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

to compare our results with those of other authors. Although the material was compiled with regard to the incidence of infection only (Table 3), it is quite obvious that the accessory species prevail in the helminth fauna of M. arvalis. Most numerous among the dominant species are the members of the genera Syphacia, Heligmosomum

. The literary data confirm our previous statement that the accessory species parasitize M. arvalis only under specific ecological conditions and in the case of other vertebrates, especially of rodents and hares, they occur only in the area where M. arvalis is distributed. For instance ERHARDOVÁ (1957, 1958) and MITUCH (1966-1970) recovered Tri che st rongy1

as re

tor

taef

orm

is from M.arvalis only in habitats where also Lepus europaeus was found to be infested with this nematode species. Similarly Tri churls opaca and Q

uinqueserial

is quinqueseri

alis were found by ERHARD OVA (1958) only in the area where Ondatra zibethica was distributed. ERHARDOVÁ (1958) and MITUCH (1966-1970) identified the species Notocotylus noy

eri in the distribution area of Arvicola terrestris. ROSICKY (1959) recorded that Hymenolepis fraterna and Hymenolepi

s diminuta parasitized M. arvalis only in areas where also other small rodents, especially Rattus norvégiens, occurred. An important feature of the former cestode is its dominance in Mus musculus. The same is certainly true also of other cases: the trematode Brachylaemus recurvus (found by PROKOPIC, 1971) and the nematode Longistriata schul

zi (found by MITUCH, 1966-1970) were recovered from M. arvalis only in the area where the rodents of the family Gliridae occurred, and the nematode Strongyloides ratti (found by SCHMIDT, 1961) in the area where Rattus norvegicus was distributed. With some other species parasitizing M. arvalis, which according to the present knowledge seem to belong to accessory ones, it is very difficult to state which are their original hosts. It concerns, e.g., the species MoniliforIt concerns above all the individuals or populations of Microtus arvalis living under conditions which make possible their life but are not very suitable and typical for Microtus arvalis under conditions of the European part of the Palaearctic region, e.g. wet grounds, forests, human dwellings, or fallows, bare boundaries", shrubs - see KRATOCHVIL (1959).