HABITS OF FLUKE- WORMS. 



151 



occurring in the liver of a single sheep. At this time it passes 



into the intestine, and thence is carried out with the excre- 



ment. The eggs or flukes in many cases drop 



into pools, ditches, or ponds ; here the cili- 



ated young (like Fig. 99) is liberated, and 



soon the ciliae are absorbed, when it becomes 



inert, and probably soon afterward enters 



the body of a snail (Planorlis, etc.), where 



it transforms into a large sac, and devel- 



ops new larvae in its interior. This sac- 



like larva is called a "nurse/'' " sporo- 



cyst," or, when more highly developed, a 



" redia." The progeny of the redia is 



termed a "cercaria." The cercariae are 



restless, migrating from the bodies of their 



snail-host, and have been known in a few 



instances to penetrate the skin of human 



beings. They are probably more usually 



, , i T .j-, i -i -i -I Fig. 101. Fasciola 



swallowed by sheep and cattle while drink- hepatica, enlarged. ., 



ing or grazing, when snail-shells may be 

 accidentally swallowed. From the diges- Beneden - 

 tive canal of sheep, etc., the cercaria penetrates into the 

 liver, where it probably loses its tail and becomes encysted, 

 after many weeks or even months becoming a sexually ma- 

 ture distome. From the liver it passes out through the 

 liver-ducts into the intestine, and is finally expelled, thus 

 completing its cycle of life (Cobbold). 



Distomum lanceolatum Mehlis differs from Fasciola he- 

 patica in the intestine being simple and forked, while that 

 of the latter is much branched. It has occurred but three 

 times in man, but is not rare in the sheep and ox. It has 

 been detected in Europe in the pig, deer, rabbit, and hare. 

 Two immature Distomes have been found in the human 

 eye, and Cobbold thinks they may both be the young of 

 D. lanceolatum. It is described by Diesing under the name 

 of Distomum ophthalmoMum, is half a line in length, and 

 occurred between the lens and its capsule, appearing as dark 

 spots on the surface of the lens. Distomum crassum Busk 

 and D. heterophyes Siebold have each been only once 



