226 



THE FLUKES 



Little is known . of the life history of any species except the 

 Chinese fluke, C. sinensis. The eggs (Fig. 76A) are of charac- 

 teristic shape, and hatch in water into miracidia (Fig. 76B). 

 The encysted cercarise of this fluke (Fig. 77A) have been found 



in the subcutaneous tissues and 

 muscles of 12 different species 

 of fresh- water fish. The cysts, 

 which are very small, measuring 

 only about 0.14 by 0.10 mm. (J|Q 

 by 250 of an inch), are usually 

 more abundant in the superfi- 

 FIG. 76. Egg and ciliated em- cial than in the deeper tissues. 



fish throughout the year, the 

 younger ones are more frequently met with in late summer and 

 early autumn. 



When infecte fish are eaten, according to experiments re- 

 cently made with animals by Kobayashi, the larval flukes escape 

 from the cysts (Fig. 77B) within three hours, and in fifteen hours 

 they may already have 

 reached the bile duct and gall 

 bladder. The parasites reach 

 maturity and eggs are found 

 in the faeces of the host within 

 26 days. The young flukes 

 have a spiny cuticle until 

 nearly mature, but the spines 

 finally disappear. 



Muto recently found cer- 



. 

 Cari88 in the Snail Bythima 



B 



FIG. 77. Larvae of Chinese fluke; A, 

 cercaria encysted in fish; B, larva freed 



striatula var. japonica which frorn c f st; -> mouth in oral sucker : , 



. ventral sucker; ex. v., excretory vesicle; 



encyst in fish Of VariOUS ph., pharynx; int., intestine. 



species. When these fish 



are fed to dogs and mice, infection with Clonorchis sinensis results. 

 On the other hand, controls fed with fish parasitized by cercarise 

 from the snail Melania libertina, which Kobayashi believed to be 

 the first intermediate host, developed infections with Meta- 

 gonimus only. Sporocysts develop in Bythinia about three weeks 

 after infection with the miracidia. 



It is probable that the European liver fluke, 0. felineus, and its 



