300 



DISEASES OF THE LIVER. 



in the snail for a longer or shorter time, or passes out of the body of the 

 snail and swims about in the water. After a time it attaches itself to a 

 blade of grass (Fig. 154) or some other object, and forms a cyst around 

 itself with material from the large glands, at the same time losing its 

 tail. It now remains quiet until swallowed by some animal. Then, upon 

 arriving in the stomach — of a steer, for instance— the cyst is destroyed, 

 and the young parasite wanders through the gall-ducts or, as some believe, 



Fig. 156. — Drawing from a iiiicroscoj)ic preparation, showing a haemorrhage in the 

 parenchyma of the Hver caused by the common liver fluke (Fasciola Jiepatica). 

 a, Atrophic hver tissue ; b, round-cell infiltration ; c, a portion of the parasite ; 

 d, haemorrhage. (After Schaper, 1890, PL I., Fig. 1.) 



through the portal veins to the liver, where it develops into the adult 

 hermaphrodite. 



From the above we see that this parasite runs through three genera- 

 tions, namely : 



(1.) Ovum, miracidium, and sporocyst . . . first generation. 



(2.) Redia . . . second generation. 



(3.) Cercaria and adult ... third generation. 



During this curious develoi)ment, which lasts about ten to twelve 

 weeks, there is a constant potential increase in the number of individuals, 

 for each sporocyst may give rise to several (five to eight) rediae, each 

 redia to a larger number (twelve to twenty) cercarise, and each adult to an 



