188 PARASITOLOGY. 



pores irregularly alternate ; the ripe segments are 

 nearly twice as long as wide. The worm usually 

 attains the length of two to three feet. 



Life Cycle, — The ripe segments from the small in- 

 testines of the dog pass out to the ground with the 

 feces ; these segments soon decompose and myriads of 

 ova are liberated which become desseminated in food 

 and water. The intermediate host is sheep which 

 become infested through contaminated food or water. 

 The ova, upon reaching the stomach, hatch into six- 

 hooked embryos which immediately begin to migrate 

 through the tissues, or they may penetrate an artery 

 and be carried by the blood current ; the embryos 

 will develop only in nerve tissue, and may be 

 carried to these centers through the blood stream ; 

 if lodged in tissue, not nerve, they perish, but if 

 lodged in the brain or spinal column they begin their 

 transformation into the hydatic state ; in eight or 

 nine days after the ova are ingested the embryos 

 have reached the brain and in twenty days are about 

 one-tenth inch in diameter; development continues 

 and they are fully developed in ninety days. The 

 cysts possess a hydatic and germinal membrane ; 

 from this inner or germinal membrane there is devel- 

 oped from one to two hundred heads or larva. The 

 encysted larva is called Coenurus Cerebralis or 

 Cysticercus Coenurus. They may develop in the 

 coverings of the brain or spinal cord or in the brain 

 and cord substance ; if the dog eats these cysts, 

 through digestion the larva (which consists of ahead 

 provided with four sucker discs and a rostellum of 

 booklets and a neck) is liberated and fixes itself 

 to the mucous membrane of the small intestines and 

 develops into the mature worm in two months. 



