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 



en 



vs 



. 214. General plan of the 

 ucture of a Rhabdocoele 

 bellarian. be. bursa 



pulatrix ; cn. brain ; e. 

 ye; g. germarium ; i. intest- 

 ae ; In. longitudinal nerve ; 

 i. mouth : ph. pharynx ; 

 .8. receptaculum ; s. unicel- 

 Jlar glands ; t. testis ; u. 

 terus ; v. vitellarium : vs. 

 esicula seminalis ; S ejacu- 

 itory duct; rf 9 common 

 enital aperture. (After Von 

 Jraff.) 



cn 



ov 



FIG. 215. General plan of the structure of a Folyclad. cn. brain ; 

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

 oviduct; ov. ovary; ph. pharynx; ph l . sheath of pharynx; t. 

 testes ; u. uterus ; vd. vas def erens ; vs. vesicula seminalis ; 6 

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



it is sometimes a simple sac (Rhabdoccele 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 



