Flatworms and Roundworms Zll 



the redia (re' di a) (after Redi, an Italian scientist). Redia in turn 

 give origin to one or more generations of daughter redia, after which they 

 form a third type of tailed larva called a cercaria (ser-ka'ria) (Gr. 

 kerkos, tail). The cercaria leave the body of the snail, swim for a time 

 if water is available, and then encyst on grass or other vegetation. If the 

 vegetation is eaten by a sheep, the cyst wall is dissolved by the digestive 

 juices and the cercaria travel to the bile ducts of the liver where mature 

 flukes develop in about six weeks. 



TAPEWORM 



The pork tapeworm lives as an adult in the alimentary canal of man. 

 It has the scientific name Taenia solium (te' ni a; soMi um) (L. taenia, 

 ribbon; solus, alone). A closely related species, the beef tapeworm 



ProqJottid 



SheU 



^ Hooks 



Fig. 182. — Development and life history of the pork tapeworm {Taenia so- 

 lium). A, The anterior part of the tapeworm, showing the scolex with its suckers 

 and hooks, as well as young proglottids; B, mature proglottid with multibranched 

 uterus containing eggs; C, egg with embryonal shell (striped) ; D, larva with 

 three pairs of hooks and without shell; E, cyst stage (shown in section) with 

 scolex inside; F, more advanced stage with scolex everted and the bladder at- 

 tached. Stage F develops into the first stage, thus completing the life cycle. 

 Stages A and B are present in the human intestine; stages C and D in the pig 

 intestine; stage E in pig tissues; stage F, again in human body. 



(which also parasitizes man), is called T. saginata (sagi-na'ta) (L. 

 saginare, to fatten). T. solium has an enlarged scolex (sko' lex) (Gr. 

 skolex, worm) which contains hooks and suckers. T. saginata has no 

 hooks. A large string of linearally arranged parts known as proglottids 

 (pro -glot' id) (Gr. pro, before; glottis, tongue) are attached to the 

 neck. One worm may become several feet long and contain hundreds of 

 proglottids. The latter are formed by budding (strobilization) from the 



