FLATWORMS, ROUNDWORMS, AND ROTIFERS 



05 



-m 



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 speak, 



namely, the flukeworm and tapeworm. 

 Flukeworm. — This worm has a flattened, 



leaflike body (Fig. 29), from three fourths 



of an inch to two inches in length. It is 



parasitic in the livers of sheep and cattle, 



especially the former, and causes the dis- 

 ease known as Ziver rot. It exists in 



this country, but is especially preva- 

 lent in England, and causes the loss of 



many sheep there annually. The adult 



worm has two suckers at the anterior 



end of the body for attachment to its 



host. While in the liver of the sheep the 



worm lays great numbers of eggs which 



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

 the outside world. If an egg falls on 

 damp herbage or in water there hatches 

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

 This embryo swims about in the water 

 until it finds a certain species of snail. It 

 then actually bores its way into the body 

 of the snail, and after undergoing compli- 

 cated changes -transforms to an elongated 

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

 time, there are formed within the redia 

 certain bodies called cercarice. Each cer- 

 caria, which is provided with a long tail, 



eventually escapes from the redia and forces its way 



Fig. 29. — Civer 

 flukewoiin ; m, 

 mouth ; r, re- 

 p r o du c t i ve 

 opening; s, 

 sucker. 



Fig. 30. — Embryo 

 of flukeworm. 

 After Thomas. 



hereick's zool. — 5 



