BIOLOGY AND HUMAN WELFARE 



399 



The adult Tapeworm is hermaphroditic and each of the older 

 proglottides contains both male and female reproductive organs, 

 while the terminal 'ripe' ones are almost completely filled with 

 eggs which have already developed into embryos. One by one the 

 ripe proglottides become detached from the worm and pass from 

 the host with the feces. For development to proceed further an 

 embryo must be swallowed by a pig, whereupon it bores through 

 the walls of the animal's intestine, passes to the voluntary muscles 

 and there encysts. In this position it develops into the bladder- 



Rosteilum 

 i 



Hooks — 



Sucker 



-Genital 

 pore 



-Uterus 



Fig. 252. — Tapeworm, Taenia solium. A, Anterior and posterior parts of 

 a specimen about 8 feet long comprising some 900 proglottides. Uteri filled 

 with eggs are shown in the last two proglottides. B, Scolex more highly mag- 

 nified. (From Hegner.) 



worm, or cysticercus, stage. To complete the life history, in- 

 fected meat, insufficiently cooked, must be eaten by Man. If this 

 transfer is successfully accomplished, upon attaining the human 

 digestive tract the parasite gradually assumes the adult form, the 

 scolex becomes attached, and a series of proglottides begins to 

 develop. (Fig. 253.) 



Since Tapeworms which live as adults in Man and the higher 

 animals secure their food by absorbing that of their host, they 

 seriously interfere with nutrition, but larval stages are still more 

 dangerous. Thus, the larvae of a tapeworm (Echinococcus) , which 

 lives as an adult in the intestine of the dog and other carni- 

 vores, form in the brain, liver, etc., of man, pig, and sheep large 



