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THE POPULAR SCIENCE MONTHLY. 



sage of the creature from one animal or host to another. The eggs 

 are swallowed by some animal, usually a vegetable feeder, they hatch 

 within its body, enter its tissues, and remain in a state of incomplete 

 development until transferred to the stomach of another animal which 

 has eaten the flesh of the first one. Here development recommences, 

 and goes on to completion, when the process of reproduction begins. 

 Each species of worm has its particular animals, through the agency 



of which these changes occur, and, if in 

 its passage it gets ofi" the proper track, 

 that is, enters the wrong animal, it must 

 either perish, or, as sometimes happens, 

 find its way by a second transfer into 

 the body of its destined host. The tape- 

 worm of man. Taenia solium (Figs. 23 and 

 24), is a member of this group, belonging 

 to the Cestoidea, or ribbon-like worms. 

 These cestoids a,re found in all classes of 

 vertebrate animals. They exist in two 

 principal forms. The first or vesicular 

 form resembles somewhat in appearance 

 the finger of a glove partly drawn in- 

 ward. In this shape they are always 

 lodged in the midst of the flesh, or in a 

 closed organ, surrounded by a cyst, and 



Fis. 23. TAENIA Solium, or Solitary 

 Worm. 

 a, head, or scolex : b, tape formed of many 

 individuaJs, tne last of which, com- 

 pletely sexual, separate under the 

 name of Proglottides, and represent 

 the adult and complete animal. Each 

 solitary worm is a colony. 



Fig. 24. a, Rostellum; 6, Crown of Hooks; c c. 

 Suckers. 1. Scolex of the Tcenia solium. 2. 

 Hooks expanded ; a, Heel of the Hook. 



thus circumstanced the worm is harbored by a host which is to serve 

 as a vehicle to introduce it into its final host. It is a parasite on a 

 journey, and usually bears the name of Cysticercus (Fig. 25). In the 

 second shape it is like a ribbon, it attains a great length, always occu- 

 pies the intestine, and is mainly occupied in producing eggs, which it 



