POLYCHAETA 



273 



pharynx, however, is not well developed, the oesophagus is a thin- 

 walled tube with no such development as the gizzard of the earthworm 



"'^'^^ T /?>'•• 



not.~^ 



in.r.{ 



Fig. 189. Arenicola marina. Side view. After Ashworth. ac/i. ist achaetous 

 segment; a.r. anterior region; m.r. median region; not. notopodium; neur. 

 neuropodium; pr. prostomium; p.r. posterior region; per. peristomium; 

 phar. pharynx. 



and it bears only a single pair of coeca. The intestine is the longest 

 part of the gut, the seat of digestion and absorption, and it is invested 

 by a layer of yellow cells. The blood system, which also contains 



