THE CESTOIDEA 



109 



The posterior contractile bladder naturally persists only in those 

 genera which do not drop their proglottids, e.g. Ichthyotaenia, and 

 various Taenia, spp., which inhabit Teleostei ; in other cases, after 

 the separation of this terminal proglottid, the four collecting canals 



a 



FIG. VII. Plans of excretory system (after Pintner). 



l.Acanthobothrium coronatum, Rud. Young. The two canals on each side pass into one 

 another in the scolex, but are not connected right and left. Posteriorly all four open into the 

 contractile bladder (e). 



2. PhyUobnthrium gracile, Wedl. Scolex. The two canals of either side pass into the 

 phyllidia of this side ; i is an " island " formed by the local splitting of a canal and the reunion 

 at once of the two branches. 



3. Tetrarhynehus. Scolex. The frontal, transverse vessel (a) unites the right and left 

 canals at the point of recurrence. 



4. Scolex of Cysticerciis arionis (i.e. of Taenia multiformis). b, rostellum, which causes the 

 vessel (a) to form a circular loop, into which the four canals fall. 



5. Taenia. Scolex. The muscular sucker also causes the formation of a loop in each 

 of the longitudinal canals, a, the circular vessel ; b, position of the rostellum j c, the four 

 acetabular loops or islands. 



6. Tetrarhynchus and Tetracotylea. Proglottids. The ventral canal becomes'wicler than 

 dorsal, and there is a transverse canal (/) in each proglottid. 



came to open independently ; or, in some cases, a median duct 

 develops from the last transverse connecting canal. But in a con- 

 siderable number of instances the main canals effect new lateral 

 communications in the scolex, neck, and proglottids; these "foramina 

 secundaria " appear in Schistocephalus to be segmentally repeated. 



