PHYLUM PLATYHELMINTHES 



159 



place (4) the vitelline duct brings in and surrounds the eggs with 

 yolk globules derived from (5) the vitelline glands (Fig. 105, Do) ; 

 the shell gland then furnishes a chitinous shell, and the eggs pass 

 on into (6) a tube called the uterus, which leads to the genital pore. 

 One liver-fluke may produce as many as five hundred thou- 

 sand eggs, and, since the liver of a single sheep may contain more 



Fig. 106. — Stages in the life-history of the liver fluke, Fasciola hcpatica. 

 a, miracidium (ciliated embryo), b, sporocyst containing rediae (R). c, a 

 redia; C, cercaria; D, gut; A', germ-cells; R, redia. d, cercaria. (From 

 Sedgwick; b, after Leuckart; c and d, after Thomas.) 



than two hundred adult flukes, there may be one hundred million 

 eggs formed in one animal. The eggs segment in the uterus of the 

 fluke, then pass through the bile ducts of the sheep into its in- 

 testine, and finally are carried out of the sheep's body with the 

 fasces. Those eggs that encounter water and are kept at a tem- 

 perature of about 75 F. continue to develop, producing a ciliated 

 larva (Fig. 106, a) which escapes through one end of the egg-shell 

 and swims about. This larva, called a miracidium, possesses a 



