Abstract：An infection of primary polycystic echinococcus was found in the liver of a gerbil,Meriones unguiculatus Milnc Edwards during a survey on the infection of alveolar echinococcus in rodents which was undertaken in 1999 at the Hulunbeier Pasture of northeastern Inner Mongolia,China Of 45 gerbil,one (2 22%) was found infected with primary polycystic echinococcus consisted of many exogenous vesicles on the whole surface of this metacestode The larval cestode situated superficially in a liver lobe of the gerbil,it was not completely surrounded by host liver tissue,it is therefore not difficult to be dissected out total without rupturing it The dissected primary polycystic echinococcus was a short conical body measuring about 7 5mm in length,3mm in width and 2 5mm in thickness Only its base portion with fibrous tissue was attached to gerbil liver tissue and closely surrounded by connective tissue of host The sections of the metacestode showed that all the exogenous vesicles have arisen directly from germinal tissue of the parasite,it happened prior to onset of exogenous proliferation The sizes of exogenous vesicles were 0 141～0 724×0 432～0 752 mm in cross section specimen The base portion of the metacestode consists of fibrous tissue,the exogenous vesicles were also found attaching to the lateral edges of the base portion From the sections of the base portion,many strong PAS positive mass were observed These germinal tissue masses were structurally similar to that observed in the alveolar metacestodes of Echinococcus sibiricensis Rausch and Schiller,1954 and Alveolaris hulunbeierensis Tang et al ,2001 (Tang et al ,2001;2002;etc ) Histochemistry study showed that the germinal tissue between exogenous vesicles and in the internal surface of exogenous vesicles walls had reticular appearances,and were filled with large number of PAS positive granules bodies measuring about 2 3μm in diameters Other spherical or conical buds of early stage endogenous vesicles with different sizes (6～16×6～8μm),and the buds enveloped by laminated membrane were also observed All the granules and small buds of early stage endogenous vesicle that either arose from or embeddedin in the internal surface of exogenous vesicles were found The general character of the polycystic echinococcus collected from the gerbil in Inner Mongolia is similar to that of Echinococcus vogeli which is the pathogen of polycystic hydatid disease and has only been reported in Central America and South America,but is distinguished from it by the structure and morphology of its primary exogenous vesicle,the primary exogenous vesicle of larval Echinococcus vogeli Rausch et Bernstein,1972 has a large plaque from which have arisen the flattened primary vesicles,prior to onset of exogenous proliferation (Rausch and D'Alessandro,1999) Since the life history of this new metacestode is not known,it is tentatively named Polycystia neimonguensis sp nov
