144 MANUAL OF ZOOLOGY SECT. 



a small animal, such as a water-flea, this may take place 

 "accidentally"; in other cases the intermediate host 

 actually forms the food of the final host. Thus, to give two 

 instances, a Cysticercoid having as an intermediate host an 

 earth-worm is taken with the latter into the enteric canal of 

 a sea-gull its final host ; a Cysticercus which occurs in the 

 liver of rats and mice is received into the enteric canal of 

 the cat. In this way the Cysticercus or Cysticercoid is set 

 free in the enteric canal of the final host; the tape-worm 

 head becomes attached by means of its hooks and suckers 

 to the wall of the intestine, and the long segmented body 

 of the tape-worm is developed behind. 



FIG. 78. Cyst of Taenia echinococcus with the developing daughter-cyst and 

 scolices. (After Leuckart.) 



The commonest human Cestode parasites in the United 

 States and Canada are Tcenia solium and T. saginata ( T. 

 mediocanellata) , the latter being the more common pest. 

 The Cysticercus stage of the former occurs chiefly in the 

 flesh of the pig ; that of the latter in the flesh of the ox ; 

 and the relative prevalence of these two tape- worms in 

 different countries varies with the habits of the people with 

 regard to flesh-eating : where more swine's flesh is eaten 

 in an imperfectly cooked state Tcenia solium is the more 

 prevalent, where more beef, T. saginata. 



