ig6 



FIG. 92. A series of diagrams illustrating the life cycle in the LIVER-FLUKE (Distomum). After 

 Thomas, Leuckart, and others. A, egg in its case; B, early embryo, still in case; C, free-swim- 

 ming ciliated embryo ; D, same after encysting in tissues of snail (sporocysf) ; E, sporocyst at later 

 stage producing by internal, non-sexual processes new sporocysts, and redia. (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, brain; b.p., birth-pore; c, cercaria; c.m. t 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. 



