Mother and daughter sporocysts and xiphidiocercariae of Cephalogonimus americanus develop in the snails Helisoma antrosa and H. trivolvis. Following emergence, cercariae penetrate tadpoles in which they encyst. Cephalogonimus americanus develops in the anterior small intestine of Rana clamitans which acquires the parasite by eating infected tadpoles. It is suggested that young frogs may also become infected during metamorphosis.