Dr. Kassai Tibor - Dr. Murai Éva szerk.: Parasitologia Hungarica 6. (Budapest, 1973)

of pseudogeohelminths belongs the nematode Trichocephalus muris and to ageohelminths Syphacia sp

. A special position have the larval stages of cestodes (

Hydatigera taeniaeformis

, Taenia tenuicollis

, Taenia crassiceps

) and the larval stage of the nematode Porrocaecum sp

. for which M. arvalis serves as the intermediate host. 3. Topical structure This structure is characterized by the prevalence of species parasitizing in the small intestine (9 species); in the caecum parasitize 4 species. Two helminth species were found in the liver, 1 species in the large intestine, on the stomach wall in cysts, on the intestinal wall in cysts and free in the body cavity (Tables 1 and 2). 4. Quantitative structure When evaluating the quantitative structure not only incidence and intensity of helminth infection but also the index of infestation should be considered (KISIELEWSKA, 1970a - infection index). It can be applied not only for the numerical expression of the dynamics of a certain species of parasite in a certain period, but also for the determination of dominant, influent and accessory species of parasites, also with respect to ecological conditions. The examinations of our material show that, according to the infection index, the dominant parasites of M. arvalis in Czechoslovakia (Table l) are the members of the genus Syphacia and Heligmosomum

. These parasites have not only a high incidence and index of infection but also a high mean intensity of infection. They are best adapted to their host and accompany the populations of M. arvalis in the geobiocenoses which are most suitable for their life.*1 x

^ PELIKÁN (1959) records that Microtus arvalis is a typical inhabitant of grass-lands and frea areas. The specimens of Microtus arvalis, which he captured in Czechoslovakia

,originated from the following types of terrain: 40% field, 25% meadows and similar grass-grown areas, 20% fallows and bare boundaries. Only 3% were found in shrubs, A-% in wet grounds and 2% in forest.