ZOOLOGY 



SECT. 



is very different from that of such an average Trematode as the 

 Liver-fluke. The body of an ordinary Cestode is of great length, 

 sometimes extending even to a good many feet, and relatively narrow, 

 being compressed into the form of a ribbon. The anterior end 

 is attached to the host by means of suckers and hooks placed on 

 a rounded lobe, the head or scolex, connected with the body by a 

 narrow part or neck. The head is usually rather radially than 



rb 



FIG. 19-2. Tetrarhynchus. 



FIG. 193. Tsenia echinococcus. 



(After Cobbold.) 



bilaterally symmetrical, witWourjsjiekers and a circlet of hooks. 

 The hooks, when present, are borne on a longer or shorter retractile 

 process, the rostellwm, the long axis of which is in line with the 

 long axis of the body. In Tetrarhynchus (Fig. 192) there are four 

 very long and narrow rostella covered with booklets. 



The Cestoda are devoid^^ofjuouth, and in most of them the 

 genital apertures are marginally placed, so that, externally, there 

 is, except in the case of a few in which the genital apertures are 

 not marginal, nothing to distinguish the dorsal . surface from the 

 ventral. The body, or strobila, which is narrower in front than it 

 becomes further back, is made up throughout its length of a series 

 of segments, or proglottides, which become larger and more dis- 

 tinctly marked off from one another as we pass backwards. Tcenia 



