V 



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266 



ZOOLOGY 



table organisms, or floating organic debris, by their own active 

 efforts. Others the Digenetic Trematodes and the Cestodes 

 having reached a favourable situation in the interior of their host, 

 remain relatively or completely passive. An alimentary canal is 



crt 



FIG. 211. General plan of the 

 structure of a Rhabdococle 

 Turbellarian. b. c. bursa 

 copulatrix ; en. brain ; e. eye ; 

 g. geriuarium ; i. intestine ; 

 In. longitudinal nerve ; m. 

 mouth ; ph. pharynx ; r.s. 

 receptaculum sefninis ; s. uni- 

 cellular glands ; t. testis ; u. 

 uterus ; v. vitellariura ; vs. 

 vesicula seminalis ; <J ejacu- 

 latcry duct ; <J 9 common 

 genital aperture. (After Von 

 Graff.) 



- OV 



FIG. 212. General plan of the structure of a Polyclad. en. brian ; 

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

 ov. ovary ; ph. pharynx ; phi. sheath of pharynx ; t. testes ; u. 

 uterus .vd. vas deferens ; vs. vesicula seminalis ; c$ male 

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



completely absent in the last-named group, nutrition being effected 

 by the absorption of digested matter from the interior of the 

 animal in which the Cestode lives. In all the rest of the Platy- 

 helminthes there is an alimentary canal, which never opens on the 



