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

The influent species are Heligmosomoides polygyru

s, Aprostatan drya macrocephala and Trichocephalu

s muris. Similarly to the dominant species, also the influent ones are often parasitizing M. arvalis and they are found in geobiocenoses where also the dominant species are present. Their infection index, however, is lower than that of the dominant species. Some of them are dependent on the occurrence of intermediate hosts (e.g. Apro statandrya macrocephala

). Under specific conditions and at a certain developmental stage of the M. arvalis population, the influent species may appear as dominant ones. The accessory species were the most numerous in our material. We can assign to them all remaining species recovered from M. arvalis (Tables 1-2). Their incidence of infection, infection index and mostly also intensity of infection are very low. The scale of accessory species is very large but very variable in the structure of the helminth fauna of M. arvalis. The accessory helminth species found in M. arvalis parasitized originally other species of hosts. This statement is supported by the following examples: The species Peligmosomoide

s skrjabini occurs only in localities where the populations of M. arvalis and the rodents of the genus Apodemus are mixed. The same concerns the species Skrjabinotaenia lobata

. The specimens of No- tocotylus noyeri were recovered from M. arvalis only in the areas where Arvicola terrestris was also present. Similar relationships were observed also with other accessory species. Discussion The results concerning the helminth fauna of M. arvalis have not been achieved by the same method. It is therefore very difficult and sometimes even impossible to compare and evaluate the data available at the present time. Nevertheless, we could use some records on helminth fauna of M. arvalis from the European part of the Palaearctic Region (Table 3)-