XI 



POLYZOA 



391 



of the vibratile cleft, but after these have been given off the main 

 mass of the nerve fibres proceeds to the ciliated cells of the prototroch 

 or corona. Muscle fibres also go to the cells of the vibratile cleft, 



jf- 



cil 



CO 



FIG. 314. Median sagittal section of the fully grown Cyphonautes larva of Afembranipora 

 pilosa on the top of which have been traced certain structures (muscle fibres and corona, 

 etc.) lying to the right of the median plane. (After Kupelwieser, slightly altered.) 



Ad&, main adductor muscle of the valves ; Add?; accessory adductor muscle of the valves ; ap.g, 

 cells of the apical plate of the ganglionic nature ; ap.gl, cells of the apical plate of a glandular nature ; 

 ap.vis, cells of the apical plate of a visual nature ; cil, cells forming anterior and posterior borders of 

 the larva carrying long cilia ; co 1 , anterior section of the corona ; co 2 , posterior section of the corona ; 

 gr.c, granular cells; i.s, internal sac; int, intestine; m.e, mucous cells of mantle edge ; 7nnsc.circ.oes, 

 circular muscles surrounding the oesophagus ; m-usc.d, dorsal muscle ; musc.di, branch of dorsal muscle 

 which is inserted in the apical organ ; mwsc.d 2 , branch of dorsal muscle which curves back under the 

 apical organ and is inserted in the posterior section of the corona ; musc.lat.a, anterior part of lateral 

 muscle ; musc.lat.p, posterior part of lateral muscle ; musc.sk, sucker muscle ; ./, nerve fibres leading 

 from apical organ to vibratile plume and to corona ; oes, oesophagus ; p.o, piriform organ ; sec, 

 secretion produced by the cells of the internal sac ; v.cl, vibratile cleft ; v.pl, vibratile plume. 



and to the cells of the corona, but in addition muscle fibres are given 

 off which are inserted in the upper part of the piriform organ, and 

 others which encircle it after the manner of circular fibres. 



Kupelwieser regards the function of the piriform organ as skeletal, 



