i88 



LEISURE-TIME STUDIES. 



complexity of their development, and for the consequent 

 limitation of their increase, these parasites would overrun 

 and exterminate their hosts in a short period of time. A 

 common tapeworm begins life as a minute body, set free 

 from its coverings and investments, and provided with a 

 special boring apparatus, consisting of six hooks. This little 

 creature will perish unless it can gain access to the body of 



some warm-blooded quadru- 

 ped, and the pig accordingly 

 appears on the scene as the 

 most convenient host for the 

 reception of the little embryo. 

 But within the body of the 

 pig there is not the slightest 

 possibility of the little embryo 

 becoming a tapeworm. The 

 pig has merely to perform the 

 part of unconscious " nurse," 

 and to prepare its "guest" for 

 a yet higher stage of existence. 

 Being swallowed by the pig, 

 the young parasite bores its 

 way through the tissues from 

 the digestive system to the 

 muscles of the animal, and 

 there develops around its 

 body a kind of bag or sac. In 



this state it represents the " cystic worm " of old writers and 

 occasionally it may prefer the liver, brain, or even the eye of 

 its first host to the muscles in which it usually resides. Here, 

 however, it can attain no further development. If the pig 

 dies a natural death, there can be no possibility of the tape- 

 worm stage being evolved. But if, as is most likely, the pig 

 suffers death at the butcher's hands, the little cystic 

 worms may be bought by mankind at large along with the 

 pork in which they are contained. Such persons as par- 

 take of this comestible in an imperfectly cooked condition, 



FIG. 19. Common tapeworm (Teenia 

 ^ soliujii). i. The head, magnified, 

 showing hooks (a), and suckers (/>, c) ; 

 d, the neck, with immature joints. 2. 

 A joint, largely magnified, showing 

 the branching "ovary," in which the 

 numerous eggs of each joint are 

 matured. 



