SECT, ix PHYLUM ANNULATA 189 



constitute one of the distinguishing features of the class 

 Chaetopoda or " bristle-footed " worms of the phylum 

 Annulata. Of these a good and common example is Nereis 

 a marine Annelid of common occurrence under stones 

 and among shells and seaweed on the 

 sea- shore in all parts of the world. The 

 following account of the European Nereis 

 dumerilii will apply, with slight differences, 

 to our common Nereis virens. 



In shape (Figs. 106-109) the body, 

 which may be about 7 or 8 centimetres 

 in length, is long and narrow, approxi- 

 mately cylindrical, somewhat narrower 

 towards the posterior end. A very distinct 

 head, bearing eyes and tentacles, is recog- 

 nisable at the anterior end; the rest is 

 divided by a series of ring-like narrow 

 grooves into a corresponding series of seg- 

 ments or metameres, which are about eighty 

 in number altogether ; and each of these 

 bears laterally a pair of movable muscular 

 processes called the parapodia, provided 

 with bundles of bristles or seta. The head 

 (Fig. 109) consists of two parts, the pro- 

 stomium (prcest) and the peristomium 

 (peris t). The former bears on its dorsal 

 surface four large rounded eyes, in front FIG. 106.- Nereis du- 

 a pair of short cylindrical tentacles (tent), 

 and further back a pair of somewhat 

 longer stout appendages or palpi (palp}. The peristo- 

 mium, which presents some resemblance to the segments of 

 the body, though wanting the parapodia. bears laterally four 

 pairs of long slender cylindrical tentacles (perist, tent} : 



