ZooL.— Vol. III.] STEVENS— CILIA TE INFUSORIA. I>j 



when about 5 /^ in length, exhibited normal ciliary move- 

 ments, and corresponding sections showed a distinct basal 

 body for each cilium (fig. 15, x). Wallengren's pseu- 

 dopodia-like stage has not been observed and must be a 

 very early and brief condition, if it exists at all, for this 

 species. The ciliated area enlarges until its longitudinal 

 diameter is 30 /* to 40 yti, the extension being mainly towards 

 the attachment disc (figs. 19 and 20). The margin of 

 the area now becomes differentiated into a peristomal spiral 

 by the fusion of the basal bodies into transverse basal 

 bands, and the peristomal area assumes a ventral position. 

 The right hand end of the spire extends forward and to the 

 left. The cilia in the center of the area remain short (fig. 

 12, t), and are gradually reduced to papilla-like points 

 (fig. II, t), while those of the band rapidly lengthen. The 

 left hand end of the band, at first almost touching the 

 right (figs. II and 16), gradually moves outward by the 

 rapid growth of the area enclosed in the loop of the band, 

 passes over the posterior end of the body to the dorsal 

 side, and finally comes around to form a normal left hand 

 spiral (figs. 21 to 27). The lengthening of the band is 

 accompanied by separation of the transverse cilia-bearing 

 bands, and not by multiplication of those bands by division 

 (compare <5^ of fig. 11 with 3^ of fig. 4). The oral end of 

 the spiral band lies flat on the surface of the animal until 

 near the time of separation (fig. 27), when the mouth- 

 cavity appears and the band twists under the upper lip to 

 form the roof of the pharynx. At the time of separation, 

 and for some time after, the two individuals can be dis- 

 tinguished from each other by the position and size of the 

 mouth, and by the deeper staining qualities of the oral 

 band of the daughter animal. 



Wallengren speaks of a similar "Aufrollen" of the ciliary 

 band, but he describes the oral end as strongly inrolled. 

 " Aus der dexiotropen Spirale bildet sich durch Verschie- 

 bung die nach links gedrehte Peristomalzone des entwick- 

 elten Individuums dadurch aus, dass das am starksten 



(2) April 30, 1 90 1. 



