326 PLATYHELMINTHES. 



Order 3. CESTODA.* 



Elongated and usually segmented Platyhelminthes -without mouth 

 or alimentary canal, with organs for attachment at the anterior 

 extremity. 



The tape-worms, which may easily be recognised by their band- 

 shaped usually segmented bodies, are parasitic in the alimentary 

 canal of Vertebrata, and were formerly taken for single animals. 

 Steenstrupp was the first to introduce a different view, according 

 to which the tape-worm is a colonial animal, a chain of single 

 animals, each segment or proglottis being an individual. There are, 

 however, Gestoda, like Caryophyttceus, which are destitute both 

 of external segmentation and of segmentation of the gene- 

 rative organs : while in other cases the segments of the body 

 are clearly differentiated, and each is provided with a set of genera- 

 tive organs, but they do not attain individual independence. The 

 proglottides, however, usually become separated oft', and in some 

 cases (Echineibothrium) after their separation from the body of the 

 tape-worm continue to live for a long time independently, and even 

 increase considerably in size ; so that although the individuality 

 of the tape-worm may be justly insisted on, yet the subordinate 

 and morphologically more restricted degree of individuality of the 

 proglottis must also be admitted. This is the only satisfactory 

 mode of regarding the Cestoda ; especially as the entire tape-worm, 

 and not the proglottis alone, corresponds to the Trematode, and is 

 to be derived from the latter by a simplification of organization and 

 loss of the alimentary canal. 



The anterior part of the tape-worm is narrow, and presents a 

 terminal swelling by which it attaches itself. This anterior swollen 

 part is distinguished as the head of the tape-worm, but it is only 

 its external form which entitles it to this name. In Caryophyllceus 



* Besides the older works and papers of Pallas, Zeder, Brernser. Rudolphi, 

 Diesing, and others, compare van Beneden, ' Les vers cestoi'des on acotyles," 

 Brussels, 1850. Kuchemueister, " Ueber Cestoden im Allgemeineu uiul die 

 des Menschen insbesondere," Dresden, 1853. V. Siebold. " Ueber die 

 Band- und Blasen-wiirnier," Leipzig. 1854. G. Wagoner, " Die Entwicke- 

 lung, der Cestoden," Nov. Act. Leojt.-t'tir., Tom XXIV., Suppl., 1854. 

 G. Wagener, " Beitrag zur Entwickelungsgeschichte der Eingeweidewiiimer," 

 Haarlem. 1857. R. Leuekart, " Die Blasenbandwiinner und ihre Entwicke- 

 lung," Giessen, 185(1. R. Leuekart, ''Die menschlicbeii Parasiteu," Bd. I.. 

 Leipzig, 1862. F. Sommer and L. Landois, '' Ueber den Bau der geschlechts- 

 rcifeu Glieder von Bothriocephalus latus." Zritxelir. f. ir-isx. Zool., 1872. 

 F. Sonmier, ' Ueber den Bau und die Entwickelungsgeschichte der Geschlechts- 

 organe von Taenia mediocanellata und Taenia solium," Ibid., Tom XXIV., 1874. 



