no 



THE BIOLOGY OF STENTOR 



(b) Regeneration of the holdfast 



This occurs much more readily and quickly than oral regenera- 

 tion. It can even take place in the absence of the nucleus (Tartar, 

 1956c). Within 2 hours after excision a new attachment organelle 

 is formed (Morgan, 1901a; Weisz, 1951b). By removing holdfasts 

 and posterior portions of the left boundary stripe of the ramifying 

 zone, Weisz showed that a new tail was then produced at the 

 posterior terminus of the stripes remaining, even if this led to a 

 holdfast appearing forward and projecting laterally (Fig. 26a). 

 (Actually a substantial portion of the ramifying zone must have 

 been removed.) The regenerated holdfast then moved toward the 

 posterior pole, possibly through an accelerated growth of the 

 striping anterior to it. When the original holdfast was not removed 

 the new one was soon resorbed. I have found that when a stentor 

 is cut in two transversely and the anterior half rotated 180° on the 

 posterior so that the lateral striping is out of alignment and does 

 not rejoin, a new tail is sometimes formed and projects temporarily 

 from the oral meridian of the anterior part (b). Likewise, if the 

 ramifying zone is circumscribed and rotated in place its posterior 

 end regenerates a new holdfast projecting forward (c). Consonant 

 with these results, Weisz offered two important principles of 

 holdfast regeneration: first, the presence of one good organelle 



Fig. 27. Unusual tail-pole and holdfast formation in folded 

 non-oral halves, a: Longitudinal cut through the axis to yield 

 aboral half lacking widest and narrowest pigment stripes, b: 

 Wound healed by folding which brings head and tail-poles 

 together, polarities indicated, c: Lateral striping is self-severed 

 across the sharp bend of the fold, giving same appearance as a 

 fission line. Oral primordium develops where widest granular 

 stripes lie adjacent to their attenuated extensions, d: Cut ends 

 of striping drawn together to form a new pole. Original half-tail 

 extends temporarily but is later resorbed as the new holdfast 

 becomes functional {e). (After Tartar, 1956b.) 



