UNSEGMENTED WORMS 



Fig. 92. 



197 



Fig. 92. A series of diagrams illustrating the life cycle in the Liver-fluke (Fasciola). After 

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

 ming ciliated embryo {miracidium); Z?, same after encysting in tissues of snail {sporocyst); E, sporo- 

 cyst at later stage, producing from parthenogenetic ova redi(B (r) which break from the sporo- 

 cyst 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, cercarim, 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; /, the young fluke in the liver of the sheep, where it becomes sexually mature and pro- 

 duces perhaps 500.000 new eggs, b, brain; b.p., birth-pore; c, cercaria; cm., cell masses; e, eye- 

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

 pharynx; r, redia; a, suckers; sc, sporocyst. 



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? 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. 



