This investigation reports for the first time the establishment of a trematode life-cycle in the laboratory using in ovo cultivation of the adult stage. Microphallus primas metacercarial cysts were removed from Carcinus maenas crabs and chemically excysted. Using a modification of the technique developed by Fried (1962) the released metacercariae were grown in fertile hen's eggs to ovigerous adult flukes. These were removed from the under surface of the chorio-allantoic membrane of chick embryos 5 days post-infection and the fluke eggs recovered were used to infect laboratory-reared Hydrobia ulvae snails. When challenged against parasite-free crabs the cercariae released from the experimentally infected snails gave rise to metacercarial cysts that were again identified as M. primas.
