ANIMAL PARASITES 249 



such as warm, moist surroundings, the ova or eggs hatch and the 

 ciliated embryos become freed. The embryo next penetrates 

 into the body of certain snails and encysts. The sporocyst, as it 

 is now called, develops into a third generation known as redia 

 which escape from the cyst. The daughter redia or cercaria, 

 as they are now termed, leave the body of the snail and finally 

 become encysted on the stems of grass, cresses and weeds. When 

 taken into the digestive tract of the animal grazing over in- 

 fested ground, the immature flukes are freed by the digestive 

 juices. They then pass from the intestine into the bile ducts. 

 The period of development varies from ten to twenty weeks; 

 each sporocyst may give rise to from five to eight redia and each 

 redia to from twelve to twenty cercaria. 



Fluke diseases occur among animals pastured on low, wet, 

 undrained land. Drying ponds and lakes are the homes of the 

 fresh water snails, and in such places there are plenty of hosts 

 for the immature flukes. Wet seasons favor the development of 

 this parasite. Cattle and sheep that pasture on river bottom 

 land in certain sections of the southern portion of the United 

 States are frequently affected with fluke diseases. 



The symptoms of liver rot of sheep may be divided into two 

 stages. The first stage is marked by increase in weight and 

 improved condition. In the second stage of the disease, the 

 animal shows a pale skin and mucous membrane, dropsical 

 swellings, loss of flesh and weakness. The character of the 

 symptoms of the disease depends on the age of the animals and 

 the care that they receive. Young, poorly cared for animals 

 suffer severely from the 'disease, and the death rate is usually 

 heavy. The finding of fluke ova in the ficces is conclusive evi- 

 dence of the nature of the disease. It may be advisable to kill 

 one of the sick animals, and determine the nature of the disease 

 by a post-mortem examination. 



The treatment is preventive. Drainage water from a pasture 

 infested with snails harboring immature flukes is a source of 



