THE LIVER-FLUKE. 39 



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

 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 mature or 

 nearly mature fluke is released. It then passes into the 

 duodenum, finally entering the liver, where it grows and pro- 

 duces countless numbers of eggs. 



The diagram (fig. 9) on page 40 shows perhaps more clearly 

 the life-history of this all-important pest. 



The symptoms of the disease 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 

 usually commences thirteen weeks after infection, and during 

 the months of November and December. Eapid fattening of 

 the diseased sheep, fever, and quickening of breath are com- 

 mon symptoms at this stage. Death may now result from 

 apoplexy. The third period is marked by a rapid loss of flesh, 

 which usually manifests itself about January. Diarrhoea and 

 jaundice occur now, and either death ensues or there is a spon- 

 taneous recovery. The last period is that of the emigration, 

 when the flukes are all mature and all the ova have been passed 

 out, the sheep then recovering. 



Generally, according to Neumann, flukes remain in their host 

 from nine to fifteen months. 



Effects on the livei: — When invaded the liver becomes thick 

 and soft, and the surface is rough instead of smooth. Inflam- 

 mation sets in, and a dark serous fluid is found in the abdomen. 

 The biliary canals become thickened and much enlarged. The 



