PHYLUM ANNELIDA 



235 



nevertheless many differences. Both are segmented externally 

 and internally, but Nereis possesses parapodia (Fig. 164, para), 

 a pair of chitinous jaws, a pair of tentacles (tent), and two pairs 

 of eyes on the prostomium (praest), a pair of palpi (palp), 

 and four pairs of tentacles on the peristome (perisUent) . 



The parapodia (Fig. 165) 

 are primarily used as loco- 

 motor organs, but the lobes 

 (DP and VP) are supplied 

 with numerous blood- 

 vessels and serve also as 

 respiratory organs or gills. 

 Each parapodium bears 

 jointed locomotor setce, and 

 is moved by muscles at- 



bud 



DP 



Ac 



FIG. 165. Parapodium of 

 Nereis Ac, aciculum; Be, ven- 

 tral cirrus; DP, notopodium ; 

 Re, dorsal cirrus ; V P, neuro- 

 podium, with bundles of setae. 

 (From Sedgwick, after Quatre- 

 fages.) 



FIG. 166. APoly- 

 chaet, Autolytus, 

 which reproduces by 

 buds, bud, head of 

 the budded indi- 

 vidual. . (From 

 Davenport, after 

 Agassiz.) 



FIG. 167.^ Ant- 

 phitrite johnstoni. 

 g, gills ; /, prosto- 

 mial tentacles. 

 (From Sedgwick, 

 after Cunningham 

 and Ramage.) 



tached to a sort of internal skeleton consisting of two buried 

 bristles called acicula (Ac). 



The sense organs of Nereis are more highly developed than 

 those of the earthworm. The tentacles (Fig. 164, perist.tent) 

 are organs of touch, the palpi (palp) are probably organs of 

 taste, and the eyes, organs of sight. 



