226 



THE FLUKES 



Fig. 76. Egg and ciliated em- 

 bryo of Chinese fluke, Opisthorchis 

 sinensis. X 700. (After Katsuradat) 



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

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

 teristic shape, and hatch in water into miracidia (Fig. 7()B). 

 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. (y^,y 

 '\v j^^ of an inch), are usually 

 more abundant in the superfi- 

 cial than in the deeper tissues. 

 Although cysts can be found in 

 fish throughout the year, the 

 younger ones are more frequently met with in late summer and 

 carl 3^ autumn. 



When infected 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 

 the}' 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 daj'S. The young flukes 

 have a spiny cuticle until 

 nearly mature, but the spines 

 finally disappear. 



The first intermediate host Fig. 77. Larvae of Chinese fluke; .1, 



• , 1 • u 1 1 . 1 1 •!• eercaria encysted in fish; B, larva freed 



mtO which newly hatched Clll- f^om cyst; m.. mouth in oral sucker: V. s.. 



ated embryos penetrate is not ventral sucker; ex. v., excretory vesicle; 



,-11 ± 1 A ph., pharvnx; int., intestine. 



certamly known yet, but 



Kobayashi believes it is one or more of the several species of snails 

 of the genus Melania, especially Melania libertina. These snails 

 have been found to harbor cercarise which bear a distinct resem- 

 blance to the young encysted larvae of the Chinese fluke, and they 

 are abundant in rivers and swamps of regions where the liver 

 infection prevails. 



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

 Indian and American allies all have histories very similar to that 



