

CHAPTER III 



CESTODA 



INTRODUCTION NATURE OF CESTODES OCCURRENCE OF CESTODES 



THE TAPE- WORMS OF MAN AND DOMESTIC ANIMALS TABLE 



OF THE LIFE -HISTORIES OF THE PRINCIPAL CESTODES OF MAN 



AND DOMESTIC ANIMALS STRUCTURE AND DEVELOPMENT OF 



CESTODES TABLE FOR THE DISCRIMINATION OF THE MORE 



USUAL CESTODES OF MAN AND DOMESTIC ANIMALS CLASSI- 

 FICATION. 



THE Cestodes or Tape - worms are exclusively endoparasitic 

 Platyhelminthes living, in the adult condition, in the alimentary 

 canal of Vertebrates, with the exception of Archigetes (Fig. 37), 

 which may become mature in the body-cavity of Tulifex. In 

 relation with this wholly parasitic existence, the Cestodes exhibit 

 certain characteristic modifications in structure and mode of 

 development, such as the formation, by the segmentation of the 

 " neck," of a (usually) long chain of " proglottides " or joints, which 

 form the " body " of the Cestode ; and the entire absence of an 

 alimentary tract, both in the larva and adult. As an adaptation 

 to the fixed mode of life, the anterior end (head, scolex) is modi- 

 fied to form an adhering organ. Various adaptive forms of larvae 

 are known. These live in the internal organs of one or more 

 intermediate hosts, and are transferred to the final host passively 

 during a meal. Lastly, there is the curious metamorphosis by 

 which the adult is formed from a portion (scolex) of the larva. 1 



Taenia solium, from man (Fig. 39, B), or a Calliobothrium 

 (Fig. 36), from an Elasmobranch fish, is fixed to the mucous lin- 

 ing of the intestine of its host by means of a radially -constructed 

 1 Cf. p. 5. 



