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.
Syn.: Distoma conjunctum, Lewis and Cunningham, 1872; Opisthorchis noverca, M. Braun, 1903 (pro parte); Opisthorchis caninus, Barker, 1912 (?).
Length varies from 2·75 to 5·75 mm. in preserved specimens, average 3·6 to 5·2 mm. Body uniformly spinose, though as a rule spines are not present on the pedicle. Body slightly concavo-convex, the concavity being ventral. Oral sucker 0·28 mm. Pharynx 0·224 by 0·184 mm. Œsophagus 0·04 mm. Ventral sucker 0·176 mm. in diameter. Pedicle about 1/2 mm. long, may be completely retracted.
Fig. 155.—Paropisthorchis caninus: from the bile-ducts of the pariah dog, India. Acet. v., ventral sucker; Ut., uterus; V. ex. lat., longitudinal excretory duct; V. sem., seminal vesicle; Sem. rec., seminal receptacle; Ov., ovary; V. ex., excretory bladder; Test. l., left testis; Test. r., right testis; P. ex., excretory pore. × 40. (After Stephens.)