352 



NEREIS 



CHAP. 



the pointed apex of which projects only a short dis- 

 tance on the surface ; this is termed the aciculum. The 

 ordinary setae are exceedingly fine but stifnsh, 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 ap- 

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



noto\ 



neura 



rent.cirr 



FIG. 88. Nereis dumerilii. A single parapod ( x about 25). ac. aciculum ; dors, cirr, 

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

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



devoid of parapods, 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 parapcds, 

 there is in each segment a pair of very fine nephridio- 

 pores (p. 341), through which the sperms possibly pass 

 to the exterior, there being no special genital duct. 

 Dorsal pores are also wanting. 



The mouth leads into a wide buccal cavity, which is 

 continued back into a pharynx. In the pharynx are a 

 number of very small, dark brown, chitinous denticles, 

 which are very regularly arranged. The posterior part 



