PHYLUM PLATYHELMINTHES 



261 



behind, sometimes in front of, the middle of the length of the body. 

 In the most lowly organised group of Turbellaria (the Accela) the 

 intestine is represented merely by a vacuolated, nucleated mass of 

 protoplasm without, or with only an irregular, lumen. In the others 



FIG. 214. Ueneral plan of the 

 structure of a Rhabdocoele 

 Turbellarian. be. bursa 

 copulatrix ; en. brain ; e. 

 eye; g. germarium ; i. intest- 

 ine ; In. longitudinal nerve ; 

 m. mouth ; ph. pharynx ; 

 r.s. receptaculum ; s. unicel- 

 lular glands ; t. testis ; u. 

 uterus ; v. yitellarium : vs. 

 vesicula seminalis ; <J ejacu- 

 latory duct ; $ 9 common 

 genital aperture. (After Von 

 Graff.) 



01' 



Cft 



ov 



FIG. 215. Cteneral plan of the structure of a Polyclad. en. brain ; 

 i., st. intestine; In. longitudinal nerve cord; m. mouth; od. 

 oviduct; ov. ovary; ph. pharynx; phi. sheath of pharynx; i. 

 testes ; u. uterus ; vd. vas deferens ; vs. vesicula seminalis ; rf 

 male aperture; 9 female aperture. (After Von Graff.) 





it is sometimes a simple sac (Rhabdocoele Turbellaria Fig. 214, 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-Fluke, there is a pair of canals which 



