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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 97 



„ AlCnl DV 

 3 \ 



6 10 i VNC ^ 6 



Fig. 15. — The polychaete locomotor mechanism: parapodia, and somatic and 

 parapodial muscles of Nereis virens Sars. 



A, transverse section of a body segment, posterior view, somewhat diagram- 

 matic. B, a parapodium and its muscles, posterior view. C, chaetal apparatus 

 of a parapodium. D, muscles of right half of a body segment, inner view. 



Acic, acicula; AlCnl, alimentary canal; Ch, chaetae ; chS, chaetal sac; Cir, 

 cirrus ; dClt, dorsal chaetae ; dCir, dorsal cirrus ; Dsp, intersegmental dissepi- 

 ment ; DV, dorsal blood vessel; isf, intersegmental fold of integument; Papd, 

 parapodium ; vCh, ventral chaetae ; vCir, ventral cirrus ; VNC, ventral nerve 

 cord. 



I, circular muscles of body wall ; 2, oblique muscles of body wall ; 3, dorsal 

 longitudinal muscles ; 4, ventral longitudinal muscles ; 5, 6, anterior and pos- 

 terior lateroventral, obliquely transverse muscles ; 7, 8, dorsal motors of 

 parapodium ; g, 10, ventral motors of parapodium ; //, intrinsic muscle of para- 

 podium between dorsal and ventral lobes ; 12, protractors of dorsal acicula and 

 chaetal sac ; 13, 14, retractor and protractor of dorsal chaetae ; 15, retractor 

 of dorsal chaetal sac and acicula ; 16, protractors of ventral acicula and chaetal 

 sac ; 17, 18, retractor and protractor of ventral chaetae ; ig, retractor of ventral 

 chaetal sac. 



