VERMES 



1.35 



typical annelid are membranes, called dissepiments, which divide 

 the body-cavity into a series of compartments corresponding to 

 the external segments(Fig. 125). These membranes are pierced 

 by the alimentary canal, 



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which passes through the 

 entire length of the body, 

 from the mouth on the 

 ventral side of the first 

 segment to the anus in 

 the last. In many of the 

 segments there is a pair 

 of excretory tubules, the 

 nephridia, or segmental 

 organs, placed symmetri- 

 cally one on each side of 

 the alimentary canal, and 

 likewise a pair of germ- 

 elands. On the dorsal 

 side of the alimentary 

 canal is a longitudinal 

 blood vessel in which the 

 blood flows from the pos- 

 terior toward the anterior 

 end of the body, and on 

 the ventral side is a similar 

 vessel in which the blood 

 flows in the opposite direc- 

 tion ; these two vessels are 

 connected in each segment 

 by transverse branches, 

 the nervous system con- 

 sists of a brain, the cere- -ne.c0~ 



bral ganglia, situated in fig. 125. Nereis dumerilii. Semi-diagrammatic 



the first Segment On the view of the anterior portion oi the body with the 



_ dorsal body-wall in part removed and also a part 



dorsal side of the alimen- f the intestine at the posterior end. dot 1 



tary canal. From the dorsal vessel ; ^/, oesophageal glands ; i«A begin- 



7 _ nmg of intestine; ne.co, nerve cord; nepn, nepnn- 



brain two nerve cords dia ; as, oesophagus ; palp, palp ; para, parapoi 



pass off, one to the right ^'^ w ^i^ A ^^"^S- 



1 & p/i, pharynx, with its jaws; prcest, prostomium , 



and the -Other to the left, vent.vess, ventral vessel. (After Parker and Haswell.) 



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