THE ANIMAL KINGDOM 



403 



encysts on a water plant, when the tail is lost. Sheep are 

 infected by eating plants bearing cysts, the contents of which 

 find their way to the liver, where the young animals grow to 

 maturity. Liver rot, the disease produced by this parasite, is 

 often fatal (Fig. 230). 



Fig. 230. Fig. 231. 



Fig. 230. — Stages in the development of Fasciola hepatica. A, miracidium ; 

 B, sporocyst, with rediae developing internally; C, rediae with second generation 

 of rediae and cercariae; D, free cercaria; E, encysted cercaria. (From Van Cleave, 

 Invertebrate Zoology, after Tho?nas.) 



Fig. 231. — A, Taenia solium, the pork tapeworm, s, scolex. B, scolex, 

 magnified. (After Leuckart-Nitsche wall chart.) 



CLASS III. CESTOIDEA. Tapeworms. Endoparasites with 

 two body regions: (1) the scolex, or head, containing hooks or 

 suckers for attachment to the host; (2) the strobila, which is a 

 series of segments, called proglottid^, each of which is provided 

 with both male and female reproductive organs. A mature 

 proglottid is practically filled by the enlarged gonads. Tape- 

 worms inhabit the intestine of vertebrates and live as larvae in 

 the tissues of another animal used as food by the principal host. 



