554 Annals of the South African Museum. 



back or front view, and the space between the cilia is very clear 

 (cf. Plate XXXIX, A). 



At the point of insertion of each cilium is a highly refractive 

 granule, the " Basal Granule " of Zimmermann (1921, p. 285). These 

 are beautifully seen if the microscope is focussed well above the 

 surface of a colony held in place by a supported cover-slip, and 

 then gradually lowered. As the objective is focussed down the 

 lashing upper portions of the cilia first appear and the circular move- 

 ment can be watched, then the two bright basal granules, the space 

 between them sometimes nearly half the diameter of the protoplast, 

 then the eyespots (if cells in the anterior half are in question), and, 

 finally, the broad base of the cell with its central pyrenoid and con- 

 necting strands. 



The base of the cilium just above the basal granule is slightly 

 thickened ; as the cilium passes through the outer membrane it 

 thins down, the projecting part being apparently of almost uniform 

 thickness, tapering very slightly at the end. The projecting por- 

 tions of the cilia are differentiated into a more rigid lower third 

 and a flexible outer part, which lashes vigorously, describing a curve 

 in a plane more or less concentric with the surface of the colony 

 and separated from it by the length of the rigid lower portion. The 

 rapid movement of the cilia in the natural state makes the study of 

 their action difficult, but if the coenobium is held in place by the cover- 

 slip, after a time the action begins to slow down and the actual move- 

 ment of the flexible part can be watched. The action is most easily 

 explained by comparison with a whip which has a short, rigid handle 

 and a long lash, which, after lashing forward, is drawn back with a 

 circular movement. In fixed material the cilia often show a spiral 

 twist at the base of the flexible part. 



No rhizoplast connecting the cilia to the nucleus could be seen 

 either in living material or in freshly killed preparations, but signs 

 of such a structure have been traced in some of the microtomed 

 sections, though without sufficient definition to arrive at any con- 

 clusion as to its structure or nature. Zimmermann (1921, p. 218) 

 failed to see rhizoplasts in the vegetative cells of V. globator, but 

 considered that they were probably present, just as in the repro- 

 ductive cells. 



The cilia become very evident if the colony is killed by running in 

 a drop of iodine solution, and even more so if dilute osmic acid is used 

 as the killing agent. In section the cilia stain well with gentian violet. 



(v) Eyespot or Stigma. The eyespot or stigma is a very con- 



