[Transmission electron microscopic observation on gonad of Oncomelania hupensis offspring bred in Weishan Lake areas].

Following breeding for 12 winters in the Weishan Lake, the 12th-generation snails fail to fully adapt to the natural environment in northern China, and the remarkable changes in the ultrastructure of the snail gonad may be a cause of gradual decline and even extinction of in the Weishan Lake areas.