388 SYSTEMATIC ACCOUNT OF THE CESTODES. 



SYSTEMATIC ACCOUNT OF THE CESTODES. 



Rudolphi, "Entozoorum s. verm, intest. hist, nat.," 1808-1810. 



Fr. S. Leuckart, " Zoologische Bruchstiicke," Heft i., 1819. 



Dujardin, "Hist. nat. des Helminthes : " Paris, 1845. 



Van Beneden, " Vers Cestoides," Mtm. Acad. Sci. Bruxdles, t. xxv., 1851. 



It is not only in regard to the life-history and development of the 

 Cestodes that our knowledge has increased in scope and complete- 

 ness ; the same must be said of our knowledge of the different forms 

 and their natural relationships. 



Apart from the bladder-worms and certain more isolated species, 

 such as Liyula, the older naturalists knew only a single genus of 

 tape-worms, Tcenia. It was, therefore, an important step when 

 Rudolphi not only increased the number of the unsegmented tape- 

 worms by the erection of different genera (Caryophyllceus, Tricuspidaria), 

 but also separated a number of species from Tcenia on the ground of 

 the structure of the head (foveis dudbus instead of osculis quotum 

 suctoriis), and formed them into a special genus, Bothriocephalus. 

 Although Rudolphi himself, in his later writings, prepared the way 

 for the further breaking up of this family, by establishing a group of 

 Rhynchobothrii (i.e., TetrarhyncM grown into tape- worms), it remained 

 for long with its original content. This persisted, indeed, until van 

 Beneden made us acquainted with the manifold Cestode forms para- 

 sitic in rays and sharks, and was not only compelled by his ex- 

 tended knowledge to erect numerous new genera, but made, for the 

 first time, an attempt towards a natural division of the group, which 

 henceforth included also the bladder-worms. 



Van Beneden distinguished four families of tape-worms, distin- 

 guished according to the number and structure of their suckers : the 

 Tetraphylles, Diphylles, Pseudophylles ( = Bothriocephali sensu stricto), 

 and Aphylles (Teniens). It seems doubtful whether the group Diphyl- 

 lidia, which is only represented by a single genus, Echineibothrium 

 (Fig. 226, B), should be retained ; I should rather divide the Tetra- 

 phyllidia into Rhynchobothria and Phyllobothria, so that the Cestodes 

 would then fall into the four groups Rliyncliobothria (Tetrarhynchi 

 Phyllobothria, Tceniadce, and Bothriocephali (or Dibothria). 



The Rhynchobothria (Fig. 226, A) have a large head with four long 

 proboscides and four large suckers, which often coalesce in pairs. 



The Phyllobothria have four rarely two large, moveable, and 

 often very complex suckers, sometimes furnished with spines anteriorly, 

 and sometimes without armature. 



