Making a study of primipally the Embryonic development of the Metagonimus takahashii and umparing to this the Embryonic development of the Metagonimus yokogawai. Generally the most standing out differences to the periods of development of the Tremastodes embryo are; In the Metagonimus embryo only one shell membrane appears. Having a very close relation to this the so called protect cell of which two cells appear. One large germcell and two gland cells (later unites and becomes one vesicle) appears before the first period of division of any large cell.