POLYCHAETA 265 



filiform, tactile appendages, the tentacles which are dorsal and the 

 palps which are ventral ; there are also one or two pairs of eyes upon 

 it. The anterior part of the gat (pharynx) is eversible and serves for 

 grasping food ; its lining may be chitinized in places to form the jaws 

 and paragnaths oi Nereis or teeth as in Syllis. These are not necessarily 



^^^^•^•->^ . pr. ten. 



ac^ 



r^ieur. 



Fig. 184. Nereis. A, Dorsal view of head and ifirst trunk segments with 

 everted pharynx. B, Side view of same with pharynx retracted. C, Para- 

 podium of unmodified type. D, Parapodium of Heteronereis. E, Example of 

 unmodified compound chaeta. F, Oar-shaped compound chaeta of Hetero- 

 nereis. The peristomium is stippled, pr. prostomium; ten. tentacle;^, palp; 

 ten.c. peristomial cirri ; d.c. dorsal cirrus ; v.c. ventral cirrus ; not. notopodium ; 

 neur. neuropodium ; /./. foliaceous outgrowths of parapodia ; ac. aciculum ; 

 ch. chaetae ; ch. oar-shaped chaetae ; j. jaws ; pg. paragnaths. 



the sign of a carnivorous habit but may be used for cutting up pieces 

 of seaweed or boring in sponges. , 



The ordinary trunk segment has a double parapodium consisting 

 of a dorsal notopodium and a ventral neuropodium ^ usually with rather 

 different types of chaetae. A dorsal cirrus and a ventral cirrus are 

 nearly always present ; they are filiform structures but may be modi- 

 fied to form pectinate gills [Eunice) or plate-like elytra (Polynoidae). 



