222 



THE FLUKES 



species of crabs in Formosa, and Yoshida, another Japanese in- 

 vestigator, acting on the discovery of his countryman, found the 

 larvae in a fourth species of crab in Japan. The crabs most com- 

 monly infected are Potamon obtusipes, a coarse-shelled, chestnut- 

 colored crab about one and a 

 half inches in diameter, and 

 P. dehaanii, a slightly smaller 

 species, grayish black or red- 

 dish in color. Both these 

 crabs bound in the shallow 

 waters of mountain streams, 

 and the former species is 

 sometimes used as food. An- 



FIG. 72. A common fresh-water crab other implicated Species, 

 of Japan , Eriocheirjaponicus which serves EriocheiT japOUWUS (Fig. 72), 

 as a host for lung fluke. (After Yoshida.) . 



is abundant in all plains rivers 



in Japan and is a common article of diet throughout the country. 

 It is a larger crab, reaching a diameter of three inches, and has 

 large hairy claws. The fourth species, Sesarma dehaani, is of 

 medium size, dark in color with light reddish claws, and inedible. 

 Miyairi has shown that in Korea another crab, Astacus japonicus, 

 is the intermediate host. 



The lung fluke cercarise encysted in these crabs (Fig. 73A) 

 were found chiefly in the liver while young, but when older they 



FIG. 73. A, encysted cercaria of human lung fluke, Paragonimus ringeri, from 

 gill of crab; B, larva emerging from cyst. o. s., oral sucker; int., intestine; ex. v., 

 excretory vesicle; v. s., ventral sucker. X 50. (After Yoshida.) 



occur in the gills. They vary in number from a few to several 

 hundred. In some localities a very high per cent of crabs are 

 infected, Nakagawa reporting that practically 100 per cent are 

 infected in one district in Formosa where the lung fluke is very 

 common. The cysts containing the cercarise are nearly round, 

 0.5 mm. (sV of an inch) or less in diameter, and have relatively 



