Degenerative changes in the reproductive organs of female schistosomes during maintenance in vitro

Degenerative alteration of the reproductive organs of female schistosomes in correlation with the change in egg-laying rate of schistosome pairs in vitro was studied by electron microscopy. The production of normal eggs by adult S. japonicum pairs decreased after 4 days in vitro followed by an increase of abnormal egg laying up to day 8. In S. mansoni, the yield of both normal and abnormal eggs decreased gradually from the start of maintenance in vitro in spite of a much higher pairing rate than in S. japonicum. The vitelline gland of 14-day in vitro-maintained S. japonicum stained with Fast red B, while that of S. mansoni did not. The ovary of both species exhibited regressive features after 14 days of maintenance in vitro. Ultrastructural examination showed that the vitelline cells and oocytes of S. japonicum and S. mansoni had already lost their structural integrity after 2 days in vitro and continued to exhibit signs of structural degeneration throughout the 14-day in vitro maintenance period. The regressive changes in reproductive potential of female S. mansoni maintained in vitro for 4 days could be reversed by surgically implanting the parasites into mouse mesenteric veins.