CILIATA 



139 



This 



" adoral menil)ranellae." 

 and there crosses over 

 the edge of the body to 

 the ventral aspect, and 

 then curves inwards 

 towards the median line, 

 which it reaches about 

 half-way back, where it 

 passes into the pharynx 

 (7/1). It forms the front 

 and left-hand boundary 

 of a wedge-shaped de- 

 pression, the " peri- 

 stomial area," the right- 

 hand lioundary being 

 the " preoral ridge " or 

 lip (/), which runs 

 nearly on the median 

 line, projecting down- 

 ward and over the de- 

 pression. This ridge 

 bears on its inner and 

 upper side a row of fine 

 " preoral cilia " (p<>c) 

 and a wide " preoral 

 undulating membrane " 

 (p.om), which extends 

 horizontally across, be- 

 low the peristomial area. 

 The roof of this area 

 bears along its right- 

 hand edge an " internal 

 undulating membrane " 

 (g), and then, as we 

 pass across to the left, 

 first an " endoral mem- 

 brane " and then an 

 " endoral " row of cilia. 



In some allied genera (not in Stj/Ionj/chia), at 

 the inner side of each adoral memljranella, is a 



row passes to the left blunt angle. 





PiQ. 49.— Ventral view of Stylonychia mytilus. a.c, 

 Alxloniiiial cirrlii ; an, anus discharging the shell 

 of a Diatom ; c.c, camlal cirrhi ; c.p, dorsal cirrhi ; 

 cr, contractile vacuole ; e, part of its replenishing 

 canal ;/.c, frontal cirrhi ; /.r, food vacuoles; n, 

 internal undulating niennbrane ; I, lip ; ?", mouth 

 or pharynx ; mc, marginal cirrhi ; iV, N, lobes of 

 nieganucleus ; n, n, micronuclei ; 0, anterior end ; 

 2^er, adoral memliranellae : por, preoral cilia ; j^.om, 

 preoral undulating membrane ; .?.//, sense hairs. 

 (Modified from Lang.) 



the base and on 

 ' paroral ' cilium. 



