352 NEREIS CHAP. 



there is, in addition to the ordinary setae, a stouter, straight, 

 dark-coloured seta (ac\ the pointed apex of which projects 

 only a short distance on the surface ; this is termed the 

 aciculum. The ordinary setae are exceedingly fine but 

 stiffish, chitinous rods, of which two principal kinds are 

 recognisable ; both have a terminal blade articulating with 

 the main shaft of the seta by a distinct joint. On the 

 dorsal side of the parapod is a short, cylindrical, tentacle- 

 like appendage, the dorsal cirrus (Fig. 88, dors, cirr), and 



dors, cirr 



noio 

 neuro 



^S&fe, 



vent.cirr 



FIG. 88. Nereis dumerilii. A single parapod magnified, ac. aciculum ; dors, cirr, 

 dorsal cirrus ; neuro, neuropod ; noto, notopod ; vent, cirr, ventral cirrus. 

 (From Parker and Haswell's Zoology, after Claparede.) 



a similar, somewhat shorter, appendage, the ventral cirrus 

 (vent, cirr}, is situated on its ventral side. The last 

 segment of the body, the anal segment, bears posteriorly a 

 small rounded aperture, the anus -, this segment is devoid 

 of parapodia, but bears a pair of appendages, the anal cirri, 

 similar in character to the cirri of the ordinary segments, 

 but considerably longer. 



On the ventral surface near the bases of the parapods, 

 there is in each segment a pair of very fine nephridiopores 

 (p. 341), through which the sperms probably pass to the 

 exterior, there being no special genital apertures. Dorsal 

 pores are also wanting. 



