VASCULAR SYSTEM OF NEREIS 



251 



movement of the jaws themselves and of the wall of the 

 apparatus is due to other muscles. 



The oesophagus is quite short ; into it opens a pair of saccu- 

 lated diverticula or glands. Then follows the intestine, which 



Fio. 127. Nereis, laid 

 oi>en by removal of 

 the dorsal body- wall. 

 br, Cerebral ganglion, 

 from which three pairs 

 of nerves are repre- 

 sented as arising ; a 

 pair to the tentacles, 

 a pair to the palps, 

 and a pair (con) pass- 

 ing one on eacli side 

 of the buccal region, to 

 join the ventral nerve- 

 cord; mo, mouth, ex- 

 posed byremoval of the 

 dorsal wall of the buc- 

 cal region (Buc) ; pgn, 

 the paraguaths in its 

 wall ; 1'h pharynx ; 

 J, the large "jaws" 

 embedded in its wall ; 

 J.mus, the muscles 

 which work the jaws ; 

 s/t, the muscular 

 sheath ; diaph, the 

 " diaphragm " ; oes, 

 oesophagus ; gl, its 

 glands ; st, stomach ; 

 int, intestine ; Sept, 

 septum ; d.v, dorsal 

 blood trunk ; p.r, 

 perivisceral branches, 

 one pair in each seg- 

 ment ; P, palp ; t, ten- 

 tacle ; per, peristo- 

 mium ; per.ci, two of 

 the four peristomial 

 cirri ; ppIII, the first 

 parapodium which be- 

 longs to the third true, 

 but second apparent, 

 segment ; cir.m, circu- 

 lar muscular coat ; 

 Ig.m, longitudinal mus- 

 cular coat of the body- 

 wall. 



extends through the rest of the body as a thin-walled tube, 

 slightly dilated at the insertion of the septa. 



The vascular system consists of a contractile dorsal vessel and 

 of a non-contractile ventral vessel extending along the whole length 

 of the body, from each of which paired and sejrmentally-arranged 



