406 The Animal Kingdom 



The cavity of the protrusible pharynx leads into the intestine. The 

 intestine has three principal branches, two posterior and one anterior. 

 All portions are lined with columnar epithelium. From the main 

 branches lead many smaller lateral sub-branches which permit the food 

 to pass into all regions. The digested food passes from cell to cell by 

 diffusion, and undigested materials are ejected through the opening of 

 the pharynx by reverse peristaltic movements. 



The tubes of the excretory system ramify throughout the entire 

 body. There are many flame cells (Fig. 134,5) in all regions. 



. PHARYNGEAL 

 CHAMBER 



BASEMENT MEMBRANE 

 CIRCULAR MUSCLES. 

 PHARYNGEAL CAVITY 

 LONGITUDINAL MUSCLES. 



CIRCULAR MUSCLES 



LUMEN OF PHARYNX 

 INNER EPITHELIUM 



GLANDULAR LAYER 



OUTER EPITHELIUM. 

 CILIA 



.EPIDERMIS 



.LONGITUDINAL 

 MUSCLES 



PARENCHYMA 



IRCULAR 

 MUSCLES 



NTESTINE 



NERVE CORD 



Fig. 134. — The planarian worm, Dugesia sp. A, Dorsal view of entire worm; B, 

 flame cell; C, cross section through the region of the pharynx. 



The nervous system consists of two anterior thickenings of nerve 

 tissue and associated nerves. From these thickenings, short nerves pass 

 anteriorly into the eyes, and two longitudinal nerve cords pass posteriorly 

 along either side. Many transverse connections between these two 

 nerve cords give a ladderlike appearance to the system. Small peripheral 

 nerves originate on the longitudinal nerves and go to the muscles and 

 epidermis. 



