The output of cercariae of Fasciola hepatica by Lymnaea truncatula and the distribution of metacercariae on grass

Abstract

It has been demonstrated that under normal laboratory conditions Lymnaea truncatula infected with Fasciola hepatica are not able to shed all their cercarial loads before their death. Cercariae are irregularly released over an extended period and considerable variations (4–1789) occur in their output.Laboratory studies have revealed that the green parts of grass (Dactylis glomerata) are preferred to the brown, dead parts by the cercariae of Fasciola hepatica for metacercariae formation. More cysts are formed on the lower surface of submerged leaves than on the upper surface.There is vertical zonation of metacercariae on grass in water. More cysts occur on the upper parts of submerged grass than on the lower parts.Vertical migration of cercariae after settling does not usually occur before cyst formation.The results are tabulated and discussed and correlated with conditio s in the field.This work was undertaken in the Department of Zoology, University of Bristol, Bristol, under the supervision of Dr H. D. Crofton, to whom I wish to express my gratitude.