192 MANUAL OF ZOOLOGY SECT, ix 



ccelomic fluid. The space is divided by a series of transverse 

 partitions or septa passing inwards from the body-wall to the 

 wall of the alimentary canal opposite the grooves between 

 the segments, and thus dividing the ccelome into a series of 

 chambers, each of which corresponds to one of the 

 segments. These partitions are not complete, spaces being 

 left through which neighbouring chambers communicate. 



The mouth leads into a wide cavity, the buccal cavity, 

 continued back into a pharynx (Fig. 103, ph.). In the 

 pharynx are a number of very small dark brown chitinous 

 denticles, which are very regularly arranged. The posterior 

 part of the pharynx has very thick walls composed of 

 bundles of muscular fibres, which are concerned in the 

 movements of a pair of laterally placed chitinous jaws. 



Behind the pharynx the alimentary canal narrows 

 considerably to form a tube, the oesophagus (ces.\ which 

 runs through about five segments to open into the intestine. 



The anterior part of the alimentary canal is capable 

 of being everted, as a proboscis, until the jaws are thrust forth 

 and thus rendered capable of being brought to bear on 

 some small living animal or fragment of animal matter, to 

 be seized and swallowed as food. 



Into the oesophagus open a pair of large unbranched 

 glandular pouches, or cceca (gl.\ which probably are of the 

 nature of digestive glands. The intestine (int.) is a straight 

 tube of nearly uniform character throughout, regularly 

 constricted between the segments. 



Nereis has a well-developed system of vessels filled with 

 blood of a bright red colour. A main dorsal vessel (Figs. 

 103 and 104, dors, ves.) runs from one end of the body to the 

 other above the alimentary canal, and is visible in places 

 through the body-wall in the living animal. It, as well as 

 the majority of the vessels, undergoes contractions which 



