290 



General Biology 



The adult liver fluke lives in the bile-ducts of the sheep's liver and 

 is continually laying eggs which are carried through the intestine of 

 the host to the outside in the faeces. If these eggs become moist they 



Fig. 179. 



Stages in the Life-History of the Liver Fluke, 

 Distomum Hepaticum. 



1, Egg filled with large vitelline cells in which the segmenting 

 ovum, em., is embedded; o., operculum; 2, Miracidium larva with 

 large ciliated cells, the eyespot e., and the interior papilla, pa. 

 3, Miracidium boring its way into the tissues of Limnaea; f-f., flame 

 cells. 4, a sporocyst containing one fully developed and several de- 

 veloping rediae (R.); e., the degenerate eyes. 5, a redia containing 

 several daughter rediae in various stages of development; m., 

 mouth; ph., pharynx; ent., enteron; r., muscle collar; p., posterior 

 processes. 6, a cercaria; m., mouth; s'., anterior, and s ff ., poster- 

 ior suckers; cs., cystogenous cells. (After Thomas.) 



hatch into tiny ciliated larvae called miracidia. These larvae swim about 

 until they find a pond snail. This found, the larvae bore their way 

 into the snail where a complete change takes place in the parasite. It 

 takes about two weeks for the fluke larvae to form a sac-like sporocyst. 

 Each germ-cell in this sporocyst passes through a blastula and gastrula 

 stage and then becomes a second kind of larva which is now called a 



