PARAMPHISTOMUM DAUBNEYI - THE DEVELOPMENT OF REDIAL GENERATIONS IN THE SNAIL LYMNAEA-TRUNCATULA

Rediae of Paramphistomum daubneyi were counted and measured in Lymnaea truncatula to elucidate the variability in the numbers of free rediae and cercariae occurring between naturally infected snails and experim ental single-miracidium infections. Experiments were performed using o ne miracidium per snail and snail raising was carried out at 20 degree s C. Two redial generations succeeded each other in the snail until da y 49. A mean of 8-10 rediae differentiated in the sporocyst at days 7 and 14; the remaining germ balls and redial embryos decreased in numbe r after day 21. First-generation rediae became free in the snail's bod y starting at day 14 and their number increased to a mean of 7.5 at da y 49, with a maximum of 10 rediae being detected in 1 snail. They prod uced second-generation rediae, which exited from the body starting at day 28, and then cercariae, which exited from day 42 onward. The count of second-generation rediae was 6-6.2/snail at day 49, with a maximum of 12 being detected in 1 snail; they produced only cercariae.