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 infested 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 faeces is conclusive evidence 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.

[Illustration: FIG. 71.--Tapeworm larvae in liver (_Echinococcus
polymorphus_).]