The development of the metacercariae of Microphallus similis in vitro and in the mouse

The development of the progenetic metacercariae of Microphallus similis in the mouse and under a range of in vitro cultivation systems was studied and compared. The flukes began egg production after 24 h in the mouse and by Day 4 post infection large numbers of eggs were present. These eggs began to embryonate in utero and contained a ball of cells; however, subsequent incubation in sea water failed to produce recognisable miracidia. In the majority of culture systems, gametogenesis and vitellogenesis occurred. Large numbers of abnormal eggs of three basic types were produced in vitro; these defects were probably related to the premature tanning of the eggshell precursors within the vitellaria and ducts. Apparently normal eggs were also produced, but they were probably unfertilized since sperm were rarely observed in vitro and they failed to embryonate.