PHYLUM PLATYHELMINTHES 



251 



sac (Rhabdoccele Turbellaria (Fig. 200), a few Trematoda), with or 

 without short lateral diverticula. In the majority of the Trematodes 

 it consists of a pair of simple canals ; but in some, as in the Liver- 



or 



en 



FIG. 200. General plan of the 

 structure of a Rhabdocoele 

 Turbellarian. l>. e. bursa 

 copulatrix ; ci>. brain ; e. eye ; 

 g. germarium ; i. intestine ; 

 In. longitudinal nerve ; . 

 mouth ; ph. pharynx ; rs. 

 receptaculuni seminis ; n. uni- 

 cellular glands : t. testis ; u. 

 uterus; vs. vesicula semin- 

 alis ; <J ejaculatory duet ; 

 S common genital aper- 

 ture. (After Von Graff.) 



OV 



Fi'.. 201. General plan of the structure nf a Polyclad. en. brain ; 

 e. eye; (.intestine; l,>. longitudinal nerve cord; i. mouth; or. 

 ovary; j>!i. phaiynx ; jih^. sheath of pharynx; t. testes ; u. 

 uterus ; cr/. vas deferens ; rs. vesicula seminalls ; <J male 

 aperture ; ? female aperture. (After Von Graff.) 



fluke, there is a pair of canals which give off numerous branches. 

 In the Polycladida (Fig. 201) there is a central cavity from which 

 numerous branching canals are given off. In the Tricladida (Fig. 

 202) one median canal passes forwards from the pharynx, 



