ANNELIDA : THE EARTHWORM, NEREIS 219 



consisting of unstriped fibres running around the body, and 



below this again lies a much thicker longitudinal layer of 



muscle, composed of similar 



fibres running along the 



body and placed in rows 



which stand at right angles 



to the surface, supported by 



connective tissue. Within 



the longitudinal muscle is 



the ccelomic epithelium, 



which is here a layer of 



pavement cells lining the 



body cavity. 



The alimentary canal is 

 Out. straight. It be- 



gins with a 

 short, wide, thin -walled 

 mouth or buccal cavity in 

 the first three segments, 

 which leads into a structure 

 with thick muscular walls 

 known as the pharynx. 

 This lies in front of the 

 septum between the fifth 



Fig. 137. — A diagram of a longi- 

 tudinal section of an earth- 



a.v.s. Anterior vesicula seminalis. 

 a.v.s 1 . Posterior lateral horn of the 

 same overhanging the 

 oesophagus. 

 cr. Crop. 

 giz. Gizzard. 

 int. Intestine. 

 ;«. Mouth. 

 ces. (Esophagus. 

 p.v.s. Posterior vesicula seminalis. 

 p.v.s' . Horn of the same overhang- 

 ing the oesophagus. 

 per. Peristomium. 

 ph. Pharynx. 

 pr. Prostomium. 

 sup.ph.g-. Suprapharyngeal ganglion. 

 ty. Typhlosole. 

 v.n.c. Ventral nerve cord. 

 1-23. Segments. 



The blood vessels are omitted. 



15 



