128 ANIMAL BIOLOGY 



develops only to a certain stage and does not attain matu- 

 rity until it is taken into the body of some other animal. 

 The bladder worm of one kind of human tape-worm, Tce- 

 nia solium, occurs in the pig where the cysts frequently 

 attain the size of a pea and may become considerably 

 larger. The meat infested with these cysts is called 

 "measly pork," and if such meat is eaten raw by man, the 

 cysts will develop in his intestine into mature tape- worms. 

 The bladder worm of another large species infesting man 



FIG. 1 06. Development of the bladder worm of the tape-worm Tatnia 

 saginata. a, embryo within egg shell; b, free embryo; c, bladder worm; 

 d, same with introverted scolex. (After Leuckart.) 



occurs in cattle and the mature worm is acquired by eating 

 insufficiently cooked beef. 



Human beings may carry the bladder worms in their 

 tissues and the mature worms in their intestine. If a 

 person swallows the eggs of a tape-worm he may get 

 bladder worms in his flesh. These may produce serious 

 injury, especially if they lodge in the brain or some other 

 delicate organ. One case is recorded of a bladder worm 

 lodged in a woman's eye where its growth could be watched 

 for several years. 



While the bladder-worm stage of Cestodes is usually 

 small there are a few species in which it is quite large. In 



