38 



BRANCH PLATYHELMINTHES 



four principal trunks extending throughout the scolex and 

 proglottides. 



Multiplication and Development. — Each proglottis, as it 

 matures, becomes hermaphroditic. Since these proglottides 

 are originally developed from the head, the posterior ones are 

 oldest. When filled with embryos, they are detached and pass 

 out with the waste material from the intestine. When taken 

 into the alimentary canal of the hog with its food, the hooked 

 embryos bore through the intestinal wall and into the voluntary 

 muscles, where they grow and 

 continue to develop until they 



Fig. 28 — Tcenia echinococ'cus, en- Fig. 29. — Portion of the intestine 



larged. (Hosier and Peiper.) of a dog infeste(i with echinococcus 



tapeworms, natural size. (Oster- 

 tag.) 



reach the bladder-worm stage, or cysticercus. When pork 

 containing a cysticercus is eaten, unless it has been killed by 

 thorough cooking, the head is everted from the bladder-like 

 covering and is attached to the intestinal wall of the host, 

 where proglottides are rapidly developed. These mature in 

 ten or twelve weeks. 



Species. — There are many species of tapeworms. One form, 

 Tcenia saginata, which occurs in man, is obtained through 

 eating beef cooked rare; another form, Twnia solium,^ already 

 mentioned, from eating pork; and another, Bothrioceph'aliis 



' Tmnia solium is sometimes found in the encysted or intermediate stage 

 in the muscles, eye, or brain of man. The eggs are thought to have been 

 taken into the stomach with lettuce, cress, and the like, which had been 

 watered with liquid manure. 



