i8o 



ANNULATA. 



Fig. io6.— Transverse Section of Polygokdius, Semi- 

 Diagrammatic. (After Fraipont.) 



Dorsal Blood-vessel. 



Coelom. 



Intestine. 



Oblique Septum 



bearing the 



Gonad. 



Nerve-cord. 



Ventral Blood-vessel. 



a ring round the oesophagus and a ventral nerve-cord, swollen into 

 ganglia in each segment. Immediately behind the prostomium and 

 placed laterally are a pair of ciliated pits which are probably sensory. 



Fig. 107. — Coronal Longitudinal Section of 

 PoLYGORDlus (Highly Magnified). 

 Intestine. 



Segment. 



Segment. 



B^Coelom. 



^Circular Blood- 

 vessel. 



Nephridium. 

 Nephridiopore. 



The sexes are separate and the testes and ovaries arise on two diagonal 

 muscular bands intersecting the coelom. 



