PHYSIOLOGY OF THE INVERTEBRATA. 



65 



shaped. In the Rliabdopleura the tentacula are narrower, 

 but longer, than any other Polyzoa ; in this respect they 

 somewhat resemble the Brachiopoda. "The mouth is 

 situated beneath the free margin of the disc, on the opposite 

 side to the anus." 



(2) The Fhyladolmnata are all fresh-water Polyzoa. The 

 mouth (Fig. 17) is situated 

 on the lophophore, and 

 is surrounded by a num- 

 ber of ciliated tentacula. 

 The mouth leads into an 

 a^sophagus which passes 

 into a muscular pharynx. 

 "The particles of food 

 are carried down the 

 inner surface of each ten- 

 tacle, and the mouth and 

 pharynx expand to re- 

 ceive such as are appro- 

 priate, as if by an act of 

 selection. The rejected 

 particles pass out between 

 the bases of the tentacula, 

 or are driven off by 

 the centrifugal currents." 

 The muscular pharynx 

 leads into a capacious 

 stomach. The narrow 

 intestine is continued 

 from the posterior end of 



the stomach, and terminates in an anus situated near the 

 mouth. The intestine is bent backwards, so that it runs 

 almost parallel with the anterior portion of the alimentary 

 canal. The walls of the stomach are studded with cells or 

 follicles of a pancreatic nature ; and its orifice is surrounded 

 by cilia. The food particles are constantly regurgitated into 



E 



Fig. 17. — Alimentary Canal of 

 polyzoon. 



a = tentacles. /■ = lophophore. c = month. 

 d = oesophagus, c = pharynx, f = sto- 

 mach, g = intestine. h = anus. 

 k — nervous ganglion. 



