CILIATA 



139 



This row passes to the left blunt angle, 



]>Ql: 



poc 



" adoral membranellae." 

 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 

 (?»). It forms the front 

 and left-hand boundary 

 of a wedge-shaped de- 

 pression, the " peri- 

 stomial area," the right- 

 hand boundary being 

 the " preoral ridge " or 

 lip {l), 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 " {poc) 

 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 Stylonychia), at the base and on 

 the inner side of each adoral membranella, is a " paroral ' cilium. 



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

 Abdominal cirrhi ; ayi, anus discharging the shell 

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

 CD, contractile vacuole ; e, part of its replenishing 

 canal ; f.c, frontal cirrhi ; f.v, food vacuoles ; r/, 

 internal undulating, membrane ; I, lip ; m, mouth 

 or pharynx ; one, marginal cirrhi ; N, i\^ . lobes of 

 meganucleus ; n, n, micronuclei ; 0, anterior end ; 

 per, adoral membranellae ; poc, preoral cilia ; p.om, 

 preoral undulating membrane ; s.h, sense hairs. 

 (Modified from Lang.) 



