Sub-family. Opisthorchiinæ, Looss, 1899, emend. auctor.
Opisthorchiidæ in which the excretory pore is terminal. Excretory bladder long, dorsal to testes. Uterine coils not overlapping gut forks. Genera: Opisthorchis, Paropisthorchis, Clonorchis, Amphimerus, etc.
Sub-family. Metorchiinæ, Lühe, 1909.
Opisthorchiidæ in which the excretory pore is ventral. Excretory bladder short, ventral to testes. Uterine coils partly overlapping gut forks and extend anteriorly beyond the sucker. Vitellaria compressed on the sides of the body. Genus: Metorchis.
Family. Dicrocœliidæ, Odhner, 1910.
Ovary behind testes. Testes behind the ventral sucker, between it and the ovary. Body thin and transparent. Cirrus sac encloses the pars prostatica and seminal vesicle. Skin smooth. Gut forks do not reach posterior end. Receptaculum seminis and Laurer’s canal present. Vitellaria, moderate, lateral in mid-body slightly overlapping the gut. Uterus with an ascending and descending branch and numerous transverse coils extending to hind end. Eggs dark brown, 25 µ to 60 µ. Excretory bladder tubular in posterior third or half of body. Parasitic in bile-ducts of mammals and birds. Genus: Dicrocœlium.
Family. Heterophyiidæ, Odhner, 1914.
Ovary in front of testes. Genital pore behind or on a level with ventral sucker. Genital pore surrounded by a pseudo-sucker (i.e., its muscle is not sharply separated from but blends with the body muscles). Cirrus sac absent, consequently vesicula seminalis and pars prostatica lie free. Vagina and ejaculatory duct unite into a common duct before opening. Small and very small forms. Body covered with scales. Genera: Heterophyes, Metagonimus, etc.
Family. Troglotremidæ, Odhner, 1914.
More or less flattened Distomes of compact form, 2 to 13 mm. long. Ventral surface flat or somewhat hollowed, dorsal surface arched. Skin completely covered with pointed spines. Musculature weakly developed also in the suckers in those forms that inhabit cysts. Gut with pharynx and a not very long œsophagus and cæca, which end more or less shortly before the hind end. Excretory bladder Y-shaped or tubular. Pars prostatica and seminal vesicle always distinct. Testes elongated, symmetrically placed in or behind the middle of the body. Ovary directly in front of the testes, right-sided, generally much lobed. Receptaculum seminis and Laurer’s canal present. Vitellaria generally well developed, exclusively or for the most part confined to the dorsal surface, leaving only a median band unoccupied. Uterus either very long, coiling here and there, or shorter and more convoluted. Eggs in first case small 17 µ to 25 µ, in the second much larger 63 µ to 85 µ or even 120 µ (?) long. Parasitic in carnivora or birds, generally occurring in pairs in cyst-like cavities. Genera: Paragonimus, Pholeter, Collyriclum, Troglotrema.