VESMES— INTESTINAL CANAL 



207 



It has an accessory intestine lying close to it which passes anteriorly 

 and posteriorly into longitudinal ciliated channels in the main intestine, 



Pig, 137.— Enteric canal, vascular system, and nepbridia of Echiurus. sg, Lateral vessels of 

 the prostomium ; re?, dorsal vessel of the prostommm : vdi, dorsal vessel of the fore-gut (yda) ; k, 

 crop ; md, raid-gut, with the accessory intestine (nd) ; vv^ ventral vessel ; n, nephridia ; t, their 

 funnel ; as^ anal glands ; ed, hind -gut ; a, anus ; 7)i&, muscles of the anterior hooked setee ; in, mouth. 



and is justly considered as the connecting piece of these channels 

 arched over and thus separated from the intestine. 



The mid-gut of the Myzostomidce (Fig. 175, p. 262), with its 

 branched diverticula which stretch as far as the lateral edge of the 

 body, recalls the mid-gut of the Annelid species Sphincter, whose body 

 is also broad and disc-like. 



While among the Sipuncidacea the mid-gut in the Priapulidce runs 

 in a straight line through the body, in the SipuncuUdce (Fig. 138) it 

 forms a descending limb which runs through the trunk to the posterior 



