ANIMAL PARASITISM 



763 



tapeworms is usually referred to as segmentation of the body, but 

 it is probably more correct to consider a tapeworm as a linear colony, 

 in which the segments are really individuals in various stages of 

 maturity. 



Taenia solium, the pork tapeworm of man, may be taken as an ex- 

 ample to illustrate the structure and life history of a cestode. The 

 adult tapeworm consists of a scolex or head provided with four mus- 

 cular suckers and a snoutlike rostellum surrounded by a row of 



Head 



flead 



mi 



/Mature serine nis 





/Aature 



Fig. 402. — Common tapeworms, showing different regions of the body. At the 

 left above, scolex of Taenia saginata, beef tapeworm ; left below, proglottids of 

 Monie:sia, sheep tapeworm ; middle, scolex and proglottids of Taenia solium, pork 

 tapeworm ; right, scolex and proglottids of Dipylidium caninum, a dog tapeworm. 

 (Courtesy of General Biological Supply House.) 



chitinous hooks, which serve as means of attachment to the wall of 

 the human intestine; a narrow unsegmenfed neck behind the scolex, 

 and then a series of several hundred proglottids (the segments) be- 

 coming progressively larger as they get farther from the scolex. The 

 whole chain of proglottids is called the stroMlus. New proglottids 

 are constantly budded off from the neck; consequently, the young- 

 est proglottid is the first one back of the neck and the oldest one is 



