Rot in Sheep. 



23 



is provided with a small boring prominence, and as it swims 

 about in the water it searches for a certain species of water 

 snail, to the surface of which it fastens itself, and eventually 

 bores its way into its body. It then becomes the sporocyst. The 

 sporocyst grows slowly within the snail, and eventually the germ 

 cells which it contains produce other organisms called redice> five 

 to eight in number, which eventually escape from the sporocyst 

 and attach themselves to the liver of the snail. Within each redia 

 are formed from 12 to 20 individuals of the next generation, which 

 are known ai* cercariae. These last-named organisms are some- 

 what similar to the adult parasites into which they eventually 

 develop, their bodies being flat and oval in shape, but they are 

 provided with a tail After leaving the redia these cercariae 

 pass out of the body of the snail into the water, where they 

 swim about until they attach themselves to a blade of grass or 

 some other object ; subsequently they lose their tail, become 

 encysted — that is, form a case — and remain quiescent until 

 swallowed by the sheep, in whose stomach the wall of the cyst 

 is destroyed. The liberated parasite ultimately finds its way 

 to the liver of the sheep or other animal, and develops into the 

 adult hermaphrodite fluke. 



The fluke parasite runs through three reproductive generations 

 namely : — 



1st. The sporocyst ; 

 2nd. The redia ; 

 3rd. The adult fluke. 



There is a gradual increase in the number of the organisms 

 derived from each of these generations. For example, 

 the sporocyst containing germ cells gives rise to several 

 (5 to 8) rediae, and each redia to a larger number of cercariae 

 (12 to 20), while it has been calculated that each adult fluke 

 may produce the enormous number of 45,000 eggs. But for 

 this remarkable fertility there would be comparatively small 

 chance of the entire cycle of life of the fluke parasite being 

 completed. 



Symptoms of Rot in Sheep. 



In consequence of the extremely slow development of this 

 disease, the fact that the sheep are affected is scarcely ever 



