FIG. 54. A series of diagrams illustrating the life cycle in the LIVER FLUKE (Dis- 

 tomum). After Thomas, Leuckart, and others. A, egg in its case; B, early embryo, 

 still in case; C, free-swimming ciliated embryo; D, same after encysting in tissues of snail 

 (sporocyst) ; E, sporocyst at later stage producing by internal, non-sexual processes, 

 new sporocysts, and redice (r) which break from the sporocyst and lead an independent 

 life of their own in the tissues of the snail ; F, a mature redia producing within itself 

 new generations of rediae, and a new type of larva, cercaria which escape by a birth-pore 

 (b.p.) and make their way into the water; G, cercaria; H, same after losing its tail and 

 becoming encysted; 7, the young fluke in the liver of the sheep, where it becomes sexually 

 mature and produces perhaps 500,000 new eggs. b t brain; b.p. t birth pore; c, cercaria; 

 c.m., cell masses, embryos formed non-sexually within sporocysts and rediae; e, eye- 

 spots; ex., excretory tubules and pore (only the posterior portion shows); g, gut; m, 

 mouth; ph, pharynx; r, redia; s, suckers; sc, sporocyst; +, stages in which non-sexual 

 reproduction occurs; *, stage at which sexual reproduction occurs. 



Questions on the Figures. In which stages are eyespots found? 

 Number and position of the suckers? In which stages found? 

 What is the result of increasing the points at which reproduction 

 occurs in the cycle? Is this a combination of metamorphosis and 

 alternation of generation ? Your reasons for your answer ? Compare 

 this with the life history of the tape-worm. Note the encysted 

 stage by which it passes from water to its host in each instance. 



