VERMES 



159 



suckers enabling it to hold fast in the mucous coat of the 

 canal, while its body, called strobila, lies free in the intestine. 

 The segments of the body, narrow and short near the head, 

 increase in size posteriorly and may number as many as 

 one thousand. They are known as proglottides. It has 

 no alimentary canal and no blood system, the nourish- 

 ment being absorbed through the body wall. The nervous 

 system consists of two small ganglia in the head and a 

 nerve cord extending from them along each side of the 

 body. Each of the segments in the posterior half of the 

 adult worm contains both male and female organs of 

 reproduction and 

 each segment 

 near the end has 

 more than a thou- 

 sand mature eggs. 

 From time to 

 time a segment 

 is broken off and 

 passes to the ex- 

 terior where if 

 through water or 

 otherwise the eggs 

 within it reach 

 the alimentary 

 canal of the cow 

 further develop- 

 ment ensues. 



The young migrate from the digestive tract of the cow to 

 the muscles and form a cyst or sac in which stage it is 

 known as a bladder worm or cysticercus. This is the larval 



FIG. 185. A piece of pork containing several cysti- 

 cerci (larvae) of a human tapeworm (Tsenia soliurri). 

 Photograph natural size. 



