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, ditclies, or ponds ; here the cili- 

 ated young (like Pig. 99) is liberated. Its 

 body is spindle-shaped, with a double eye- 

 spot. It is very active, and soon after birth 

 enters the body of a snail (Limnceus), 

 whei'e it transforms into a large sac, and 

 develops new ]arv« 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 cercarise 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 

 swallowed by sheep and cattle while drink 

 ing or grazing, when snail-shells may be 

 accidentally swallowed. From the diges- 

 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- 

 tare distome. From the liver it passes out through the 

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

 completing its cycle of life. 



Distomum lanceulahim 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 loth be the young of 

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

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

 Of'curred between the lens and its capsule, appearing as dark 

 opots on the surface of the lens. Diboomum crassum Busk 

 and D. heterophyes Siebold have each been only once 



- Fasciola 

 hepcSica, enlarged. <(, 

 branched intestine. — 

 From Gervais and Van 

 Beneden. 



