RESUMEN
Attempts to induce acquired resistance in Lymnaea rubiginosa snails against the echinostomes Echinostoma audyi and Hypoderaeum dingeri by means of irradiated miracidia were unsuccessful, although Lie and coworkers using similar methods had recently sensitized Biomphalaria glabrata against Echinostoma lindoense (1975a). In contrast to the B. glabrata-E. lindoense system, in Lymnaea rubiginosa the amebocytic response to irradiated parasites was slow: irradiated E. audyi sporocysts were encapsulated 15 to 28 days and H. dingeri sporocysts 20 to 27 days postexposure. No obvious enlargement of the amebocyte-producing organ was seen. No resistance was demonstrable to subsequent homologous challenge. Development of acquired resistance to a trematode infection in snails may be related to the speed with which the snails destroy the irradiated sporocysts.