FLATWORMS, ROUNDWORMS, AND ROTIFERS 



66 



and usually taper to the posterior end. They have two 



eyes on the upper surface of the body at 



the anterior end. It is of the parasitic 



flatwornis that we wish especially to si)eak, 



nanicl.v, the flukeworni and tapeworm. 

 Flukeworm. — This worm has a flattened, 



leafiike body (Fig. 29), from three fourths 



of an inch to two inches in length. It is 



parasitic in the livers of sheei^ 'inc^ cattle, 



especially the former, and causes the dis- 

 ease known as liver rot. It exists in 



this comitry, Ixit is especially preva- 

 lent in England, and causes the loss of 



many sheep there annuall}'. The adult 



worm has two suckers at the anterior 



end of the Ijody for attachment to its 



host. Wliile in the liver of the sheep the 



worm lays great numl^ers of eggs which 



find their way to the intestines of the host and thence to 

 the outside world. If an egg falls on 

 damp herl)age or in water there hatches 

 from it a minute, ciliated emljryo (Fig. 30). 

 This embryo swims aliout in the water 

 until it finds a certain species of snail. It 

 tlien actually liores its way into the body 

 of the snail, and after undergoing compli- 

 cated changes transforn;s to an elongated 

 body called a redia (Fig. 31). After a 

 time, there are formed within the redia 

 certain fjodies called ccrcaricc. Each cer- 

 caria, which is provided with a long tail, 



eventually escapes from the redia and forces its way 



Fk 29 — Li\er 

 flukewo.'m; 7>i, 

 nuiuth; r, re- 

 p r (J d u c t i V e 

 opening; s, 

 sucker. 



Fig. so. — Emliryo 

 of flukeworm. 

 After Thomas. 



herrick's zool. — 5 



