Summary is absent.

Sporocysts and cercariae of E. pancreaticum from Bradybaena lantzi and metacercariae of this species from Conocephalus fuscus collected in Kazakhstan were studied for glycogen contents. It was established that glycogen occurs mainly in the form of granules β. It is found in tegument, in sub tegumental muscular layer, in parenchyma and suckers.

Summary is absent.

Summary is absent.

Summary is absent.