152 



COLLEGE ZOOLOGY 



derived. There are well-developed muscular, nervous, digestive, 

 excretory, and reproductive systems; these are constructed in 

 such a way as to function without the coordination of a circu- 

 latory system, respiratory system, ccelom, and anus. 



Digestive System. — The 

 digestive system (Fig. 99) con- 

 sists of a mouth (tri), a pharynx 

 (ph) lying in a muscular sheath, 

 and an intestine of three main 

 trunks (i, i 2 , *») and a large 

 number of small lateral exten- 

 sions. The muscular pharynx 

 can be extended as a proboscis 

 (Fig. 97, j) ; this facilitates 

 the capture of food. Digestion 

 is both intercellular and intra- 

 cellular, i.e. part of the food is 

 digested in the intestinal trunks 

 by secretions from cells in their 

 walls; whereas other food par- 

 ticles are engulfed by pseudo- 

 podia thrust out by cells lining 

 the intestine, and are digested 

 inside of the cells in vacuoles. 

 The digested food is absorbed 

 by the walls of the intestinal 

 trunks, and, since branches 

 from these penetrate all parts 

 of the body, no circulatory 

 system is necessary to carry 

 nutriment from one place to 

 another. As in Hydra, no 

 anus is present, the faeces 

 being ejected through the 

 mouth. 



Fig. 99. — Anatomy of a flatworm. 

 en, brain ; e, eye ; g, ovary ; i u i 2> i 3 , 

 branches of intestine; hi, lateral nerve; 

 m, mouth ; od, oviduct ; ph, pharynx ; 

 /, testis; u, uterus; v, yolk glands; 

 vd, vas deferens; $ , penis; 5 , vagina; 

 $ 9 , common genital pore. (From 

 Lankester's Treatise, after v. Graff.) 



