igo MANUAL OF ZOOLOGY SECT. 



tentacles (tent.}, and further back a pair of somewhat longer 

 stout appendages or palpi (palp.). The peristomium, which 

 bears some resemblance to the segments of the body, though 

 wanting the parapodia, bears laterally four pairs of long slender 

 cylindrical tentacles (perist. tent.) : on its ventral aspect is a 

 transversely elongated aperture, the aperture of the mouth. 

 The segments of the body differ little in external characters 

 from one another throughout the length of the worm. Each 

 bears laterally a pair of parapodia, which in the living 

 animal are usually in active movement, aiding in creeping, 



dors, cirr 



noto 



neuro 



~"^^^ 

 vent. cirr 



FIG. loi. Nereis dumerilii. A single parapodium magnified, ac. aciculum ; 

 dors. cirr. dorsal cirrus ; neuro. neuropodium ; noto. notopodium ; vent. cirr. 

 ventral cirrus. (After Claparede.) 



or acting as a series of oars for propelling it through the 

 water. When one of the parapodia (Fig. 101) is examined 

 more attentively it is found to be biramous, or to consist of 

 two distinct divisions a dorsal, which is termed the 

 notopodium (noto.\ and a ventral, which is termed the neuro- 

 podium (neuro?). Each of these is further subdivided into 

 several lobes, and each bears a bundle of setae. Each of 

 the bundles of setae is lodged in a sac formed by invagina- 

 tion of the epidermis, the setigerous sac, and is capable of 

 being protruded or retracted and turned in various directions 

 by bundles of muscular fibres in the interior of the 



