DISTOMUM. 



141 



unite at the level of the posterior sucker to form a seminal 

 vesicle. In front of the seminal vesicle lies the protrusible 

 /^^//> along which there runs an ejaculatory duct from the 

 former. Penis and seminal vesicle lie in a cavity called the 

 cirrus-sac. A small prostate-gland encircles the ejaculatory 

 d'j(-t. There may possibly be self-fertilisition.^ 



The small ovoid eggs (about -—-^ inch in length) accumu- 

 late in the oviduct and are enveloped in hard shells. They 

 are discharged down the b ile-ducj into the 

 int^|feinj£^and thence to the exterior. The 

 eggs, which are laiTin the neighbourhood of water, hatch 

 by detac hing a circular cap and set free a small ciliated 

 larva not unlike an adult in shape. 



Fig. 73. — Development of Distomum Hepaticum. 



A, Ciliated Larva ; B, Sporocyst withcontained embryos ; C, Liinnceiis truncatulus 

 (natural size and magnified), the host of the Sporocyst. 



It has an outer layer enclosing a solid mass of cells. 

 There are two small pigment spots which may serve as eyes. 

 It lives actively for a lew hours,"aiB if successful during that 

 time in finding a water-snail (Lim^us truncatulus)., it is said 

 to rotate rapidly with its pointed lanterior end against the 

 body^ae^-the snail and bore its w^ therein. In the tissues 

 of the"STTail it loses its cilia and grows to about five times 



* A small duct leads dorsally from the median vitelline duct to the exterior, 

 is called Laurer's duct, and its use is not definitely known. 



