68 



FLATWUR.MS, KoUMJWOKM.S, AND ROTIFERS 



of mature eggs have been given off from the body. The 

 eggs are carried away into ditches and waste place.s, whei-e 

 they may f)e eaten f)y pigs. The embryos 

 soon hatch from the eggs in the intestines 

 of the pigs, and immediate])' bore tlieir 

 way tlu'ougli the tissues to the muscles of 

 tire animal. In this situation the embryo 

 changes into a flask-shaped form, known 

 as the larva (Fig. 35). The presence of 

 these laival tapeworms in the nuiscles of 

 the pig give to the ptjrk an ai-ipearance 

 that causes it to Ije kno\^m as "measly 

 pork." Wlien such pork is eaten raw or 

 insufficiently cooked, the larvoe soon de- 

 velop iido nrature ta.pewornis in the di- 

 gestive tract of man. 

 is best to cook ]iork thoroughly lief ore eating it, 

 although tapeworms ai-e U(jt usualh' fatal to life. This rule 

 of prevention also applies to the beef tapeworm. 



Fig. 3.5. — Lai\'i 

 of tapeworm. 



It 



Roundworms 

 On the whole the members of this group are more worm- 

 like than the flatworms. Their liodies are, in general, 

 cylindrical Ixit misegmented. ;\Iany of the roundworms 

 are parasitic. Perhaps the small worms so often seen in 

 strong vinegar and known as "vhicgar eels" are the most 

 famiUar examples of the roun(hvorms. The nematode 

 worms that live in soil and attack the roots of certain ]ilants, 

 causing galls to form on tlie roots, a.re also more or less 

 familiar. To fliis gi'ou]) also belong the so-called "hair 

 worms," or "lln-ead worms" (Fig. ;-!6). These long slender 

 wrms are often found in drinking troughs ami; so much 



