[Illustration: FIG. 154.--_Opisthorchis pseudofelineus_: from the bile-duct of the cat (Iowa), _m._, oral sucker; _p.b._, pharyngeal bulb; _es._, œsophagus; _i._, intestine; _va._, vagina; _g.p.m._, male orifice; _ac._, ventral sucker; _ut._, uterus; _v.g._ vitellarium; _s.g._, shell gland; _v.dt._, vitelline duct; _ov._, ovary; _r.s._, receptaculum seminis; _L.c._, Laurer’s canal; _t._, testis; _ex.c._, excretory bladder; _ex.p._, excretory pore. (After Stiles.)] Unfortunately, nothing much is known of the history of the development of _Opisthorchis felineus_; we only know that when deposited the eggs already contain a ciliated miracidium, which, however, according to my experience, does not hatch out in water, but only after the entry of the eggs into the intestine of young _Limnæus stagnalis_; no further development, however, occurs. Winogradoff states that he has seen the miracidia hatch after the eggs had been kept in water for a month at 37° C.; and has even observed free miracidia in the bile of man and of a dog respectively. Although the whole post-embryonal development of the cat fluke remains yet to be investigated, Askanazy by a series of experiments on cats and dogs has discovered the mode of infection. The intermediate hosts are fish, and mainly the ide, in this country called Tapar (_Idus melanotus_, H. and Kr.), and of subsidiary importance the roach (_Leuciscus rutilus_). Both species of fish as well as others are readily eaten raw by man on the Courland lagoon (Baltic). It is, moreover, significant that those persons whom Askanazy found infected with the cat fluke were also infected with _Dibothriocephalus latus_, the intermediate host of which is also fish (Lota sp., Esox sp., Perca sp.). In one of his nine cases Winogradoff also saw a small fluke covered all over with spines, which he conjectured to be the young stage of _Opisthorchis felineus_; as, however, according to my experience, this species, even in smaller specimens, is always without spines, the above hypothesis cannot be accepted. It is much more probable that one of the other species that also invade the liver of cats may accidentally be introduced into man; we know, in fact, that _Metorchis albidus_, Braun, and _Metorchis truncatus_, Rud., are both covered with spines. As, however, the spines of the first-named species are rather apt to fall off, and also as it possesses a different shape (spatula-shaped), it may be assumed that probably Winogradoff had found _Metorchis truncatus_, Rud., 1819, in his patient. Genus. *Paropisthorchis*, Stephens, 1912. Structure as in Opisthorchis, except that the ventral sucker and genital pore occur on the apex of a process or pedicle projecting from the anterior portion of the body. This process is about 1/2 mm. long, and is retractile. *Paropisthorchis caninus*, Barker, 1912.