DIGESTIVE SYSTEM PROBOSCIS 



103 



The Digestive System. -The mouth is placed on the ventral 

 surface near the anterior end of the body (Figs. 53, 58, m). 

 It leads into a straight oesophagus (Fig. 53, oes), whence passes 

 off the intestine (int), which is continued as a straight 

 non- convoluted tube to the anus (a), situated terminally at 

 the posterior end of the body. The intestine is thrown out 

 throughout the greater part of its course into paired lateral 

 pouches. 



The alimentary canal is lined throughout by a ciliated 



,/ ^I7 i t iiiii'iiii'illim n 



Fig. 52. Diagrammatic transverse section of a Nemertine (Schizonemertea) through 

 the middle region of the body, b.m, Basement membrane ; cm, circular muscle 

 layer ; d.b, dorsal blood-vessel ; ep, epidermis ; g, generative organs ; int, intestine ; 

 lb, lateral blood-vessel ; l.m, longitudinal muscle layers ; n.c, lateral nerve-cord ; 

 n.l, nerve plexus ; p, proboscis ; p.s, proboscis sheath ; s.t, subcutaneous layer. 



epithelium. The oesophagus has, in addition to this layer, an 

 outer thick coat of large granular cells, which probably have a 

 glandular function. 



Proboscis. The most characteristic organ of the Nemertines is 

 the proboscis (Figs. 50, 53, 54). For many years its disposition 

 and function were misunderstood, and it was supposed to be a 

 portion of the digestive system. The proboscis, which lies dorsal 

 to the alimentary canal, opens at the extreme anterior end of 

 the body by a small pore (Figs. 51,53,58). When retracted it is 

 sometimes considerably folded, and lies in a long pouch or sheath. 

 To the walls of this sheath it is attached round its anterior 



