REGENERATION I25 



of division, whereby the original feeding organelles are reduced in 

 size. The partial regression of the mouthparts at this time, in 

 which disappearance of the oral pouch as such is particularly 

 conspicuous, may represent the initial steps toward a remodeling 

 of the mouthparts on a smaller scale, but further changes are not 

 easily followed. 



We do not yet understand what determines the size or scale of 

 mouthparts formed anew. Experiments here are contradictory. 

 When a stage-3 regenerator was cut in two transversely through 

 the primordium and the anterior half rotated 180° on the posterior 

 the short anterior half anlage produced a tiny mouth while the 

 posterior section of equal length was completely employed in 

 forming a large one (Fig. 31 a). If the two fragments were entirely 

 separated, however, each portion of the primordium produced a 

 small and proportionate gullet and oral pouch in addition to the 

 membranellar band (b). An odd case, in which the regeneration 

 primordium was unusually short, produced a tiny set of mouth- 

 parts in a large stentor (c) ; but when a nucleated primordium sector 

 was isolated from a stage-4 regenerator the mouthparts were still 

 proportionate to the fragment although the anlage was of normal 

 length (d). When tail-poles were grafted into the frontal field and 

 reorganization followed, the mouthparts produced on the graft 

 were proportionate to its size, as were those on the host (e). Hence 

 in some cases the length of the primordium and in others the size 

 of the cell seemed to determine the scale of the parts produced. 



The most exaggerated requirement for an adjustment of cortical 

 organelles is occasioned by producing fragments which consist of 

 the head only (Tartar, i959d). By circumscribing the membran- 

 ellar band and cutting carefully around the oral pouch and gullet 

 so as not to disturb them, fragments were cut which contained 

 only the feeding organelles intact, the frontal field, a little endo- 

 plasm, and usually one or two of the most anterior macronuclear 

 nodes. Much shorter than the anterior fragments cut by Morgan, 

 these pieces folded on themselves in healing to produce spheres in 

 which the membranellar band was thrown into coils like the 

 stitching on a baseball (Figs. 32 and 86c). In these specimens there 

 was no primordium formation, but the membranellar band soon 

 decreased in length as it became normally disposed and the 

 mouthparts were later gradually reduced in size, while ecto- 



