[Findings on the life cycle of Pseudoleucochloridium soricis (Soltys, 1952) in the Pyrenees (author's transl)].

Pseudoleucochloridium soricis develops to the sporocyst stage in the digestive gland of the terrestrial Pulmonate Cepaea hortensis. The cercaria, microcercous in type, is liberated and actively penetrates a second terrestrial pulmonate where development to the free metacercarial stage takes place in the pericardial cavity. Ecologically, the cycle of P. soricis in the Pyrenees, exhibits two characteristics which require particular attention: --the transmission of the parasite to the second host, which, although experimentally possible, and with equal success, in two species of Helicide (C. hortensis and Euomphalia strigella) occurs in the wild preferentially in E. strigella. The differing trophic behaviour of the two molluscs is thought to be the factor responsible for this selection;--the level of infection in shrews appears to be extremely low (never more than 1%) in all sampling areas, a character which contraste with the persistantly high level of infection in the second host (at least 50%). This epidemiological character points to the probable evolution of P. soricis in a definitive host (almost certainly a Bird) which has not yet been discovered.