THE LIVER FLUKE 



367 



little more than a sack (sporosac), in which, by a process of 

 internal budding, a number of new individuals, rediae, are pro- 

 duced. These are slightly more 

 highly organized, but continue 

 the process of internal budding 

 for several generations. Then 

 the rediae, by a similar process, 

 develop a new type of individ- 

 uals called cercariae. These are 

 again a little more complex. 

 They have two suckers, a forked 

 intestine and a tail. The cer- 

 cariae leave the snail and be- 

 come encysted on the grass. 

 If now they happen to be in- 

 gested by a sheep with the grass 

 they are set free from the cyst 

 in the stomach of the host. 

 The parasite may now be called 

 a young fluke, for if it succeeds 

 in finding the opening of the 

 bile duct it works its way up 

 into the liver and then develops 

 directly into the fluke. The 

 mature fluke is well organized 



as far as digestive tract and „ ^, ,• n , ^^ • , 



^ Fig. 231. — The liver fluke, Fasciola 



reproduction systems are con- hepatica, showing the arrangement of 



rprnpH Tlip rpr»rnr]iirti'vp c;vc; ^^^^ reproductive organs. Do, Yolk, 

 cernea. ine reproauctive sys- ^^ vitelHne glands; Dr, ovary; Gp, 



tem especially is very highly ^irr^is sac; 0, mouth; Ov, oviduct, or 



, uterus; S, ventral sucker; Sg, shell 



developed. gland; T, testis; U, intestine; V, 



755. A common Cestode is the vitelline duct. (From Tyson after 

 ' ^^ Sommer.) 



tapeworm. The one common 



in the dog may be taken as a type. The eggs originate in the 



intestine of the dog and reach the earth with the faeces. Either 



