PHYLUM PLATYHELMINTHES 



267 



or cysticercoid of the Cestode. The most important difference 

 between these is in the presence in the former of an enteric cavity, 

 and its absence in the latter. There seems to be something to be 

 said in favour of the view that the enteric cavity of the cercaria is 

 represented by the frontal sucker of some scolices, and by the 

 rostellum of the majority. 



*j ' 



Between the adult Cestodes and the Trematodes an intimate 

 relationship is traceable. Garyophyllceus (Fig. 195) is a Cestode 

 which, but for the absence of an enteric cavity and the want 



NemerMnea 



Pol, 



cladida. 



MonogeneUca 



Rhabdoeoelida 

 Cfenophora 



Lower Coelenter&tes 



FIG. -213. Diagram of the relationships of the Platyhelminthes (together with the Nemertinea). 



of organs of adhesion at the posterior end, is not far distant 

 from the Trematodes ; and the same might be said of Ampliip- 

 tychcs (Fig. 196), Amphilina, and Arcliigetes (Fig. 197). The most 

 important differences between a Cestode and a Trematode, in 

 addition to the absence of an enteric cavity in the former and 

 its presence in the latter, is the occurrence in the Cestodes of stro- 

 bilation. Ligula in a certain sense forms a connecting link in this 

 respect between the Trematode and the ordinary Cestode, the 

 body being elongated, and the reproductive organs repeated as 

 in the normal Tape- Worm, but without the corresponding division 

 of the body into a string of definitely separated proglottides. 



