50 ESSENTIALS OF ZOOLOGY 



removed by digestive processes in the stomach, and the 

 young flukes make their way via the intestine to the liver, 



Embryo Sporocyst Redia 



Redia 

 Papilla 



Eye-spots 



Flame cell -% 



Opening of 

 protonephridium 



Redia 



_ Cercaria 



Miracidium 



Cercaria 



PIG. 21. Development of Distoma hepaticum. The figures in order represent : 

 the embryo in the egg case with remnants of the food yolk ; the 

 free larva, or miracidium (after Leuckart and after Coe) ; the sporocyst 

 formed in the lung cavity of the snail, Limnaea truncatula (after Thomas) 

 the cells budded from the internal wall to form redia, one of which is 

 shown ; a redia from the liver of the snail (after Thomas), showing the 

 formation of a daughter redia and of cercariae ; cercaria, the tailed 

 free stage (after Thomas), which becomes encysted on grass or water 

 plants, losing its tail. 



but whether by the portal vein or by the bile duct is not 

 known. They usually remain in the bile ducts, but they have 



