40 



ZOOLOGY. 



iiig ciliated, while there is a large sucker on the under side 

 of the body. These are called fluke-worms. Fasciola he- 

 patica (Fig. 40) lives in the liver of the sheep, causing the 

 disease known as "rot." It is most abundant in the spring, 

 several hundred occurring in the liver of a single sheep. 

 At this time it passes into the intestine, and thence is car- 

 ried out with the excrement. The eggs or flukes in many 

 cases drop into pools, ditches, or ponds; 

 here the ciliated young is liberated, and 

 soon the ciliee are absorbed, when it be- 

 comes inert, and probably soon afterward 

 enters the body of a pond snail {Limnmuf:), 

 where it transforms into a large sac, and 

 develops new larvEe in its interior. This 

 sac-like larva is called a " nurse,'' or, when 

 more highly developed, a " redia." The 

 progeny of the redia is termed a "cerca- 

 ria." The cercarife are tad])ole-like, and 

 are restless, migrating from the bodies of 

 their snail-host, and have been known in a 

 few instances to penetrate the skin of hu- 

 man beings. They are i)robably more ustt- 

 ally swallowed by sheep and cattle while 

 FiG.io.—Fascioiahe- drinking or grazing, when snail-shells- may 



patica, enlarged. , ■ i ^ it ii n xi i.i t 



a, branched iijtes- be accidentally swallowed. Irom the di- 

 gestive 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 mature fluke-worm. From the liver it passes 

 out through the liver-ducts into the intestine, and is finally 

 expelled, thus completing its cycle of life. 



The tape-worms represent the order of Cestodes. They 

 are large pai-asi tic worms, with no month or digestive tract; 

 the joints are verjy numerous, sometimes over a thousand 

 '71 number. 



The common human tape-worm, Tania solinm, varies 



