PHYLUM PLATY1IELMINTHES 



163 



4. Class III. Cestoda 



a. The Tapeworm — Tcenia 



The tapeworm, Tcenia solium, is a common parasite which 

 lives as an adult in the alimentary canal of man. A nearly 

 related species, T. saginata, is also a parasite of man. Tcenia, 

 as shown in Figure 107, is a long 

 flatworm consisting of a knob-like 

 head, the scolex (Fig. 107, B), and a 

 great number of similar parts, the 

 proglottides, arranged in a linear 

 series. The animal clings to the 

 wall of the alimentary canal by 

 means of hooks (Fig. 107, B, 2) and 

 suckers (j) on the scolex. Behind 

 the scolex is a short neck (4) followed 

 by a string of proglottides which 

 gradually increase in size from the 

 anterior to the posterior end. The 

 worm may reach a length of ten feet 

 and contain eight or nine hundred 

 proglottides. Since the 

 proglottides are budded 

 off from the neck (Fig. 

 107, B, 4), those at the 

 posterior end are the 

 oldest. The production 

 of proglottides may be 



compared to the forma- Fig. 107. - The tapeworm. A, Tenia 



tion of ephyra? by the sa S^ nata - The approximate lengths of the 

 . portions omitted in the drawing are given 



hydra-tuba of Aurelia At 



(Fig. 81), and is called 

 strobilization. 



The anatomy of the 

 tapeworm is adapted to 



the branched uterus and longitudinal 

 and transverse excretory vessels are shown. 

 B, head or scoiexof Tania solium, i, rostellum; 

 2, hooks; 3, suckers; 4, neck; j, commence- 

 ment of strobilization. (A, from the Cam- 

 bridge Natural History; B, from Shipley and 

 MacBride.) 



