PARASITISM 



171 



200. Life History of the Sheep Liver Fluke. — The following is an 

 epitome of the life history of this liver fluke (Fig. 80) : 



1. The egg cell is produced in the ovary of the fluke and is passed 

 down the oviduct, being fertilized on the way. It becomes enveloped 

 by yolk derived from the yolk glands and chitin-forming material also 



fye sjoof 



Fig. 80. — Diagram of the life history of a sheep liver fluke. A, the fluke. Natural 

 size. B, the egg. X 135. C, the miracidium with cilia, eye spot, and developing germ 

 cells. X 135. D, the sporocyst, containing developing rediae. (C and D from Leuckart, 

 "Parasiten des Menschen.") X 135. E, the redia, with cercariae developing within it. 

 (From Brumpt, "Precis de Parasitologic," after Thomas, and by the courtesy of Masson & Cic.) 

 X 135. F, the cercaria, somewhat modified. {From Leuckart.) X 150. G, the young 

 fluke. (From Borradaile, " Manual of Zoology," after Thomas, and by the courtesy of Oxford 

 University Press.) H, Lymnaea humilis Say, the snail which is supposed to be the inter- 

 mediate host of the sheep liver fluke in the United States. X 1}^. 



received from the yolk glands is hardened into a shell by a secretion from 

 the shell glands (Fig. 77). 



2. The egg passes to the uterus of the fluke and there development 

 begins. 



3. The egg, containing the embryo, passes out of the uterus of the 

 fluke and out of the body of the sheep with the feces, by way of the bile 

 ducts and intestine. 



