Adults of alveolar Echinococcus species with different uterine structures were collected from Vulpes corsac in the Hulunbeier Pasture of Northeastern China in 2001. They were Echinococcus multilocularis Leuckart, 1863 (type No. 3, similar to E. m. multilocularis), with vaselike uterus; Echinococcus cf. sibiricensis Rausch et Schiller, 1954 (type No. 1), with pyriform uterus; and Echinococcus sp. (type No. 2) with spherical uterus at segment top. The metacestode development in rodents also differed among those 3 parasites. In the case of E. multilocularis (type No. 3), many germinal cells grew on the inner surface of early cysts, most of which metastasized into host tissue to form brood vesicles or from the germinal cell layer on the inner surface of the vesicle wall. Cells also had an appearance of proliferating by means of alveolar buds from alveolar tissue that developed outward to form new alveolar foci. In Echinococcus cf. sibiricensis (type No. 1), the formation of alveolar vesicles was due to the metastasizing of germinal tissue into host tissue; protoscoleces grew in the center of alveolar vesicles. In type No. 2 (Echinococcus sp.), the formation of the alveolar vesicle was by multiplication of germinal cell layers on the inner surface of alveolar cysts; protoscoleces grew from the germinal cell layer and mesh in the vesicles. On the basis of uterine structure and on differences in development of metacestodes in experimental rodents, we propose that the 3 types of Echinococcus represent 3 independent species: E. multilocularis, Echinococcus sibiricensis, and Echinococcus sp. (type No. 2—as yet under study).