CILIATES 197 



both migrants and sessile adults. In the migrant the cilia of the 

 trochal band arise from kinetosomes aligned in short oblique 

 rows within the band encircling the cell. The kinetosomes, of 

 conventional structure, are directly linked to one another along 

 each row by fibrous bridges (Fig. 81, PI. XXII). At the same level 

 a continuous heavy fiber or band of filaments parallels the row 

 along one side and is attached to each kinetosome. At a deeper 

 level a fibril arises from each kinetosome and passes in a direction 

 perpendicular to the oblique row. The length and course of 

 these fibrils are unknown, but the authors suggest that they may 

 represent kinetodesma and in the original print supplied by 

 Prof. Faure-Fremiet traces of cross-banding are detectable. In 

 addition to the fibrous structures, rows of tiny vesicles and tubules 

 are aligned close to the oblique fiber paralleling each row. Adult 

 cells have no aboral cilia and a reduced number of kinetosomes in 

 the aboral band, and these lack associated fibers entirely. They 

 seem to be open apically, ending at or slightly removed from the 

 inner surface of the pellicle. Granules appear in the core of the 

 kinetosomes in this stage. 



Subclass Spirotrichia 



Order Heterotrichida 



Among the six orders of the Subclass . Spirotrichia, the 

 Heterotrichida occupy a central position comparable to that 

 accorded the gymnostomes and hymenostomes among the 

 Holotrichia. Most heterotrichs have a holotrich-like uniform 

 somatic ciliature, but all display the spiraled adoral zone of 

 membranelles that is the major distinguishing feature of the 

 subclass. The buccal cavity typically is a broadly expanded funnel, 

 the peristome. In recent years the esthetically delightful 

 heterotrich, Stentor, has achieved a status almost rivaling those of 

 Paramecium and Amoeba as an experimental organism (see Tartar, 

 1961). This is largely because of its extraordinary amenity to 

 surgical methods that in the hands particularly of Tartar and of 

 Weisz (1954, 1956) have yielded invaluable information on 

 morphogenesis, but also because of its phenomenal contractility 

 and extensibility. Since Stentor has a precise and intricate cortical 

 architecture whose main features are readily observed even at 



