2/0 



POLYCHAETA 



Amongst the Nereidiformia the jaws are absent in the Phyllo- 

 docidae and Hesionidae ; when present they are usually set in 

 the direct course of the food. There may be one small tooth used 

 for stabbing, as in some Syllids (Fig. 141, A) ; or a circle of such 

 denticles (Autolytus, Fig. 140, D). To these are added powerful 

 grasping jaws in Nereis (E) ; or the latter may alone be pre- 

 sent, as in Glycera (F). In Polynoe the four jaws are carried 



FIG. 140. Jaws of various Chaetopods. A, Transverse section of the anterior end of 

 Eunice ; a, b, c, d, various parts of the upper series of denticles lying in a special 

 chamber ; g, oesophagus ; k, lower jaw : B, the denticles of Eunice separated ; U, 

 upper series ; a, grinder ; 6, forceps ; c, rasping plates ; d, grater ; L, lower series ; j, 

 tooth ; k, base into which muscles are inserted : C, Polynoid ; U, upper, and L, 

 lower jaws ; j, tooth ; k, base : D, Diagrammatic section across pharynx of Auto- 

 lytus; E, ot Nereis; F, of Glycera; Q, of Polynoe. 



by hard pieces, to which the muscles are attached (C and G). In 

 Nephthys there is a dorsal and a ventral jaw. 



In the Eunicidae, however, the numerous denticles are carried 

 in a special pouch below the food tract, with which it communi- 

 cates anteriorly. 1 They are arranged in an upper and lower 

 series. The lower series (L) consists of a pair of flat plates (&) 

 on each side partially embedded in and acted upon by muscles, 

 with a harder enamelled piece the actual lower " tooth " (f) 

 at its anterior end. The upper series (U) consists of several 



pieces, varying in shape and size in the various genera of this 







1 Compare with this the muscular organ of Dinoj>hilus, p. 243, Protodrilus, and 

 a similar structure which occurs in Terebellids-:. 



