Page:Tropical Diseases.djvu/906

850 This parasite has been found by Yokaguwa to be widely spread among natives of Korea, Formosa, and Japan, in the intestinal tract. It is believed hitherto to have escaped notice from the resemblance of the egg to that of Clonorchis, and the very small size of the adult. According to Leiper the parasite is common in China, in dogs, and belongs to a new genus, Yokagawa, characterized by absence of ventral sucker and the arrangement of the yolk-glands. He maintains that the genital sucker is highly developed but does not possess the circlet of hooks or " antlers " characteristic of the genus Heterophyes, which in other respects it resembles. This interpretation is opposed to that of Yokagawa, who has observed the specimens in a live state and finds that this large disc represents a displaced ventral sucker, and further, as a result of minute study, on developmental as well as morphological evidence, finds that the genital aperture is situated as a minute slit in the anterior aspect of this ventral sucker. The cercarial stage is passed in fresh-water fish, " ayu " (Pkcoglossus altivelis), of. in length by 0.126ten eaten in the raw state by Japanese. Yokagawa has made an elaborate study of the final developmental phase. The cercariæ have a thin and hyaline appearance, and measure 0.14-0.16 mm-0.1 mm. in breadth. They are found attached to the gills, fins, and tails of the fish, much less commonly in the muscles, indicating that the alimentary route is not the usual mode of infection of the fish. Mice and dogs can be infected with the cercariæ. Yokagawa has shown that the cercariÆ can withstand the action of the gastric juice, but that the hyaline capsule is dissolved by its action. The larva) thus set free develop in the duodenum; they are said to be richly studded with pigment granules. Development is very rapid, and the adult stage is reached in seven to ten days after infection. Y. yokagawa is only 1.1 mm. long by 0.42-0.7 mm. broad, and is covered with small spines; in the general disposition of its organs it resembles Heterophyes (Fig. 195); it is easily the smallest fluke found in man. The egg resembles that of C. sinensis in size, but is regularly elliptical in shape, dark brown in colour, and the shell membrane has a double contour, and measures 0.028 mm. in length by 0.016 mm. in breadth. Y. yokagawa is apparently an innocuous parasite in man, causing at most a catarrhal condition of the intestine canal which it inhabits. Thymol and naphthol are efficient anthelmintics.

Synonym.—Fascioletta ilocana. This parasite was discovered in 1907 by Garrison, who noticed peculiar eggs in the fæces of Philippine prisoners in the prison at Biliprid, in Manila, and subsequently obtained a small number of trematodes from the intestinal canal. Odhner has recently demonstrated a crown cf spines round the oral sucker, and therefore has transferred it to the genus