49 4④ 4c Metacercariae on water plant ingested by humans Sporocysts Rediae or pigs,causing infection Free-swimming cercariae in snail tissue Snail 姜片虫生活史 ⑦ Excyst in duodenum Miracidia hatch. penetrate snail ②Embryonated eggs in water △=Infective Stage 8 Adults in =Diagnostic Stage Unembroynated eggs passed in feces small intestine 吸虫生活史吸虫生活史