112 



SYSTEMATIC ZOOLOGY 





CLASS III. CESTODA 



The Cestoda (Gr. /ceo-ros, a girdle) are known commonly as 

 the tapeworms, from their usually elongated, bandlike bodies. 

 They are all parasitic in the alimentary canal of vertebrates, and 

 while some resemble greatly the Trematoda, they can always be 

 distinguished by the absence of an alimentary canal or digestive 

 system, the food passing from the alimentary canal of the host 



Fig. 102. Development of tapeworm. A. six-hooked embryo; B, proscolex of Tcsnia 

 saginata, the beef tapeworm ; C, D, E, successive stages in the formation of the scolex of 

 the same ; F. I: oped cysticercus or bladder-worm of T. solium, the pork tapeworm ; 



G, scolex of T. serrata with remains of the vesicles of the cysticercus; H, young tape- 

 worm of 7. serrata. (After Lcuckart, from Parker and Has well's Manual.) 



directly through the body wall of the parasite. The simplest 

 Cestoda have no organs for attaching themselves to their h 

 and their bodies consist of a single piece ; they are parasitic for 

 the most part in various fishes and water birds. The more com- 

 plex and by far the greater number of the Cestoda are provided 

 with an organ of attachment called the head, or scolex. This is 

 usually furnished with from two to four suckers, and sometimes 



