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On the basis of analysis of the present-day distribution of feather mites of the family Avenzoariidae on taxonomic groups of birds and the comparison of the phylogenetic system of this family with those of corresponding taxa of their hosts a hypothetic picture of the evolution of the family in question on birds has been suggested. The three subfamilies of the family Avenzoariidae manifest to this or that degree a phenomenom of phylogenetic parallelism as well as a great variety of violations of this phenomenon. Members of the subfamilies Bonnetellinae and Avenzoariinae, associated with the most ancient orders of birds, demonstrate the most distinct picture of phylogenetic parallelism both with primary and secondary hosts and rare cases of their passage on to new groups of hosts. In the subfamily Pteronyssinae, connected with phylogenetically younger orders of birds, Piciformes and Passeriformes, distinct traces of phylogenetic parallelism are observed only in some phylogenetic branches of mites; the general picture of the distribution of this subfamily on hosts displays numerous cases of the transition of mites from one taxonomic groups of hosts on the others. The present-day distribution of mites of the family Avenzoariidae on taxonomic groups of host-birds is due to a complex of evolutionary processes: coevolution of mites with their hosts that manifests itself in the form of phylogenetic parallelism; independent adaptive evolution of mites; dying out of mites on individual phylogenetic lines of hosts; passage of the representatives of certain taxa of mites from one taxonomic group of hosts to another by way of ecological contamination.

Methods of quantitative estimation of critical photoperiod and critical date of entering the diapause in ixodids have been worked out. S-shaped dependence of the number of diapausing larvae and nymphs of Ixodes persulcatus on their feeding periods has been shown. It has been established that in Central Udmurtia the average critical date of entering the diapause in 50% of satiated larvae and nymphs falls at the 18th and 29th of June, respectively, with the light day length of 17 hr 10 min and 16 hr 22 min.

The fauna of fleas in the East Kisil-Kum includes 24 species. Different physico-geographic regions of sands are characterized by different spectra and number of species of fleas. The greatest share in collections is composed by Xenopsylla gerbilli caspica — the parasite of Rhombomys opimus. In autumn the other parasite of this rodent, Coptopsylla lamellifer, is a mass species. All the most significant and long changes in the number of these species are associated with changes in the density of their hosts' population. The most significant in epizootic respect is the flea X. gerbilli caspica from which about 50% of plague agent cultures were isolated.

Microsporidia Vairimorpha antheraeae is known to be a parasite of the cabbage looper Barathra brassicae. A number of passages through a non-specific host, the bee moth Galleria mellonella, resulted in changing the pathogenicity and breeding intensity of V. antheraeae. Isolates possessing high biological activity against G. mellonella are shown to be active against their primary host B. brassicae.

Analysis of literary data on Microphallus pirum (Lebour, 1907) Deblock, 1980, encysted metacercariae of which develop within daughter sporocysts, was conducted. It has been shown that descriptions of a free cercaria of this species are based on misunderstanding. Young metacercariae of species with M. pirum type life histories and cercariae embryos of M. pygmaeus have been described as "blastocercariae". To avoid the confusion it has been suggested to decline the term "blastocercaria" which was introduced by Deblock and Ky (1966). The transition from cercaria to metacercaria is marked by casting the tail away. Larval embryos of dixenic trematodes have the rudiment of this organ at early developmental stages which are regarded as morphogenesis of cercariae. In contrast to free cercaria of trixenic microphallids it is proposed to call them "cryptocercariae". The casting of the tail rudiment away by cryptocercariae marks the beginning of morphogenesis in metacercariae. It is shown that fundamental changes in morphogenesis are due to the exclusion of free cercaria stage from the life history of microphallid trematodes. The basis of these changes is the acceleration of development of organ systems which are necessary for a normal functioning of maritae and the retardation of larva cenogenesis formation. In microphallids with M. pirum type life histories the differentiation of genital primordium begins is the course of cryptocercaria development. In cercariae of trixenic trematodes the primordium is represented by a cluster of nondifferentiated cells. Besides, cryptocercariae lack stylet, glands and muscular tail which are necessary for a normal functioning of a free larva. In the course of M. pygmaeus morphogenesis cystogenous glands (last cenogenesis of M. pirum and similar species) are not formed.

Some general aspects and mechanisms of the formation of parasite fauna of fishes depending on the type and succession of lake ecosystems have been exposed by way of example of Karelian-Kola limnological region. The characteristic of the main types of lakes with allowance for parasitological data is given. The scheme of typology and evolution of lakes is suggested.

A comparative study of hydrolysis and transport of carbohydrates by the cestode C. laticeps and in the intestine of its host, bream, has revealed a considerable influence of the host's enzymes on the characteristics of the parasite's enzyme system. The cestodes have been found to possess effective transport systems of glucose absorbing it in an active way while in the intestine of bream during the glucose absorption prevail the mechanisms of simple and easy diffusion.

The paper deals with interrelations between the occurrence and specificity in different types of the host-parasite system. The higher the taxonomic level of hosts, to which the parasite's specificity is displayed (one link is formed), and the wider its occurrence at the lower levels, the more stable the unbalanced state of the host-parasite system in space and time.

Two new species of Myxosporea are described from fishes in Falkland-Patagonian area. They are Bipteria nototheniae from urinary canaliculus of kidneys of Patagonotothen ramsayi and Davisia galeiformes from urinary bladder of Lycodapus australis.

Female, male, larva and pupa of Simulium kachvorjanae sp. n. belonging to the group morsitans are described. The species is recorded in the forest-steppe zone of the Ukraine. Differential diagnosis of the species at different developmental stages is given.

A new nematode of the genus Metabronema recoroded in Coryphaenoides acrolepis and C. pectoralis of the north-western Pacific (the region of the Kuril Islands) is described. The new species is characterized by having a ring on the distal end of the male's small spicule, the absence of filaments on the eggs and by the position of the vulva near the female's anal opening.

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