[The life cycle of Microphallus gracilis Baer, 1943, a parasite of Neomys fodiens in the Pyrenees. Modalities of the transmission of the Digenea in nature (author's transl)].

Microphallus gracilis develops to the sporocyst stage in the digestive gland of the snail Bythinella reyniesii. The xiphidio-cercaria monostomous, anenterous in type, is liberated in water and actively penetrates a Crustacea Gammarus pulex where it encysts. From the point of view of the transmission ecology, the natural focuses of M. gracilis are composed of two different areas: an area where the parasite multiplies coinciding with biotope Bythinella and an area limited to the length of the river where the parasite spreads.