Fishes are chordates and roundworms belong to the phylum Aschelminthes. In these two organisms, the sexes are separate hence self-fertilization is not possible. Earthworms are hermaphrodite as both the sexes are present in the same body. Earthworms still do not show self-fertilization as the maturing times of both the sex organs are different. In earthworms, the male gonads mature earlier than female gonads. This is known as a protandry condition. Thus it shows cross-fertilization. In liver fluke both cross and self-fertilization is seen as they are hermaphrodites. It shows both the sex organs and thus self-fertilization is commonly seen.