PHARYNX 



353 



The mouth leads into a wide buccal cavity, which is 

 continued back into a pharynx. In the pharynx are a 

 number of very small, dark brown, chitinous denticles, which 

 are very regularly arranged. The posterior part of the 

 pharnyx has very thick walls composed of bundles of 

 muscular fibres which are concerned in the movements of 

 a pair of laterally placed chitinous jaws. The anterior 

 part of the alimentary canal is capable of being everted, as 



sp 



FIG. 89. Trochosphere of the worm Enf>omatus, from the side. an. anus ; md. 

 mid-gut ; n. larval head-nephridium ; sp. neural plate (brain) ; st. stomodaeum ; 

 tvk. preoral ciliated ring ; wk\. post -oral ciliated ring. (From Lang's Compara- 

 tive Anatomy, after Hatschek.) 



a proboscis, until the jaws are thrust forth and project freely, 

 so that they can be brought to bear on some small living 

 animal or fragment of animal matter, which is thus seized 

 and swallowed. 



In correspondence with its different mode of life, Nereis 

 is much better provided with sense-organs than is the 

 earthworm. The tentacles and palps, as well as the cirri, 

 are probably organs of touch ; and, as we have already seen, 



PRACT. ZOOL. A A 



