DISTOMUM. 14I 
unite at the level of the posterior sucker to form a seminal 
vesicle. In front of the seminal vesicle lies the protrusible 
_ penis 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 
duct. There may possibly be self-fertilisation.* 
The small ovoid eggs (about +2, inch in length) accumu- 
late in the oviduct and are enveloped in hard shells. They 
ate discharged down the bile-duct into the 
intestine and thence to the exterior. The 
eggs, which are laid in the neighbourhocd of water, hatch 
by detaching a circular cap and set free a small ciliated 
larva not unlike an adult in shape. 
Development. 
Fig. 73.—DEVELOPMENT oF DisromMuM HEPATICUM. 
A, Ciliated Larva; B, Sporocyst with contained embryos ; C, Limneus 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 few hours, and if successful during that 
time in finding a water-snail (Zimncus truncatulus ), it is said 
to rotate rapidly with its pointed anterior end against the 
body of the snail and bore its way therein. In the tissues 
of the snail it loses its cilia and grows to about five times 
* A small duct leads dorsally from the median vitelline duct to the exterior. It 
is called Laurer’s duct, and its use is not definitely known. 
