[Dynamic change of population structure of ].

To understand the successive dynamic change of population structure of during a one-year period, so as to provide the evidence for snail control. A river beach and a ditch infested with snails were selected and longitudinally investigated in the midmonth during one year. The snail survey indices included the survival status, gender, number of whorls, length and width of shell, and gonad development status (measured by the color depth of gonad and the length ratio of gonad to liver), and the monthly snail eggs in the soil were collected and counted simultaneously.