PHYSIOLOGY OF THE INVERTEBRATA. 



65 



In the Ehdbdopleura the tentacula are narrower, 

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

 somewhat resemble the BracMopoda. " The mouth;. i& 

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

 side to the anus." 



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

 mouth (Fig. 1 7) is situated 

 on the lophophore, and 

 is surrounded by a num- 

 ber of ciliated tentacula. 

 The mouth leads into an 

 oesophagus which passes 

 iuto 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 



Fig. 17.— Alimentary Canal of 

 polyzoon. 



a = tentacles, i = lophophore. c = mouth. 

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

 mach, g = intestine. A = anus. 

 i = nervous ganglion. 



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 



