NEBEIS 



193 



of regeneration, so that every piece into which a worm is cut 

 will reproduce an entire one (Fig. 188). 



Other flatworms are parasitic, such as the liver-fluke of the 

 sheep (Fig. 189). This destructive parasite has a complicated 

 series of stages to go through before 

 it becomes adult. Thus the flukes 

 in the liver of the sheep produce 

 eggs which develop into eml)rj'os. 

 These embryos get out of the liver 

 into the food canal, and thence to 

 the exterior. If they are deposited 

 near a pool of water, they may 

 develop further; otherwise thej^ 

 must die. In the water a ciliated 

 larva ^ hatches from each egg, swims 

 about for a time until it finds a 

 fresh-water snail, bores into it, and 

 encysts itself there. In this en- 

 cysted stage the worm is known as 

 a " sporoc3'st," because it is full 

 of germs (spores) of a new genera- 

 tion.- The spores develop in the 

 snail into curious organisms, a sort " 



~ 111 1- ., Fig. 187. — Spcoies of tresh-watcr 



of secondary larva known as redia.' punaria. i, Dendroccelum 



The redia; may ]iroduce, by a kind 



of internal budding, new redise, and 



so on repeatedh', until at last, on the 



death of the snail, or from some other cause, the last generation 



of rediae produces liver-flukes.* The young liver-flukes wriggle 



iF'ig. 190, A. Tig. 190, B. = Fig. 190, C. 



' These, while young, have tails, and are called " cercaria," Fig. 190, D. 



%l 



lactcuni, cream color ; 2, Pla- 

 naria maculata ; 3, head end 

 of same to show light streak. 

 After Woodworth. 



