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 ohtusipes, a coarse-shelled, chestnut- 

 colored crab about one and a 

 half inches in diameter, and 

 P. (IcJiaanii, a slightl}^ smaller 

 species, gra3'ish 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- 



Fio. 72. A common frosh-water crab Other implicated spCcieS, 

 o( Japan Eriochcirjapo,ncu|^^which serves Eviocheir jaVOniCUS (Fig. 72), 

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



IS abundant m all plams 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. 



Mij^airi has shown that in Korea another crab, Astacus japonicus, 



is the intermediate host. 



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



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



Fio. 73. A, encysted ccrcaria of human lung fliiko, 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 cercarite are nearly round, 

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



