X 



PHYLUM ANNULATA 



407 



to the wall of the buccal cavity and pharynx are a number of 

 bands or sheets of muscle, 

 the protractor muscles, by 

 the contraction of which 

 this anterior part of the 

 alimentary canal is capable 

 of being everted as a 

 /n'oboscis until the jaws are 

 thrust forth and thus ren- 

 dered capable of being 

 brought to bear on some 

 small living animal, or 

 fragment of animal matter, 

 to be seized and swallowed 

 as food. The proboscis is 

 withdrawn again by a 

 retractor sheet of muscle, 

 which passes inwards and 

 forwards to be inserted 

 into the wall of the ali- 

 mentary canal at the junc- 

 tion of the pharynx and 

 oesophagus. 



Into the oesophagus open 

 a pair of large unbranched 

 glandular pouches, or cceca 

 (#/.), which probably are 

 of the nature of digestive 

 glands. The intestine (int.) 

 is a straight tube of nearly 

 uniform character through- 

 out, regularly constricted 

 between the segments 

 the constrictions becoming 

 much deeper towards the 

 posterior end of the body. 

 The part of the intestine 

 which lies in the last 

 segment is termed the 

 rectum. 



The wall of the ali- 

 mentary canal (Fig. 322) 

 consists (1) of the visceral 

 layer of the peritoneum 

 (vise, peri.) ; (2) of a layer of 

 longitudinal muscular fibres (long, mus.) : (3) of a layer of circular 

 muscular fibres (circ. mus.); (4) of the enteric epithelium (ent. ep.\ 



FIG. 321. Nereis dumerilii. Semi-diagrammatic 

 view of the anterior portion of the body, with the 

 dorsal body-wall removed, so as to show the ali- 

 mentary canal, the septa, the blood-vessels and the 

 iiephridia ; a portion of the intestine removed so as 

 to show the ventral blood-vessel and nerve-cord 

 which lie below : dors. ves. dorsal vessel ; gl. oeso- 



'phageal glands; int. beginning of intestine; ne. co. 



I nerve cord ; neph. nephridia ; <>'. oesophagus ; palp. 



' palp ; para.-parapodia ; perist. peristome ; perist. tent. 

 peristomial tentacles ; ph. pharynx with its jaws ; 



fpntst. prostoinium ; << n.t. res. ventral vessel. 



