PARASITISM 



173 



In the uterus there develops in this egg a six-hooked embryo. As the 

 proglottid becomes ripe and passes out of the body of the host with the 

 feces, it carries with it thousands of embryos, still inclosed in the egg 

 shells. 



2. If this proglottid falls upon vegetation and is eaten by a cow, the 

 eggs are freed from the proglottid in her intestine and the embryos escape. 



Fig. 81. — Diagram showing the life history of Taenia saginata. A, the egg. X 550. 

 B, egg containing six-hooked embryo. X 550. C, young eysticercus. X 30. D. 

 cysticercus showing beginning of the papilla. X 30. E, the papilla showing an early stage 

 in the dovelopment of the seolex. X 30. F, the papilla containing the scolex. with suckers 

 and rostellum. The latter has rudimentary hooks, which later disappear as the rostelluni 

 is retracted into the scolex. X 40. G, the scolex and neck everted but still attached to 

 cyst. X 3. (All from Leuckart, " Parasiten des Menschen") 



They bore their way through the wall of the alimentary canal and, 

 migrating through the tissues, reach the voluntary muscles, especially 

 the muscles of mastication, where they become encysted. 



3. The encysted larva in from three to six weeks develops a bladder- 

 like sac filled with a clear watery fluid and so becomes a bladder worm, 

 or eysticercus. One side of the wall of this sac gradually becomes thick- 

 ened, is inverted, and forms a hollow papilla projecting into the sac. 



