ARENICOLA. 



185 



hold the front part of the alimentary canal in position. 

 There is no dorsal nor ventral mesentery, but in the " tail " 

 region, from segment 20 backwards, there are regular trans- 

 verse septa. Hence the alimentary canal, from segment 4 

 to segment 19 inclusive, is free to move in the coelom. 



The pharynx leads into a long (Esophagus which widens 



out into the stoinach. Just before the commencement of 



Aiim t ^^ latter there is a pair of oesophageal glands 



or pockets, the lumen of which opens into the 



oesophagus. They are probably digestive glands. The 



Fig. 112. — Transverse Section of Arenicola (Diagrammatic). 



Dorsal Blood-vessel receiving Efferent Branchial. 



erent 

 Branchial. - 



erent 

 Branchial. 



Oblique 



Longitudi 

 Muscle 



Circular Muse 

 ^ ^ ^ with Ectode 



Ventral Vessel. '" ^"^"'-^ and_ Cuti 



outside. 

 Nerve Cord. 



the left is seen the arrangement of the first six branchial segments ; on the right the last se 



Stomach is wide, and is covered with yellow-cells^ intersected 

 by a network or plexus of blood-vessels. At about the level 

 of the seventh pair of gills the stomach passes into the 

 intestine which terminates in an anus. 



Arenicola is perpetually employed in passing quantities 

 of sand and food-particles through its alimentary canal, 

 digesting the latter and egesting the former. 



