THE LIVER-FLUKE OF SHEEP. 



743 



while it remains within the infested sheep. The eggs are, however, 

 naturally washed away by the bile into the intestines, and finally pass 

 from the sheep and are distributed with the droppings. If the eggs 

 fall upon wet land, further changes take place during warm weather, 

 and an embryo is formed. Fig. 3 shows a fluke-egg with the em- 

 bryo fully formed within the shell. The body of the embryo is cov- 

 ered with cilia, by the motion of which the young trematode is pi'o*- 

 pelled through the water. Both of the engravings (Figs. 3 and 4) 

 are highly magnified. In swimming, the broader end is directed for- 

 ward, and in its center is a projection, used as a boring-tool. The 

 embryo has very simple eye-spots, which render it sensitive to light, 

 and aid it in finding its future home. When the swimming embryo 

 comes in contact with any object, it feels about, and, if not suited to 

 its wants, starts off again. If the object met with is the snail {Lim- 

 nceus truncatulus), shown in Fig. 5, it at once bores into it. In boring 

 through the shell of the snail, the peg-like projection is extended, and 

 the embryo spins around rapidly by means of the cilia. The natural 

 place for the further growth of the embryo is in or near the lung of 

 the snail, and when once lodged there its eye-spots and cilia disappear, 

 and the body becomes oval in shape. Figure 6 shows the embryo 

 while the changes are taking place. When the changes are completed 

 the animal is called a sporocyst, meaning a sac of germs. The sporo- 

 cysts live at the expense of the snail, and will, in July weather, reach 

 their full growth, -fa of an inch, in a fortnight. Fig. 7 shows a full- 



Fig. 5. 



Fig. 7. 



grown sporocyst, or first generation of the liver-fluke. It contains a 

 number of germs, the lower one of which is ready to hatch out. 

 This is the second generation, and is named reclia, after Redi, the cele- 

 brated anatomist. The young redia, when ready, breaks through the 

 wall of the parent, and the wound thus formed closes up, and the re- 



