No. 478] ODONTOPHORAL APPARATUS IN SYCOTYPUS 713 



entail a sliding of the membrane — a thing which anatomical 

 examination has shown us as being impossible (Fig. 45, PI. V) 

 [the figure is for Helix pomatia, but his assertion is a general one, 

 see p. 147, and refers to Prosobranchs too], and wliich direct obser- 

 vation has never established [?]. Further, a traction produced 

 upon one pomt only of the membrane would occasion ni n not 

 only a slidmg motion but also the production ot tolds in it. and 

 then, w^hether the flexd)le radula should follow the contours ot tlie 

 folded siu'face or wliether it should pass beyond, in either case it 

 would be 111 an unfit state for plaving its role of rasp." 



It IS clear therefore that Amaudrut regards as ten^wr.s- what other 

 ob.servers and I have considered as protractors and retractors ot 

 the radula. ho far as Sycotypus is concerned he is m error, tor 

 by direct observation one can easily convince oneself ot the slidin^; 

 motion of the radula m this large uastroixxl. 



His explanation is as follows: 1 he ini[)onant ditlerenco m 

 the general mechanism which exist between the Piihnoiiafa and 

 the Rachiqhsm. are that, with th<- latter wh.-n the flexors [pro- 

 tia.tois] ot tlu . ntiliiits (ont.<i<t tlu Mniiinii ..t th. t.)iiji . 

 not onK .h lun Un^^ u.l but tlu 1 itn ,1 t..th m^u .1. ui.l ulun 



ilu t.Mwar.l p..M.i..n tlu n.th ot tlu tip .>t tlu t.>nuit i,. .i> th. 

 mouthtul tio.n buuat . tlun it .1. lun m, cut ort In pressure 



