8 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



stout twist (figs. 4, ^ and 71). The transverse width of 

 these flat brushes, i. e., the width of the band, is least at 

 the beginning of the band (fig. 72) and is increased one- 

 half or more in the pharynx, the average width outside of 

 the mouth being 10/* in large living specimens. The cilia 

 of the several rows on the left side are most often seen 

 untwisted in the living animal at rest; while those on the 

 right side, where the band turns toward the mouth, are 

 often divided, one portion extending outward, the other 

 curving toward or into the mouth. The cilia are approxi- 

 mately equal in length throughout the band, 30 /* in living 

 and 18 /* in fixed material. Wallengren describes the oral 

 spire of L. auerbachii as consisting of stout membranell^ 

 set in a "Peristomalrinne," each membranella being broad 

 at the base and tapering out to a sharp point. These 

 tend to split up into fine fibrillas, long on the ventral side 

 and short on the dorsal. 



The most constant action of the oral cilia is a strong 

 stroke of the twisted rows toward the mouth, producing a 

 current in that direction, and rotating the body in the oppo- 

 site direction. In feeding, this movement alternates with 

 a second, in which the cilia of the posterior half of the 

 peristome are more or less untwisted and suddenly clapped 

 down on the ventral surface of the disc, driving food before 

 them toward the mouth. 



In sections fixed in Hermann's or Flemming's fluid and 

 stained with Heidenhain's iron-h^matoxylin, the oral band 

 is seen to have a complicated internal structure. At the 

 base of each row of cilia is a deeply stained basal band 

 whose ends are connected by fine fibres with an internal, 

 deeply staining fibre. A cross-section of the band presents 

 a triangular appearance with deeply stained basal band and 

 lateral fibres enclosing a dense homogeneous or finely granu- 

 lar portion. The proportions of the triangle vary greatly 

 from the beginning of the band to its end in the pharynx 



(%. 73)- 



Tracing these fibres back from the mouth-region around 



the peristome into the neck, their origin is found in a stout, 



longitudinally striated, deeply staining fibre, which arises 



