44 THE LIVER-FLUKE. 



The sporocyst is an oval body with neither mouth nor anus. 

 Its contents split up into a number of bodies, usually varying 

 from six to eight. These structures, found inside the sporocyst, 

 have been formed asexually by internal gemmation, and are 

 known as Redid; (em). Eagh redia (c) is about J^th of an inch 

 in length. Later the sporocyst bursts and the rediee are released, 

 passing out of the rupture one by one. The rediee (c) still 

 remain in the snail, where they move about in the mantle cavity. 

 They, unlike the sporocyst, are provided with an alimentary 

 canal and mouth (jj/i). Again asexual reproduction comes into 

 play, for each redia gives rise by budding (internal) to a number 

 of tailed creatures, known as Cercarke (r). About fifteen to 

 twenty oercariae are produced from each redia. Tbese little 

 tadpole-like organisms pass out of an unpaired orifice near tbe 

 neck of the redia and swim out of the snail, leading a free life 

 in the .water for a short time. These free forms (d) resemble 

 the adult fluke, only they are much smaller, and are provided 

 with a long tail. Eventually the cercaria anchors itself on to 

 a blade of grass or some water-weed, draws in its tail, and 

 becomes converted into a round cyst. Here this agamous cyst 

 will remain until some sheep comes along and devours it with 

 the grass. On being transferred to the stomach of the sheep 

 or lamb the case of the cyst is dissolved, and the yoimg or 

 immature fluke is released. It then passes into the duo- 

 denum, finally entering the liver, where it grows and produces 

 countless numbers of eggs. 



The diagram (fig. 11) sbows perhaps more clearly the life- 

 history of this all-important pest. 



This parasite occurs over all Europe, jSTorthern Asia, North 

 Africa and Abyssinia, the Canaries, the Faroes, and also in 

 Australia, the Sandwich Islands, and S. jVmerica. 



The symptoms of the ili.'^ease caused by this worm may be 

 noticed in four periods. The first is the period of immigration, 

 when the embryos invade the liver : little or no change is then 

 noticeable in the host. The second is a period of anaemia ; this 



