ANNUL AT A, 



179 



CHAPTER XVI. 

 ANNUL AT A. 



POLYGORDIUS. ARENICOLA. HIRUDO. LUMBRICUS. 



I.— POLYGORDIUS. 



Phylum - 

 Sub-Phylum 



Class 



Annulata (p. 237). 

 Annelida (p. 238). 

 Archianneliua (p. 239). 



Polygordhis neapolitanus is a small 

 delicate marine (1^2 inch) worm, of elon- 

 gated body, found in the sand at moderate 

 depths. It is of a pale pink hue. At the 

 anterior end are a pair of small tentacles, 

 the prostomial tentacles, covered with fine 

 setse. They are parts of the prostomuwi^ 

 a lobular process lying anterior and dorsal 

 to the mouth. Immediately behind the 

 mouth is the peristondum, a large and 

 well-defined segment. The rest of the 

 body is divided externally and internally 

 into a series of segments. The terminal 

 or anal segment is swollen and bears the 

 anus. On its broadest part this segment 

 bears a ring of papillae. The mouth leads 

 into an oesophagus which continues as a 

 simple intestine terminating in the anus. 

 The ectoderm is a simple epithelium with 

 unicellular glands ; it secretes a thin cuticle. 

 Below it the mesoderm forms a well- 

 developed system of longitudinal muscles. 

 Inside them is the delicate coelomic 

 epithelium, lining a spacious coelom. This 

 is divided by dorsal and ventral mesen- 

 teries, in which are simple blood-vessels, 

 and by transverse septa between each 

 segment. Each segmental part of the 

 coelom opens by simple paired tubes (or 

 nephridia) to the exterior. The nervous 

 system is still part of the ectoderm. It 

 consists of a brain in the prostomium. 



Fig. 105 — POLYGORDIUS 



Neapolitan us. 



Prostomial Tentacles. 



Anus. 

 Entire animal seen from dor- 

 sal aspect X 5. (After 

 Fraipont.) 



