2m 



ZOOLOOY 



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

 etforts. Others — the Digenetic Treinatodes and the Cestodes — 

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

 remain relatively or completely passive. An alimentary canal is 



Fig. 211.— General plan of tlie 

 structure of a Rhabdocoele 

 Turbellarian. b. c. bursa 

 copulatrix ; en. brain ; e. eye ; 

 f/. germariuni ; i. intestine ; 

 In. longitudinal nerve ; m. 

 nioutb ; ph. pharynx ; r.s. 

 reeeptaculum seminis ; s. uni- 

 eellular glands; /.testis; u. 

 uterus ; v. vitellarimn ; vs. 

 vesicula seminalis ; (J ejacu- 

 latcry duct ; S 9 common 

 genital apei-ture. (After Vou 

 Graff.) 



Fig. •212. — General plan of the structure of a Folyclad. en. brian ; 

 c. eye ; i., st. intestine ; In. longitudinal nerve cord ; ni. mouth ; 

 ov. ovary ; ph. pharynx ; j5/ii. sheath of pharynx ; (. testes ; v. 

 uterus vd. vas deferens ; ■us. vesicula seminalis ; S ^^^^ 

 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 



