Six species of monogenia from and five species of fishes have been dealt with. Histology and histochemistry of monogenia P.multae (Chauhan, 1945), commonly encountered on scombroid fishes have been studied. Some aspects of Mehlis gland, ootype complexes have been studied. Adhesive and reproductive effort of some monogenia and digenia have been studied and compared. However there are several parameters to be considered , such as thickness of egg shell, viviparity or oviparity etc. The full significance of these remains to be explored.